diff mbox

[V2] powerpc/kernel/sysfs: disable writing to purr in non-powernv

Message ID 1380281634-9921-1-git-send-email-maddy@linux.vnet.ibm.com (mailing list archive)
State Superseded
Headers show

Commit Message

maddy Sept. 27, 2013, 11:33 a.m. UTC 
powerpc/kernel/sysfs.c exports purr with write permission.
This is only valid for kernel in hypervisor mode.
But writing to the file in PowerVM lpar causes crash.

# echo 0 > purr
cpu 0x0: Vector: 700 (Program Check) at [c000000000d072b0]
    pc: c00000000001770c: .write_purr+0x1c/0x40
    lr: c000000000017708: .write_purr+0x18/0x40
    sp: c000000000d07530
   msr: 8000000000049032
  current = 0xc000000000c53de0
  paca    = 0xc00000000ec70000	 softe: 0	 irq_happened: 0x01
    pid   = 0, comm = swapper/0
enter ? for help
[c000000000d075b0] c0000000000fba64
.generic_smp_call_function_single_interrupt+0x104/0x190
[c000000000d07650] c000000000037748 .smp_ipi_demux+0xa8/0xf0
[c000000000d076e0] c000000000035314 .doorbell_exception+0x74/0xb0
[c000000000d07760] c000000000002950 doorbell_super_common+0x150/0x180
--- Exception: a01 (Doorbell) at c000000000060904
.plpar_hcall_norets+0x84/0xd4
[link register   ] c00000000006dbd4 .check_and_cede_processor+0x24/0x40
[c000000000d07a50] c000000001002558 (unreliable)
[c000000000d07ac0] c00000000006dd0c .shared_cede_loop+0x2c/0x70
[c000000000d07b40] c0000000006ae954 .cpuidle_enter_state+0x64/0x150
[c000000000d07c00] c0000000006aeb30 .cpuidle_idle_call+0xf0/0x300
[c000000000d07cb0] c000000000062fa0 .pseries_lpar_idle+0x10/0x50
[c000000000d07d20] c000000000016d14 .arch_cpu_idle+0x64/0x150
[c000000000d07da0] c0000000000e0060 .cpu_startup_entry+0x1a0/0x2c0
[c000000000d07e80] c00000000000bca4 .rest_init+0x94/0xb0
[c000000000d07ef0] c000000000b54530 .start_kernel+0x478/0x494
[c000000000d07f90] c000000000009be0 .start_here_common+0x20/0x40
0:mon>

Changes:

1)Changed the test for to hypervisor mode instead of platform

Signed-off-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/sysfs.c |   20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

Comments

Michael Ellerman Oct. 1, 2013, 6:31 a.m. UTC | #1 
Hi Maddy,

On Fri, Sep 27, 2013 at 05:03:54PM +0530, Madhavan Srinivasan wrote:
> powerpc/kernel/sysfs.c exports purr with write permission.

PURR

> This is only valid for kernel in hypervisor mode.
> But writing to the file in PowerVM lpar causes crash.

In the kernel history/source we refer to it as "phyp". However in this
case it's not an issue with phyp, it's simply that you are not in
hypervisor mode, ie. the same crash would occur under KVM.

So you should just say "writing to the file in guest mode .."

> # echo 0 > purr
> cpu 0x0: Vector: 700 (Program Check) at [c000000000d072b0]
>     pc: c00000000001770c: .write_purr+0x1c/0x40
>     lr: c000000000017708: .write_purr+0x18/0x40
>     sp: c000000000d07530
>    msr: 8000000000049032
>   current = 0xc000000000c53de0
>   paca    = 0xc00000000ec70000	 softe: 0	 irq_happened: 0x01
>     pid   = 0, comm = swapper/0
> enter ? for help
> [c000000000d075b0] c0000000000fba64
> .generic_smp_call_function_single_interrupt+0x104/0x190
> [c000000000d07650] c000000000037748 .smp_ipi_demux+0xa8/0xf0
> [c000000000d076e0] c000000000035314 .doorbell_exception+0x74/0xb0
> [c000000000d07760] c000000000002950 doorbell_super_common+0x150/0x180
> --- Exception: a01 (Doorbell) at c000000000060904
> .plpar_hcall_norets+0x84/0xd4
> [link register   ] c00000000006dbd4 .check_and_cede_processor+0x24/0x40
> [c000000000d07a50] c000000001002558 (unreliable)
> [c000000000d07ac0] c00000000006dd0c .shared_cede_loop+0x2c/0x70
> [c000000000d07b40] c0000000006ae954 .cpuidle_enter_state+0x64/0x150
> [c000000000d07c00] c0000000006aeb30 .cpuidle_idle_call+0xf0/0x300
> [c000000000d07cb0] c000000000062fa0 .pseries_lpar_idle+0x10/0x50
> [c000000000d07d20] c000000000016d14 .arch_cpu_idle+0x64/0x150
> [c000000000d07da0] c0000000000e0060 .cpu_startup_entry+0x1a0/0x2c0
> [c000000000d07e80] c00000000000bca4 .rest_init+0x94/0xb0
> [c000000000d07ef0] c000000000b54530 .start_kernel+0x478/0x494
> [c000000000d07f90] c000000000009be0 .start_here_common+0x20/0x40
> 0:mon>
> 
> Changes:
> 
> 1)Changed the test for to hypervisor mode instead of platform

I think Ben's wrong about that.

