Patchwork PCI: add a quirk for keeping Bus Master bit on shutdown

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Submitter Chang Liu
Date Nov. 12, 2013, 7:40 p.m.
Message ID <1384285203-642-1-git-send-email-cl91tp@gmail.com>
Download mbox | patch
Permalink /patch/290591/
State Rejected
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Chang Liu - Nov. 12, 2013, 7:40 p.m.
This fixes https://bugzilla.kernel.org/show_bug.cgi?id=63861

Commit b566a22c2 and 7897e60227 made pci_device_shutdown()
unconditionally clear Bus Master bit for every pci devices.
While this works for most hardware, certain devices are not
compatible with this. Intel Lynx Point-LP SATA Controller,
for example, will hang the system if its Bus Master bit is
cleared during device shutdown. This patch adds a pci quirk
so that device drivers can instruct pci_device_shutdown()
to keep Bus Master from being cleared, and then implements
this mechanism for the Intel Lynx Point-LP AHCI driver.

Signed-off-by: Chang Liu <cl91tp@gmail.com>
---
As per Takao's suggestion, add a new member into struct pci_dev
and add a quirk in the ahci driver. I tested this on my
machine (Acer V5-573G) and it works fine.

 drivers/ata/ahci.c       |  8 ++++++++
 drivers/pci/pci-driver.c | 11 ++++++++---
 include/linux/pci.h      |  1 +
 3 files changed, 17 insertions(+), 3 deletions(-)
Bjorn Helgaas - Nov. 26, 2013, 3:33 a.m.
[+cc Lan, Khalid, Konstantin, Alan, Takao, Jility, Florian, linux-kernel]

On Tue, Nov 12, 2013 at 07:40:03PM +0000, Chang Liu wrote:
> This fixes https://bugzilla.kernel.org/show_bug.cgi?id=63861
>
> Commit b566a22c2 and 7897e60227 made pci_device_shutdown()
> unconditionally clear Bus Master bit for every pci devices.
> While this works for most hardware, certain devices are not
> compatible with this. Intel Lynx Point-LP SATA Controller,
> for example, will hang the system if its Bus Master bit is
> cleared during device shutdown. This patch adds a pci quirk
> so that device drivers can instruct pci_device_shutdown()
> to keep Bus Master from being cleared, and then implements
> this mechanism for the Intel Lynx Point-LP AHCI driver.
>
> Signed-off-by: Chang Liu <cl91tp@gmail.com>

I'm not 100% comfortable with disabling bus mastering in general;
see [1] for more details.

But given that we have been doing it for quite a while (b566a22c2 appeared
in v3.5 on Jul 21, 2012), and Lynx Point should be in lots of machines, I'm
surprised that we don't see more reports of this problem if it really
affects all Lynx Point parts.

Jility reported the same problem [2], and I did find one other similar
report [3] from Florian.  All three reports (Chang, Jility, Florian) are on
the same exact machine (Acer V5-573G), which seems sort of suspicious.

Lan, do you have access to any Lynx Point boxes?  Can you test and see
whether they hang on power-off also?  I suspect this might be something
specific to the Acer box, not a generic Lynx Point issue.

Bjorn

[1] http://lkml.kernel.org/r/20120427190033.GA17588@ldl.usa.hp.com
[2] https://bugzilla.kernel.org/show_bug.cgi?id=63861#c21
[3] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1249329

