linux-kernel - [PATCH] nvme-pci: 512 byte aligned dma pool segment quirk

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Message-ID: <20241112195053.3939762-1-bob.beckett@collabora.com>
Date: Tue, 12 Nov 2024 19:50:00 +0000
From: Bob Beckett <bob.beckett@...labora.com>
To: Keith Busch <kbusch@...nel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Christoph Hellwig <hch@....de>,
	Sagi Grimberg <sagi@...mberg.me>
Cc: kernel@...labora.com,
	Robert Beckett <bob.beckett@...labora.com>,
	linux-nvme@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] nvme-pci: 512 byte aligned dma pool segment quirk

From: Robert Beckett <bob.beckett@...labora.com>

We initially put in a quick fix of limiting the queue depth to 1
as experimentation showed that it fixed data corruption on 64GB
steamdecks.

After further experimentation, it appears that the corruption
is fixed by aligning the small dma pool segments to 512 bytes.
Testing via desync image verification shows that it now passes
thousands of verification loops, where previously
it never managed above 7.

Currently it is not known why this fixes the corruption.
Perhaps it is doing something nasty like using an mmc page
as a cache for the prp lists (mmc min. page size is 512 bytes)
and not invalidating properly, so that the dma pool change to
treats segment list as a stack ends up giving a previous
segment in the same cached page.

This fixes the previous queue depth limitation as it fixes
the corruption without incurring a 37% tested performance
degredation.

Fixes: 83bdfcbdbe5d ("nvme-pci: qdepth 1 quirk")
Signed-off-by: Robert Beckett <bob.beckett@...labora.com>
---
 drivers/nvme/host/nvme.h | 5 +++++
 drivers/nvme/host/pci.c  | 6 +++---
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 093cb423f536..61bba5513de0 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -173,6 +173,11 @@ enum nvme_quirks {
 	 * MSI (but not MSI-X) interrupts are broken and never fire.
 	 */
 	NVME_QUIRK_BROKEN_MSI			= (1 << 21),
+
+	/*
+	 * Align dma pool segment size to 512 bytes
+	 */
+	NVME_QUIRK_DMAPOOL_ALIGN_512		= (1 << 22),
 };
 
 /*
diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 4b9fda0b1d9a..6fcd3bb413c4 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -2700,8 +2700,8 @@ static int nvme_setup_prp_pools(struct nvme_dev *dev)
 		return -ENOMEM;
 
 	/* Optimisation for I/Os between 4k and 128k */
-	dev->prp_small_pool = dma_pool_create("prp list 256", dev->dev,
-						256, 256, 0);
+	dev->prp_small_pool = dma_pool_create("prp list 256", dev->dev,256,
+				       dev->ctrl.quirks & NVME_QUIRK_DMAPOOL_ALIGN_512 ? 512 : 256, 0);
 	if (!dev->prp_small_pool) {
 		dma_pool_destroy(dev->prp_page_pool);
 		return -ENOMEM;
@@ -3449,7 +3449,7 @@ static const struct pci_device_id nvme_id_table[] = {
 	{ PCI_VDEVICE(REDHAT, 0x0010),	/* Qemu emulated controller */
 		.driver_data = NVME_QUIRK_BOGUS_NID, },
 	{ PCI_DEVICE(0x1217, 0x8760), /* O2 Micro 64GB Steam Deck */
-		.driver_data = NVME_QUIRK_QDEPTH_ONE },
+		.driver_data = NVME_QUIRK_DMAPOOL_ALIGN_512, },
 	{ PCI_DEVICE(0x126f, 0x2262),	/* Silicon Motion generic */
 		.driver_data = NVME_QUIRK_NO_DEEPEST_PS |
 				NVME_QUIRK_BOGUS_NID, },
-- 
2.45.2