| Message ID | 20240215074823.51014-1-mhklinux@outlook.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v2,1/1] PCI: hv: Fix ring buffer size calculation | expand |
On Wed, 14 Feb 2024, mhkelley58@gmail.com wrote: > From: Michael Kelley <mhklinux@outlook.com> > > For a physical PCI device that is passed through to a Hyper-V guest VM, > current code specifies the VMBus ring buffer size as 4 pages. But this > is an inappropriate dependency, since the amount of ring buffer space > needed is unrelated to PAGE_SIZE. For example, on x86 the ring buffer > size ends up as 16 Kbytes, while on ARM64 with 64 Kbyte pages, the ring > size bloats to 256 Kbytes. The ring buffer for PCI pass-thru devices > is used for only a few messages during device setup and removal, so any > space above a few Kbytes is wasted. > > Fix this by declaring the ring buffer size to be a fixed 16 Kbytes. > Furthermore, use the VMBUS_RING_SIZE() macro so that the ring buffer > header is properly accounted for, and so the size is rounded up to a > page boundary, using the page size for which the kernel is built. While > w/64 Kbyte pages this results in a 64 Kbyte ring buffer header plus a > 64 Kbyte ring buffer, that's the smallest possible with that page size. > It's still 128 Kbytes better than the current code. > > Cc: <stable@vger.kernel.org> # 5.15.x > Signed-off-by: Michael Kelley <mhklinux@outlook.com> > Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com> > --- > Changes in v2: > * Use SZ_16K instead of 16 * 1024 > --- > drivers/pci/controller/pci-hyperv.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c > index 1eaffff40b8d..baadc1e5090e 100644 > --- a/drivers/pci/controller/pci-hyperv.c > +++ b/drivers/pci/controller/pci-hyperv.c > @@ -465,7 +465,7 @@ struct pci_eject_response { > u32 status; > } __packed; > > -static int pci_ring_size = (4 * PAGE_SIZE); > +static int pci_ring_size = VMBUS_RING_SIZE(SZ_16K); > > /* > * Driver specific state. > Hi, You forgot to add #include <linux/sizes.h> for it. With that fixed: Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
From: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com> Sent: Friday, February 16, 2024 6:46 AM > > On Wed, 14 Feb 2024, mhkelley58@gmail.com wrote: > > > > For a physical PCI device that is passed through to a Hyper-V guest VM, > > current code specifies the VMBus ring buffer size as 4 pages. But this > > is an inappropriate dependency, since the amount of ring buffer space > > needed is unrelated to PAGE_SIZE. For example, on x86 the ring buffer > > size ends up as 16 Kbytes, while on ARM64 with 64 Kbyte pages, the ring > > size bloats to 256 Kbytes. The ring buffer for PCI pass-thru devices > > is used for only a few messages during device setup and removal, so any > > space above a few Kbytes is wasted. > > > > Fix this by declaring the ring buffer size to be a fixed 16 Kbytes. > > Furthermore, use the VMBUS_RING_SIZE() macro so that the ring buffer > > header is properly accounted for, and so the size is rounded up to a > > page boundary, using the page size for which the kernel is built. While > > w/64 Kbyte pages this results in a 64 Kbyte ring buffer header plus a > > 64 Kbyte ring buffer, that's the smallest possible with that page size. > > It's still 128 Kbytes better than the current code. > > > > Cc: <stable@vger.kernel.org> # 5.15.x > > Signed-off-by: Michael Kelley <mhklinux@outlook.com> > > Reviewed-by: Kuppuswamy Sathyanarayanan > <sathyanarayanan.kuppuswamy@linux.intel.com> > > --- > > Changes in v2: > > * Use SZ_16K instead of 16 * 1024 > > --- > > drivers/pci/controller/pci-hyperv.