> ---
> As per Takao's suggestion, add a new member into struct pci_dev
> and add a quirk in the ahci driver. I tested this on my
> machine (Acer V5-573G) and it works fine.
>
>  drivers/ata/ahci.c       |  8 ++++++++
>  drivers/pci/pci-driver.c | 11 ++++++++---
>  include/linux/pci.h      |  1 +
>  3 files changed, 17 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
> index 8e28f92..de6efcb 100644
> --- a/drivers/ata/ahci.c
> +++ b/drivers/ata/ahci.c
> @@ -1385,6 +1385,14 @@ static int ahci_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
>
>   pci_set_master(pdev);
>
> + /* We normally clear Bus Master on pci device shutdown. However,
> + * doing so for Intel Lynx Point-LP SATA Controller [AHCI mode]
> + * hangs the system. Therefore keep it.
> + * See bug report: https://bugzilla.kernel.org/show_bug.cgi?id=63861
> + */
> + if (pdev->vendor == PCI_VENDOR_ID_INTEL && pdev->device == 0x9c03)
> + pdev->keep_busmaster_on_shutdown = 1;
> +
>   if (hpriv->flags & AHCI_HFLAG_MULTI_MSI)
>   return ahci_host_activate(host, pdev->irq, n_msis);
>
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index 38f3c01..ff15b0c 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -392,10 +392,15 @@ static void pci_device_shutdown(struct device *dev)
>   pci_msix_shutdown(pci_dev);
>
>   /*
> - * Turn off Bus Master bit on the device to tell it to not
> - * continue to do DMA. Don't touch devices in D3cold or unknown states.
> + * If the hardware is okay with it, turn off Bus Master bit
> + * on the device to tell it not to continue doing DMA.
> + * Don't touch devices in D3cold or unknown states.
> + * On certain hardware clearing Bus Master bit on shutdown
> + * may hang the entire system. In these cases the driver of
> + * these devices should set keep_busmaster_on_shutdown to 1.
>   */
> - if (pci_dev->current_state <= PCI_D3hot)
> + if (!pci_dev->keep_busmaster_on_shutdown
> +    && pci_dev->current_state <= PCI_D3hot)
>   pci_clear_master(pci_dev);
>  }
>
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index da172f9..63db735 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -322,6 +322,7 @@ struct pci_dev {
>   /* keep track of device state */
>   unsigned int is_added:1;
>   unsigned int is_busmaster:1; /* device is busmaster */
> + unsigned int keep_busmaster_on_shutdown:1; /* do not clear busmaster on shutdown */
>   unsigned int no_msi:1; /* device may not use msi */
>   unsigned int block_cfg_access:1; /* config space access is blocked */
>   unsigned int broken_parity_status:1; /* Device generates false positive parity */
> --
> 1.8.4.2
>
> --
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Chang Liu - Nov. 26, 2013, 4:11 a.m.
If this turns out to be a problem specific to Acer V573G, we can simply
wrap the if (pdev->...) line in ata/ahci.c with if
(dmi_check_system(acer_v573g))
so that only acer v573g laptops will be affected by this patch. The remaining
part of the patch won't need to be changed.

I can do an updated one as soon as it is confirmed that this is an acer specific
issue.

2013/11/26 Bjorn Helgaas <bhelgaas@google.com>:
> [+cc Lan, Khalid, Konstantin, Alan, Takao, Jility, Florian, linux-kernel]
>
> On Tue, Nov 12, 2013 at 07:40:03PM +0000, Chang Liu wrote:
>> This fixes https://bugzilla.kernel.org/show_bug.cgi?id=63861
>>
>> Commit b566a22c2 and 7897e60227 made pci_device_shutdown()
>> unconditionally clear Bus Master bit for every pci devices.
>> While this works for most hardware, certain devices are not
>> compatible with this. Intel Lynx Point-LP SATA Controller,
>> for example, will hang the system if its Bus Master bit is
>> cleared during device shutdown. This patch adds a pci quirk
>> so that device drivers can instruct pci_device_shutdown()
>> to keep Bus Master from being cleared, and then implements
>> this mechanism for the Intel Lynx Point-LP AHCI driver.
>>
>> Signed-off-by: Chang Liu <cl91tp@gmail.com>
>
> I'm not 100% comfortable with disabling bus mastering in general;
> see [1] for more details.
>
> But given that we have been doing it for quite a while (b566a22c2 appeared