Almost all existing code uses FW_FEATURE_LPAR to differentiate
hypervisor vs guest mode, so I think we should do the same here.

So it would be:

> +	if (cpu_has_feature(CPU_FTR_PURR)) {
> +		if (!firmware_has_feature(FW_FEATURE_LPAR))
> +			add_write_permission_dev_attr((void *)&dev_attr_purr);
>  		device_create_file(s, &dev_attr_purr);
> +	}


> +static void add_write_permission_dev_attr(void *ptr)
> +{
> +	struct device_attribute *attr = (struct device_attribute *)ptr;
> +
> +	attr->attr.mode |= (unsigned short) 0200;
> +}

Why does it take a void *, which then requires a cast at the call site?

And do you need the cast to short? If so shouldn't you use umode_t
directly?

cheers
Benjamin Herrenschmidt Oct. 1, 2013, 7:50 a.m. UTC | #2 
On Tue, 2013-10-01 at 16:31 +1000, Michael Ellerman wrote:

> > 1)Changed the test for to hypervisor mode instead of platform
> 
> I think Ben's wrong about that.
> 
> Almost all existing code uses FW_FEATURE_LPAR to differentiate
> hypervisor vs guest mode, so I think we should do the same here.

I didn't object to using the FW test, it's a reasonable way to do it, I
objected to using the platform as an indication (powernv vs. pseries)

Ben.

> So it would be:
> 
> > +	if (cpu_has_feature(CPU_FTR_PURR)) {
> > +		if (!firmware_has_feature(FW_FEATURE_LPAR))
> > +			add_write_permission_dev_attr((void *)&dev_attr_purr);
> >  		device_create_file(s, &dev_attr_purr);
> > +	}
> 
> 
> > +static void add_write_permission_dev_attr(void *ptr)
> > +{
> > +	struct device_attribute *attr = (struct device_attribute *)ptr;
> > +
> > +	attr->attr.mode |= (unsigned short) 0200;
> > +}
> 
> Why does it take a void *, which then requires a cast at the call site?
> 
> And do you need the cast to short? If so shouldn't you use umode_t
> directly?
> 
> cheers
maddy Oct. 1, 2013, 8:09 a.m. UTC | #3 
On Tuesday 01 October 2013 12:01 PM, Michael Ellerman wrote:
> Hi Maddy,
> 
> On Fri, Sep 27, 2013 at 05:03:54PM +0530, Madhavan Srinivasan wrote:
>> powerpc/kernel/sysfs.c exports purr with write permission.
> 
> PURR
> 
>> This is only valid for kernel in hypervisor mode.
>> But writing to the file in PowerVM lpar causes crash.
> 
> In the kernel history/source we refer to it as "phyp". However in this

Will follow the convention.

> case it's not an issue with phyp, it's simply that you are not in
> hypervisor mode, ie. the same crash would occur under KVM.
> 
> So you should just say "writing to the file in guest mode .."
> 

Sure. Will make the changes.

>> # echo 0 > purr
>> cpu 0x0: Vector: 700 (Program Check) at [c000000000d072b0]
>>     pc: c00000000001770c: .write_purr+0x1c/0x40
>>     lr: c000000000017708: .write_purr+0x18/0x40
>>     sp: c000000000d07530
>>    msr: 8000000000049032
>>   current = 0xc000000000c53de0
>>   paca    = 0xc00000000ec70000	 softe: 0	 irq_happened: 0x01
>>     pid   = 0, comm = swapper/0
>> enter ? for help
>> [c000000000d075b0] c0000000000fba64
>> .generic_smp_call_function_single_interrupt+0x104/0x190
>> [c000000000d07650] c000000000037748 .smp_ipi_demux+0xa8/0xf0
>> [c000000000d076e0] c000000000035314 .doorbell_exception+0x74/0xb0
>> [c000000000d07760] c000000000002950 doorbell_super_common+0x150/0x180
>> --- Exception: a01 (Doorbell) at c000000000060904
>> .plpar_hcall_norets+0x84/0xd4
>> [link register   ] c00000000006dbd4 .check_and_cede_processor+0x24/0x40
>> [c000000000d07a50] c000000001002558 (unreliable)
>> [c000000000d07ac0] c00000000006dd0c .shared_cede_loop+0x2c/0x70
>> [c000000000d07b40] c0000000006ae954 .cpuidle_enter_state+0x64/0x150
>> [c000000000d07c00] c0000000006aeb30 .cpuidle_idle_call+0xf0/0x300
>> [c000000000d07cb0] c000000000062fa0 .pseries_lpar_idle+0x10/0x50
>> [c000000000d07d20] c000000000016d14 .arch_cpu_idle+0x64/0x150
>> [c000000000d07da0] c0000000000e0060 .cpu_startup_entry+0x1a0/0x2c0
>> [c000000000d07e80] c00000000000bca4 .rest_init+0x94/0xb0
>> [c000000000d07ef0] c000000000b54530 .start_kernel+0x478/0x494
>> [c000000000d07f90] c000000000009be0 .start_here_common+0x20/0x40
>> 0:mon>
>>
>> Changes:
>>
>> 1)Changed the test for to hypervisor mode instead of platform
> 
> I think Ben's wrong about that.
> 
> Almost all existing code uses FW_FEATURE_LPAR to differentiate
> hypervisor vs guest mode, so I think we should do the same here.
> 
> So it would be:
> 
>> +	if (cpu_has_feature(CPU_FTR_PURR)) {
>> +		if (!firmware_has_feature(FW_FEATURE_LPAR))
>> +			add_write_permission_dev_attr((void *)&dev_attr_purr);
>>  		device_create_file(s, &dev_attr_purr);
>> +	}
>

