The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
Thanks, Sasha
------------------ original commit in Linus's tree ------------------
From b5ff74c1ef50fe08e384026875fec660fadfaedd Mon Sep 17 00:00:00 2001 From: Michael Kelley mhklinux@outlook.com Date: Fri, 16 Feb 2024 12:22:40 -0800 Subject: [PATCH] PCI: hv: Fix ring buffer size calculation MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit
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.
Link: https://lore.kernel.org/linux-pci/20240216202240.251818-1-mhklinux@outlook.c... Signed-off-by: Michael Kelley mhklinux@outlook.com Signed-off-by: Krzysztof Wilczyński kwilczynski@kernel.org Reviewed-by: Kuppuswamy Sathyanarayanan sathyanarayanan.kuppuswamy@linux.intel.com Reviewed-by: Ilpo Jarvinen ilpo.jarvinen@linux.intel.com Reviewed-by: Long Li longli@microsoft.com Cc: stable@vger.kernel.org # 5.15.x --- drivers/pci/controller/pci-hyperv.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c index 1eaffff40b8d4..5992280e8110b 100644 --- a/drivers/pci/controller/pci-hyperv.c +++ b/drivers/pci/controller/pci-hyperv.c @@ -49,6 +49,7 @@ #include <linux/refcount.h> #include <linux/irqdomain.h> #include <linux/acpi.h> +#include <linux/sizes.h> #include <asm/mshyperv.h>
/* @@ -465,7 +466,7 @@ 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.