> in v3.5 on Jul 21, 2012), and Lynx Point should be in lots of machines, I'm
> surprised that we don't see more reports of this problem if it really
> affects all Lynx Point parts.
>
> Jility reported the same problem [2], and I did find one other similar
> report [3] from Florian.  All three reports (Chang, Jility, Florian) are on
> the same exact machine (Acer V5-573G), which seems sort of suspicious.
>
> Lan, do you have access to any Lynx Point boxes?  Can you test and see
> whether they hang on power-off also?  I suspect this might be something
> specific to the Acer box, not a generic Lynx Point issue.
>
> Bjorn
>
> [1] http://lkml.kernel.org/r/20120427190033.GA17588@ldl.usa.hp.com
> [2] https://bugzilla.kernel.org/show_bug.cgi?id=63861#c21
> [3] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1249329
>
>> ---
>> As per Takao's suggestion, add a new member into struct pci_dev
>> and add a quirk in the ahci driver. I tested this on my
>> machine (Acer V5-573G) and it works fine.
>>
>>  drivers/ata/ahci.c       |  8 ++++++++
>>  drivers/pci/pci-driver.c | 11 ++++++++---
>>  include/linux/pci.h      |  1 +
>>  3 files changed, 17 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
>> index 8e28f92..de6efcb 100644
>> --- a/drivers/ata/ahci.c
>> +++ b/drivers/ata/ahci.c
>> @@ -1385,6 +1385,14 @@ static int ahci_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
>>
>>   pci_set_master(pdev);
>>
>> + /* We normally clear Bus Master on pci device shutdown. However,
>> + * doing so for Intel Lynx Point-LP SATA Controller [AHCI mode]
>> + * hangs the system. Therefore keep it.
>> + * See bug report: https://bugzilla.kernel.org/show_bug.cgi?id=63861
>> + */
>> + if (pdev->vendor == PCI_VENDOR_ID_INTEL && pdev->device == 0x9c03)
>> + pdev->keep_busmaster_on_shutdown = 1;
>> +
>>   if (hpriv->flags & AHCI_HFLAG_MULTI_MSI)
>>   return ahci_host_activate(host, pdev->irq, n_msis);
>>
>> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
>> index 38f3c01..ff15b0c 100644
>> --- a/drivers/pci/pci-driver.c
>> +++ b/drivers/pci/pci-driver.c
>> @@ -392,10 +392,15 @@ static void pci_device_shutdown(struct device *dev)
>>   pci_msix_shutdown(pci_dev);
>>
>>   /*
>> - * Turn off Bus Master bit on the device to tell it to not
>> - * continue to do DMA. Don't touch devices in D3cold or unknown states.
>> + * If the hardware is okay with it, turn off Bus Master bit
>> + * on the device to tell it not to continue doing DMA.
>> + * Don't touch devices in D3cold or unknown states.
>> + * On certain hardware clearing Bus Master bit on shutdown
>> + * may hang the entire system. In these cases the driver of
>> + * these devices should set keep_busmaster_on_shutdown to 1.
>>   */
>> - if (pci_dev->current_state <= PCI_D3hot)
>> + if (!pci_dev->keep_busmaster_on_shutdown
>> +    && pci_dev->current_state <= PCI_D3hot)
>>   pci_clear_master(pci_dev);
>>  }
>>
>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>> index da172f9..63db735 100644
>> --- a/include/linux/pci.h
>> +++ b/include/linux/pci.h
>> @@ -322,6 +322,7 @@ struct pci_dev {
>>   /* keep track of device state */
>>   unsigned int is_added:1;
>>   unsigned int is_busmaster:1; /* device is busmaster */
>> + unsigned int keep_busmaster_on_shutdown:1; /* do not clear busmaster on shutdown */
>>   unsigned int no_msi:1; /* device may not use msi */
>>   unsigned int block_cfg_access:1; /* config space access is blocked */
>>   unsigned int broken_parity_status:1; /* Device generates false positive parity */
>> --
>> 1.8.4.2
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-pci" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
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Bjorn Helgaas - Nov. 26, 2013, 4:20 a.m.
On Mon, Nov 25, 2013 at 9:11 PM, Chang Liu <cl91tp@gmail.com> wrote:
> If this turns out to be a problem specific to Acer V573G, we can simply
> wrap the if (pdev->...) line in ata/ahci.c with if
> (dmi_check_system(acer_v573g))
> so that only acer v573g laptops will be affected by this patch. The remaining
> part of the patch won't need to be changed.

