On Mon, 12 Feb 2024, mhkelley58@xxxxxxxxx wrote: > From: Michael Kelley <mhklinux@xxxxxxxxxxx> > > 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@xxxxxxxxxxxxxxx> # 5.15.x > Signed-off-by: Michael Kelley <mhklinux@xxxxxxxxxxx> > --- > 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..5f22ad38bb98 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(16 * 1024); SZ_16K (and add the relevant #include if needed). -- i.