Will modify the check.

> 
>> +static void add_write_permission_dev_attr(void *ptr)
>> +{
>> +	struct device_attribute *attr = (struct device_attribute *)ptr;
>> +
>> +	attr->attr.mode |= (unsigned short) 0200;
>> +}
> 
> Why does it take a void *, which then requires a cast at the call site?
>

just prefered to send the address as void.

> And do you need the cast to short? If so shouldn't you use umode_t
> directly?

No, not really.
Will make the changes and will resend the patch.

> 
> cheers
> 
Thanks for feedback.
Maddy
Michael Ellerman Oct. 1, 2013, 8:43 a.m. UTC | #4 
On Tue, Oct 01, 2013 at 05:50:30PM +1000, Benjamin Herrenschmidt wrote:
> On Tue, 2013-10-01 at 16:31 +1000, Michael Ellerman wrote:
> 
> > > 1)Changed the test for to hypervisor mode instead of platform
> > 
> > I think Ben's wrong about that.
> > 
> > Almost all existing code uses FW_FEATURE_LPAR to differentiate
> > hypervisor vs guest mode, so I think we should do the same here.
> 
> I didn't object to using the FW test, it's a reasonable way to do it, I
> objected to using the platform as an indication (powernv vs. pseries)

Yeah sorry I wasn't clear. You are right that it shouldn't use the
platform. So I think we agree FW_FEATURE is the right way to go.

cheers
diff mbox

Patch

diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c
index 27a90b9..42becfa 100644
--- a/arch/powerpc/kernel/sysfs.c
+++ b/arch/powerpc/kernel/sysfs.c
@@ -17,6 +17,7 @@ 
 #include <asm/machdep.h>
 #include <asm/smp.h>
 #include <asm/pmc.h>
+#include <asm/reg.h>
 
 #include "cacheinfo.h"
 
@@ -179,15 +180,27 @@  SYSFS_PMCSETUP(spurr, SPRN_SPURR);
 SYSFS_PMCSETUP(dscr, SPRN_DSCR);
 SYSFS_PMCSETUP(pir, SPRN_PIR);
 
+/*
+  Lets only enable Read for Hyp resources and
+  enable Write when needed with a separate function.
+  Lets be conservative and default to pseries.
+*/
 static DEVICE_ATTR(mmcra, 0600, show_mmcra, store_mmcra);
 static DEVICE_ATTR(spurr, 0400, show_spurr, NULL);
 static DEVICE_ATTR(dscr, 0600, show_dscr, store_dscr);
-static DEVICE_ATTR(purr, 0600, show_purr, store_purr);
+static DEVICE_ATTR(purr, 0400, show_purr, store_purr);
 static DEVICE_ATTR(pir, 0400, show_pir, NULL);
 
 unsigned long dscr_default = 0;
 EXPORT_SYMBOL(dscr_default);
 
+static void add_write_permission_dev_attr(void *ptr)
+{
+	struct device_attribute *attr = (struct device_attribute *)ptr;
+
+	attr->attr.mode |= (unsigned short) 0200;
+}
+
 static ssize_t show_dscr_default(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {
@@ -394,8 +407,11 @@  static void register_cpu_online(unsigned int cpu)
 	if (cpu_has_feature(CPU_FTR_MMCRA))
 		device_create_file(s, &dev_attr_mmcra);
 
-	if (cpu_has_feature(CPU_FTR_PURR))
+	if (cpu_has_feature(CPU_FTR_PURR)) {
+		if (mfmsr() & MSR_HV)
+			add_write_permission_dev_attr((void *)&dev_attr_purr);
 		device_create_file(s, &dev_attr_purr);
+	}
 
 	if (cpu_has_feature(CPU_FTR_SPURR))
 		device_create_file(s, &dev_attr_spurr);