Well, sure.  But that doesn't change the fact that until we know *why*
it hangs, this is voodoo programming.  And I don't like voodoo
programming.

> 2013/11/26 Bjorn Helgaas <bhelgaas@google.com>:
>> [+cc Lan, Khalid, Konstantin, Alan, Takao, Jility, Florian, linux-kernel]
>>
>> On Tue, Nov 12, 2013 at 07:40:03PM +0000, Chang Liu wrote:
>>> This fixes https://bugzilla.kernel.org/show_bug.cgi?id=63861
>>>
>>> Commit b566a22c2 and 7897e60227 made pci_device_shutdown()
>>> unconditionally clear Bus Master bit for every pci devices.
>>> While this works for most hardware, certain devices are not
>>> compatible with this. Intel Lynx Point-LP SATA Controller,
>>> for example, will hang the system if its Bus Master bit is
>>> cleared during device shutdown. This patch adds a pci quirk
>>> so that device drivers can instruct pci_device_shutdown()
>>> to keep Bus Master from being cleared, and then implements
>>> this mechanism for the Intel Lynx Point-LP AHCI driver.
>>>
>>> Signed-off-by: Chang Liu <cl91tp@gmail.com>
>>
>> I'm not 100% comfortable with disabling bus mastering in general;
>> see [1] for more details.
>>
>> But given that we have been doing it for quite a while (b566a22c2 appeared
>> in v3.5 on Jul 21, 2012), and Lynx Point should be in lots of machines, I'm
>> surprised that we don't see more reports of this problem if it really
>> affects all Lynx Point parts.
>>
>> Jility reported the same problem [2], and I did find one other similar
>> report [3] from Florian.  All three reports (Chang, Jility, Florian) are on
>> the same exact machine (Acer V5-573G), which seems sort of suspicious.
>>
>> Lan, do you have access to any Lynx Point boxes?  Can you test and see
>> whether they hang on power-off also?  I suspect this might be something
>> specific to the Acer box, not a generic Lynx Point issue.
>>
>> Bjorn
>>
>> [1] http://lkml.kernel.org/r/20120427190033.GA17588@ldl.usa.hp.com
>> [2] https://bugzilla.kernel.org/show_bug.cgi?id=63861#c21
>> [3] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1249329
>>
>>> ---
>>> As per Takao's suggestion, add a new member into struct pci_dev
>>> and add a quirk in the ahci driver. I tested this on my
>>> machine (Acer V5-573G) and it works fine.
>>>
>>>  drivers/ata/ahci.c       |  8 ++++++++
>>>  drivers/pci/pci-driver.c | 11 ++++++++---
>>>  include/linux/pci.h      |  1 +
>>>  3 files changed, 17 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
>>> index 8e28f92..de6efcb 100644
>>> --- a/drivers/ata/ahci.c
>>> +++ b/drivers/ata/ahci.c
>>> @@ -1385,6 +1385,14 @@ static int ahci_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
>>>
>>>   pci_set_master(pdev);
>>>
>>> + /* We normally clear Bus Master on pci device shutdown. However,
>>> + * doing so for Intel Lynx Point-LP SATA Controller [AHCI mode]
>>> + * hangs the system. Therefore keep it.
>>> + * See bug report: https://bugzilla.kernel.org/show_bug.cgi?id=63861
>>> + */
>>> + if (pdev->vendor == PCI_VENDOR_ID_INTEL && pdev->device == 0x9c03)
>>> + pdev->keep_busmaster_on_shutdown = 1;
>>> +
>>>   if (hpriv->flags & AHCI_HFLAG_MULTI_MSI)
>>>   return ahci_host_activate(host, pdev->irq, n_msis);
>>>
>>> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
>>> index 38f3c01..ff15b0c 100644
>>> --- a/drivers/pci/pci-driver.c
>>> +++ b/drivers/pci/pci-driver.c
>>> @@ -392,10 +392,15 @@ static void pci_device_shutdown(struct device *dev)
>>>   pci_msix_shutdown(pci_dev);
>>>
>>>   /*
>>> - * Turn off Bus Master bit on the device to tell it to not
>>> - * continue to do DMA. Don't touch devices in D3cold or unknown states.
>>> + * If the hardware is okay with it, turn off Bus Master bit
>>> + * on the device to tell it not to continue doing DMA.
>>> + * Don't touch devices in D3cold or unknown states.
>>> + * On certain hardware clearing Bus Master bit on shutdown
>>> + * may hang the entire system. In these cases the driver of
>>> + * these devices should set keep_busmaster_on_shutdown to 1.
>>>   */
>>> - if (pci_dev->current_state <= PCI_D3hot)
>>> + if (!pci_dev->keep_busmaster_on_shutdown
>>> +    && pci_dev->current_state <= PCI_D3hot)
>>>   pci_clear_master(pci_dev);
>>>  }
>>>
>>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>>> index da172f9..63db735 100644
>>> --- a/include/linux/pci.h
>>> +++ b/include/linux/pci.h
>>> @@ -322,6 +322,7 @@ struct pci_dev {
>>>   /* keep track of device state */
>>>   unsigned int is_added:1;
>>>   unsigned int is_busmaster:1; /* device is busmaster */
>>> + unsigned int keep_busmaster_on_shutdown:1; /* do not clear busmaster on shutdown */
>>>   unsigned int no_msi:1; /* device may not use msi */
>>>   unsigned int block_cfg_access:1; /* config space access is blocked */
>>>   unsigned int broken_parity_status:1; /* Device generates false positive parity */
>>> --
>>> 1.8.4.2
>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-pci" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
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Lan Tianyu - Nov. 26, 2013, 5:39 a.m.
On 2013年11月26日 11:33, Bjorn Helgaas wrote:
> Lan, do you have access to any Lynx Point boxes?  Can you test and see
> whether they hang on power-off also?  I suspect this might be something
> specific to the Acer box, not a generic Lynx Point issue.

Sure. I just get one such prototype laptop and power off works normally
on it.
Khalid Aziz - Nov. 26, 2013, 4:40 p.m.
On 11/25/2013 08:33 PM, Bjorn Helgaas wrote:
> [+cc Lan, Khalid, Konstantin, Alan, Takao, Jility, Florian, linux-kernel]
>
> On Tue, Nov 12, 2013 at 07:40:03PM +0000, Chang Liu wrote:
>> This fixes https://bugzilla.kernel.org/show_bug.cgi?id=63861
>>
>> Commit b566a22c2 and 7897e60227 made pci_device_shutdown()
>> unconditionally clear Bus Master bit for every pci devices.
>> While this works for most hardware, certain devices are not
>> compatible with this. Intel Lynx Point-LP SATA Controller,
>> for example, will hang the system if its Bus Master bit is
>> cleared during device shutdown. This patch adds a pci quirk
>> so that device drivers can instruct pci_device_shutdown()
>> to keep Bus Master from being cleared, and then implements
>> this mechanism for the Intel Lynx Point-LP AHCI driver.
>>
>> Signed-off-by: Chang Liu <cl91tp@gmail.com>
>
> I'm not 100% comfortable with disabling bus mastering in general;
> see [1] for more details.

