linux-kernel - FAILED: Patch "PCI: hv: Fix ring buffer size calculation" failed to apply to 5.15-stable tree

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Date: Wed, 27 Mar 2024 08:15:35 -0400
From: Sasha Levin <sashal@...nel.org>
To: stable@...r.kernel.org,
	mhklinux@...look.com
Cc: Krzysztof Wilczyński <kwilczynski@...nel.org>,
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
	Ilpo Jarvinen <ilpo.jarvinen@...ux.intel.com>,
	Long Li <longli@...rosoft.com>,
	linux-hyperv@...r.kernel.org,
	linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: FAILED: Patch "PCI: hv: Fix ring buffer size calculation" failed to apply to 5.15-stable tree

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@...r.kernel.org>.

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

>From b5ff74c1ef50fe08e384026875fec660fadfaedd Mon Sep 17 00:00:00 2001
From: Michael Kelley <mhklinux@...look.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.com
Signed-off-by: Michael Kelley <mhklinux@...look.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@...nel.org>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
Reviewed-by: Ilpo Jarvinen <ilpo.jarvinen@...ux.intel.com>
Reviewed-by: Long Li <longli@...rosoft.com>
Cc: <stable@...r.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.
-- 
2.43.0