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci- > hyperv.c > > index 1eaffff40b8d..baadc1e5090e 100644 > > --- a/drivers/pci/controller/pci-hyperv.c > > +++ b/drivers/pci/controller/pci-hyperv.c > > @@ -465,7 +465,7 @@ struct pci_eject_response { > > u32 status; > > } __packed; > > > > -static int pci_ring_size = (4 * PAGE_SIZE); > > +static int pci_ring_size = VMBUS_RING_SIZE(SZ_16K); > > > > /* > > * Driver specific state. > > > > Hi, > > You forgot to add #include <linux/sizes.h> for it. > > With that fixed: > > Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com> > Fixed in v3. I mis-interpreted your previous comment about adding the #include "if needed". It's not needed to compile correctly, as sizes.h is indirectly included through some other #include. But it's better to directly #include what's needed lest some unrelated change cause a failure. Michael
On Fri, 16 Feb 2024, Michael Kelley wrote: > From: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com> Sent: Friday, February 16, 2024 6:46 AM > > > > On Wed, 14 Feb 2024, mhkelley58@gmail.com wrote: > > > > > > For a physical PCI device that is passed through to a Hyper-V guest VM, > > > current code specifies the VMBus ring buffer size as 4 pages. But this > > > is an inappropriate dependency, since the amount of ring buffer space > > > needed is unrelated to PAGE_SIZE. For example, on x86 the ring buffer > > > size ends up as 16 Kbytes, while on ARM64 with 64 Kbyte pages, the ring > > > size bloats to 256 Kbytes. The ring buffer for PCI pass-thru devices > > > is used for only a few messages during device setup and removal, so any > > > space above a few Kbytes is wasted. > > > > > > Fix this by declaring the ring buffer size to be a fixed 16 Kbytes. > > > Furthermore, use the VMBUS_RING_SIZE() macro so that the ring buffer > > > header is properly accounted for, and so the size is rounded up to a > > > page boundary, using the page size for which the kernel is built. While > > > w/64 Kbyte pages this results in a 64 Kbyte ring buffer header plus a > > > 64 Kbyte ring buffer, that's the smallest possible with that page size. > > > It's still 128 Kbytes better than the current code. > > > > > > Cc: <stable@vger.kernel.org> # 5.15.x > > > Signed-off-by: Michael Kelley <mhklinux@outlook.com> > > > Reviewed-by: Kuppuswamy Sathyanarayanan > > <sathyanarayanan.kuppuswamy@linux.intel.com> > > > --- > > > Changes in v2: > > > * Use SZ_16K instead of 16 * 1024 > > > --- > > > drivers/pci/controller/pci-hyperv.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci- > > hyperv.c > > > index 1eaffff40b8d..baadc1e5090e 100644 > > > --- a/drivers/pci/controller/pci-hyperv.c > > > +++ b/drivers/pci/controller/pci-hyperv.c > > > @@ -465,7 +465,7 @@ struct pci_eject_response { > > > u32 status; > > > } __packed; > > > > > > -static int pci_ring_size = (4 * PAGE_SIZE); > > > +static int pci_ring_size = VMBUS_RING_SIZE(SZ_16K); > > > > > > /* > > > * Driver specific state. > > > > > > > Hi, > > > > You forgot to add #include <linux/sizes.h> for it. > > > > With that fixed: > > > > Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com> > > > > Fixed in v3. I mis-interpreted your previous comment about > adding the #include "if needed". It's not needed to compile > correctly, as sizes.h is indirectly included through some other > #include. But it's better to directly #include what's needed > lest some unrelated change cause a failure. Yes, we try include the headers we use in the .c file. I used "if needed" because I didn't check if it was already among the #includes in the file. Our tools are lacking to enforce/check a file has correct set of #includes so it's currently based mostly on reviewers noticing something is wrong with #includes, hopefully some time in the future, the tools also catch up.
diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c index 1eaffff40b8d..baadc1e5090e 100644 --- a/drivers/pci/controller/pci-hyperv.c +++ b/drivers/pci/controller/pci-hyperv.c @@ -465,7 +465,7 @@ struct pci_eject_response { u32 status; } __packed; -static int pci_ring_size = (4 * PAGE_SIZE); +static int pci_ring_size = VMBUS_RING_SIZE(SZ_16K); /* * Driver specific state.