Disabling Bus Master bit is effectively a brute force and not an elegant 
way to stop unwanted DMA. It can have side effects as Alan and others 
pointed out in the original discussion, and we are now seeing one with 
Lynx Point on Acer. Eric had pointed out in original discussion - 
<http://marc.info/?l=linux-pci&m=133901193430829&w=2> that this code 
change moves failure from a random point in the kexec'd kernel to a 
predictable point on shutdown path where it becomes lot easier to debug 
than a random memory overwrite. For kexec and kdump to be successful, 
all devices need to be shut down cleanly and be in a state where they 
can be reinitialized by the kexec'd kernel. Either device drivers do it 
or we forcibly stop all DMAs by clearing Bus Master bit. If we stop 
clearing Bus Master bit on shutdown, we will resurrect the old issue of 
random memory corruption on kexec.

Regular shutdown being affected by Bus Master bit being cleared is not a 
comfortable situation. Would it be better if we clear Bus Master bit 
only if devices are being shut down in preparation for kexec?

Patch proposed by Chang Liu is similar to the approach I had suggested 
in discussions last year - 
<http://marc.info/?l=linux-pci&m=133900414027717&w=2> where driver tells 
the PCI subsystem if it is not ok with Bus Master bit being cleared and 
I can accept this approach. Every time we come across a broken 
driver/device that implodes on Bus Master bit being cleared, we add 
"pdev->keep_busmaster_on_shutdown = 1;" to the driver. This will be an 
ongoing process.

--
Khalid

>
> But given that we have been doing it for quite a while (b566a22c2 appeared
> in v3.5 on Jul 21, 2012), and Lynx Point should be in lots of machines, I'm
> surprised that we don't see more reports of this problem if it really
> affects all Lynx Point parts.
>
> Jility reported the same problem [2], and I did find one other similar
> report [3] from Florian.  All three reports (Chang, Jility, Florian) are on
> the same exact machine (Acer V5-573G), which seems sort of suspicious.
>
> Lan, do you have access to any Lynx Point boxes?  Can you test and see
> whether they hang on power-off also?  I suspect this might be something
> specific to the Acer box, not a generic Lynx Point issue.
>
> Bjorn
>
> [1] http://lkml.kernel.org/r/20120427190033.GA17588@ldl.usa.hp.com
> [2] https://bugzilla.kernel.org/show_bug.cgi?id=63861#c21
> [3] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1249329
>
>> ---
>> As per Takao's suggestion, add a new member into struct pci_dev
>> and add a quirk in the ahci driver. I tested this on my
>> machine (Acer V5-573G) and it works fine.
>>
>>   drivers/ata/ahci.c       |  8 ++++++++
>>   drivers/pci/pci-driver.c | 11 ++++++++---
>>   include/linux/pci.h      |  1 +
>>   3 files changed, 17 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
>> index 8e28f92..de6efcb 100644
>> --- a/drivers/ata/ahci.c
>> +++ b/drivers/ata/ahci.c
>> @@ -1385,6 +1385,14 @@ static int ahci_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
>>
>>    pci_set_master(pdev);
>>
>> + /* We normally clear Bus Master on pci device shutdown. However,
>> + * doing so for Intel Lynx Point-LP SATA Controller [AHCI mode]
>> + * hangs the system. Therefore keep it.
>> + * See bug report: https://bugzilla.kernel.org/show_bug.cgi?id=63861
>> + */
>> + if (pdev->vendor == PCI_VENDOR_ID_INTEL && pdev->device == 0x9c03)
>> + pdev->keep_busmaster_on_shutdown = 1;
>> +
>>    if (hpriv->flags & AHCI_HFLAG_MULTI_MSI)
>>    return ahci_host_activate(host, pdev->irq, n_msis);
>>
>> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
>> index 38f3c01..ff15b0c 100644
>> --- a/drivers/pci/pci-driver.c
>> +++ b/drivers/pci/pci-driver.c
>> @@ -392,10 +392,15 @@ static void pci_device_shutdown(struct device *dev)
>>    pci_msix_shutdown(pci_dev);
>>
>>    /*
>> - * Turn off Bus Master bit on the device to tell it to not
>> - * continue to do DMA. Don't touch devices in D3cold or unknown states.
>> + * If the hardware is okay with it, turn off Bus Master bit
>> + * on the device to tell it not to continue doing DMA.
>> + * Don't touch devices in D3cold or unknown states.
>> + * On certain hardware clearing Bus Master bit on shutdown
>> + * may hang the entire system. In these cases the driver of
>> + * these devices should set keep_busmaster_on_shutdown to 1.
>>    */
>> - if (pci_dev->current_state <= PCI_D3hot)
>> + if (!pci_dev->keep_busmaster_on_shutdown
>> +    && pci_dev->current_state <= PCI_D3hot)
>>    pci_clear_master(pci_dev);
>>   }
>>
>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>> index da172f9..63db735 100644
>> --- a/include/linux/pci.h
>> +++ b/include/linux/pci.h
>> @@ -322,6 +322,7 @@ struct pci_dev {
>>    /* keep track of device state */
>>    unsigned int is_added:1;
>>    unsigned int is_busmaster:1; /* device is busmaster */
>> + unsigned int keep_busmaster_on_shutdown:1; /* do not clear busmaster on shutdown */
>>    unsigned int no_msi:1; /* device may not use msi */
>>    unsigned int block_cfg_access:1; /* config space access is blocked */
>>    unsigned int broken_parity_status:1; /* Device generates false positive parity */
>> --
>> 1.8.4.2
>>
>> --
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>> the body of a message to majordomo@vger.kernel.org
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Bjorn Helgaas - Nov. 26, 2013, 5:35 p.m.
[+cc Eric, Matthew]

On Tue, Nov 26, 2013 at 9:40 AM, Khalid Aziz <khalid.aziz@oracle.com> wrote:
> On 11/25/2013 08:33 PM, Bjorn Helgaas wrote:
>>
>> [+cc Lan, Khalid, Konstantin, Alan, Takao, Jility, Florian, linux-kernel]
>>
>> On Tue, Nov 12, 2013 at 07:40:03PM +0000, Chang Liu wrote:
>>>
>>> This fixes https://bugzilla.kernel.org/show_bug.cgi?id=63861
>>>
>>> Commit b566a22c2 and 7897e60227 made pci_device_shutdown()
>>> unconditionally clear Bus Master bit for every pci devices.
>>> While this works for most hardware, certain devices are not
>>> compatible with this. Intel Lynx Point-LP SATA Controller,
>>> for example, will hang the system if its Bus Master bit is
>>> cleared during device shutdown. This patch adds a pci quirk
>>> so that device drivers can instruct pci_device_shutdown()
>>> to keep Bus Master from being cleared, and then implements
>>> this mechanism for the Intel Lynx Point-LP AHCI driver.
>>>
>>> Signed-off-by: Chang Liu <cl91tp@gmail.com>
>>
>> I'm not 100% comfortable with disabling bus mastering in general;
>> see [1] for more details.
>
> Disabling Bus Master bit is effectively a brute force and not an elegant way
> to stop unwanted DMA. It can have side effects as Alan and others pointed
> out in the original discussion, and we are now seeing one with Lynx Point on
> Acer.

I'm getting more queasy all the time about disabling Bus Master.  I
don't think RHEL does it, and that's probably where most kexec use is.
 So I doubt we really have much experience with it yet.

> Eric had pointed out in original discussion -
> <http://marc.info/?l=linux-pci&m=133901193430829&w=2> that this code change
> moves failure from a random point in the kexec'd kernel to a predictable
> point on shutdown path where it becomes lot easier to debug than a random
> memory overwrite.

That is probably true in some cases, but not this one.  I have no idea
how to debug this poweroff hang.  Poweroff is a path *everybody* uses,
so it's much more important to have that work reliably than it is to
have kexec work.

> For kexec and kdump to be successful, all devices need to
> be shut down cleanly and be in a state where they can be reinitialized by
> the kexec'd kernel. Either device drivers do it or we forcibly stop all DMAs
> by clearing Bus Master bit. If we stop clearing Bus Master bit on shutdown,
> we will resurrect the old issue of random memory corruption on kexec.

Well, there *are* more degrees of freedom here.  If we don't reuse the
memory of the old kernel, any ongoing DMA will only affect the old
kernel image, not the new one.  So I don't think disabling Bus Master
is the only possible strategy.

> Regular shutdown being affected by Bus Master bit being cleared is not a
> comfortable situation. Would it be better if we clear Bus Master bit only if
> devices are being shut down in preparation for kexec?
>
> Patch proposed by Chang Liu is similar to the approach I had suggested in
> discussions last year -
> <http://marc.info/?l=linux-pci&m=133900414027717&w=2> where driver tells the
> PCI subsystem if it is not ok with Bus Master bit being cleared and I can
> accept this approach. Every time we come across a broken driver/device that
> implodes on Bus Master bit being cleared, we add
> "pdev->keep_busmaster_on_shutdown = 1;" to the driver. This will be an
> ongoing process.

I am really uncomfortable with this ongoing process because the people
who will trip over these imploding devices are non-technical users who
bought a new machine or are just trying out Linux.  They do something
completely normal like turn off their machine, and it blows up.  Their
only real options are to return the machine or ditch Linux.

Kexec is a 1% case and we're probably using it because we've already
crashed for another reason, and we're already in the unreliable state,
so if kexec breaks it's not such a user-experience nightmare.

I wonder if there's any other way we could make progress on the
original kexec corruption issues.  Maybe there's some logging we could
add to make active drivers more visible.

>> But given that we have been doing it for quite a while (b566a22c2 appeared
>> in v3.5 on Jul 21, 2012), and Lynx Point should be in lots of machines,
>> I'm
>> surprised that we don't see more reports of this problem if it really
>> affects all Lynx Point parts.
>>
>> Jility reported the same problem [2], and I did find one other similar
>> report [3] from Florian.  All three reports (Chang, Jility, Florian) are
>> on
>> the same exact machine (Acer V5-573G), which seems sort of suspicious.
>>
>> Lan, do you have access to any Lynx Point boxes?  Can you test and see
>> whether they hang on power-off also?  I suspect this might be something
>> specific to the Acer box, not a generic Lynx Point issue.
>>
>> Bjorn
>>
>> [1] http://lkml.kernel.org/r/20120427190033.GA17588@ldl.usa.hp.com
>> [2] https://bugzilla.kernel.org/show_bug.cgi?id=63861#c21
>> [3] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1249329
>>
>>> ---
>>> As per Takao's suggestion, add a new member into struct pci_dev
>>> and add a quirk in the ahci driver. I tested this on my
>>> machine (Acer V5-573G) and it works fine.
>>>
>>>   drivers/ata/ahci.c       |  8 ++++++++
>>>   drivers/pci/pci-driver.c | 11 ++++++++---
>>>   include/linux/pci.h      |  1 +
>>>   3 files changed, 17 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
>>> index 8e28f92..de6efcb 100644
>>> --- a/drivers/ata/ahci.c
>>> +++ b/drivers/ata/ahci.c
>>> @@ -1385,6 +1385,14 @@ static int ahci_init_one(struct pci_dev *pdev,
>>> const struct pci_device_id *ent)
>>>
>>>    pci_set_master(pdev);
>>>
>>> + /* We normally clear Bus Master on pci device shutdown. However,
>>> + * doing so for Intel Lynx Point-LP SATA Controller [AHCI mode]
>>> + * hangs the system. Therefore keep it.
>>> + * See bug report: https://bugzilla.kernel.org/show_bug.cgi?id=63861
>>> + */
>>> + if (pdev->vendor == PCI_VENDOR_ID_INTEL && pdev->device == 0x9c03)
>>> + pdev->keep_busmaster_on_shutdown = 1;
>>> +
>>>    if (hpriv->flags & AHCI_HFLAG_MULTI_MSI)
>>>    return ahci_host_activate(host, pdev->irq, n_msis);
>>>
>>> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
>>> index 38f3c01..ff15b0c 100644
>>> --- a/drivers/pci/pci-driver.c
>>> +++ b/drivers/pci/pci-driver.c
>>> @@ -392,10 +392,15 @@ static void pci_device_shutdown(struct device *dev)
>>>    pci_msix_shutdown(pci_dev);
>>>
>>>    /*
>>> - * Turn off Bus Master bit on the device to tell it to not
>>> - * continue to do DMA. Don't touch devices in D3cold or unknown states.
>>> + * If the hardware is okay with it, turn off Bus Master bit
>>> + * on the device to tell it not to continue doing DMA.
>>> + * Don't touch devices in D3cold or unknown states.
>>> + * On certain hardware clearing Bus Master bit on shutdown
>>> + * may hang the entire system. In these cases the driver of
>>> + * these devices should set keep_busmaster_on_shutdown to 1.
>>>    */
>>> - if (pci_dev->current_state <= PCI_D3hot)
>>> + if (!pci_dev->keep_busmaster_on_shutdown
>>> +    && pci_dev->current_state <= PCI_D3hot)
>>>    pci_clear_master(pci_dev);
>>>   }
>>>
>>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>>> index da172f9..63db735 100644
>>> --- a/include/linux/pci.h
>>> +++ b/include/linux/pci.h
>>> @@ -322,6 +322,7 @@ struct pci_dev {
>>>    /* keep track of device state */
>>>    unsigned int is_added:1;
>>>    unsigned int is_busmaster:1; /* device is busmaster */
>>> + unsigned int keep_busmaster_on_shutdown:1; /* do not clear busmaster on
>>> shutdown */
>>>    unsigned int no_msi:1; /* device may not use msi */
>>>    unsigned int block_cfg_access:1; /* config space access is blocked */
>>>    unsigned int broken_parity_status:1; /* Device generates false
>>> positive parity */
>>> --
>>> 1.8.4.2
>>>
>>> --
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>>> the body of a message to majordomo@vger.kernel.org
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>
>
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Matthew Garrett - Nov. 26, 2013, 5:48 p.m.
On Tue, Nov 26, 2013 at 10:35:26AM -0700, Bjorn Helgaas wrote:
> On Tue, Nov 26, 2013 at 9:40 AM, Khalid Aziz <khalid.aziz@oracle.com> wrote:
> > Disabling Bus Master bit is effectively a brute force and not an elegant way
> > to stop unwanted DMA. It can have side effects as Alan and others pointed
> > out in the original discussion, and we are now seeing one with Lynx Point on
> > Acer.
> 
> I'm getting more queasy all the time about disabling Bus Master.  I
> don't think RHEL does it, and that's probably where most kexec use is.
>  So I doubt we really have much experience with it yet.

Does Windows disable the BM bit on shutdown? If not, it's likely that 
there are platforms where the SMM code assumes it's still enabled. We 
also know that there are devices that hang if BM is disabled while their 
DMA engines are still running.

Unless we verify that Windows does this, I think there's no way we can 
guarantee that firmware won't make assumptions about the state of PCI. 
The easiest compromise would probably be to set a flag that disables 
busmastering purely when we're performing a kexec.

> > Eric had pointed out in original discussion -
> > <http://marc.info/?l=linux-pci&m=133901193430829&w=2> that this code change
> > moves failure from a random point in the kexec'd kernel to a predictable
> > point on shutdown path where it becomes lot easier to debug than a random
> > memory overwrite.
> 
> That is probably true in some cases, but not this one.  I have no idea
> how to debug this poweroff hang.  Poweroff is a path *everybody* uses,
> so it's much more important to have that work reliably than it is to
> have kexec work.

If it's hanging after we've performed the io writes that trap us into 
SMM, there's no meaningful way for us to debug it. We're violating 
assumptions that the firmware is making, and the only way to fix that is 
to cease violating those assumptions.

Patch

diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
index 8e28f92..de6efcb 100644
--- a/drivers/ata/ahci.c
+++ b/drivers/ata/ahci.c
@@ -1385,6 +1385,14 @@  static int ahci_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 
 	pci_set_master(pdev);
 
+	/* We normally clear Bus Master on pci device shutdown. However,
+	 * doing so for Intel Lynx Point-LP SATA Controller [AHCI mode]
+	 * hangs the system. Therefore keep it.
+	 * See bug report: https://bugzilla.kernel.org/show_bug.cgi?id=63861
+	 */
+	if (pdev->vendor == PCI_VENDOR_ID_INTEL && pdev->device == 0x9c03)
+		pdev->keep_busmaster_on_shutdown = 1;
+
 	if (hpriv->flags & AHCI_HFLAG_MULTI_MSI)
 		return ahci_host_activate(host, pdev->irq, n_msis);
 
diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index 38f3c01..ff15b0c 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -392,10 +392,15 @@  static void pci_device_shutdown(struct device *dev)
 	pci_msix_shutdown(pci_dev);
 
 	/*
-	 * Turn off Bus Master bit on the device to tell it to not
-	 * continue to do DMA. Don't touch devices in D3cold or unknown states.
+	 * If the hardware is okay with it, turn off Bus Master bit
+	 * on the device to tell it not to continue doing DMA.
+	 * Don't touch devices in D3cold or unknown states.
+	 * On certain hardware clearing Bus Master bit on shutdown
+	 * may hang the entire system. In these cases the driver of
+	 * these devices should set keep_busmaster_on_shutdown to 1.
 	 */
-	if (pci_dev->current_state <= PCI_D3hot)
+	if (!pci_dev->keep_busmaster_on_shutdown
+	    && pci_dev->current_state <= PCI_D3hot)
 		pci_clear_master(pci_dev);
 }
 
diff --git a/include/linux/pci.h b/include/linux/pci.h
index da172f9..63db735 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -322,6 +322,7 @@  struct pci_dev {
 	/* keep track of device state */
 	unsigned int	is_added:1;
 	unsigned int	is_busmaster:1; /* device is busmaster */
+	unsigned int	keep_busmaster_on_shutdown:1; /* do not clear busmaster on shutdown */
 	unsigned int	no_msi:1;	/* device may not use msi */
 	unsigned int	block_cfg_access:1;	/* config space access is blocked */
 	unsigned int	broken_parity_status:1;	/* Device generates false positive parity */