From: Ionut Nechita <ionut.nechita@windriver.com>
After the previous commit, dma_opt_mapping_size() returns 0 when no DMA
backend provides an optimal mapping size hint (e.g. IOMMU in passthrough
mode with no ops->opt_mapping_size callback).
The NVMe PCI driver used min_t(u32, NVME_MAX_BYTES >> SECTOR_SHIFT,
dma_opt_mapping_size() >> 9) to cap max_hw_sectors. With a 0 return
value this would set max_hw_sectors to 0, which is invalid.
Guard the min_t so that max_hw_sectors is only capped when
dma_opt_mapping_size() provides a real hint. When it returns 0, fall
back to the existing NVME_MAX_BYTES >> SECTOR_SHIFT default.
Fixes: 3710e2b056cb ("nvme-pci: clamp max_hw_sectors based on DMA optimized limitation")
Cc: stable@vger.kernel.org
Signed-off-by: Ionut Nechita <ionut.nechita@windriver.com>
---
drivers/nvme/host/pci.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index b78ba239c8ea8..dc148fb6eff28 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -3640,6 +3640,7 @@ static struct nvme_dev *nvme_pci_alloc_dev(struct pci_dev *pdev,
{
unsigned long quirks = id->driver_data;
int node = dev_to_node(&pdev->dev);
+ size_t dma_opt;
struct nvme_dev *dev;
struct quirk_entry *qentry;
int ret = -ENOMEM;
@@ -3691,12 +3692,16 @@ static struct nvme_dev *nvme_pci_alloc_dev(struct pci_dev *pdev,
dma_set_max_seg_size(&pdev->dev, 0xffffffff);
/*
- * Limit the max command size to prevent iod->sg allocations going
- * over a single page.
+ * Limit the max command size to prevent iod->sg allocations
+ * going over a single page. Only apply the DMA optimal mapping
+ * size limit when the DMA layer actually provides one (non-zero
+ * return from dma_opt_mapping_size()).
*/
- dev->ctrl.max_hw_sectors = min_t(u32,
- NVME_MAX_BYTES >> SECTOR_SHIFT,
- dma_opt_mapping_size(&pdev->dev) >> 9);
+ dev->ctrl.max_hw_sectors = NVME_MAX_BYTES >> SECTOR_SHIFT;
+ dma_opt = dma_opt_mapping_size(&pdev->dev);
+ if (dma_opt)
+ dev->ctrl.max_hw_sectors =
+ min_t(u32, dev->ctrl.max_hw_sectors, dma_opt >> 9);
dev->ctrl.max_segments = NVME_MAX_SEGS;
dev->ctrl.max_integrity_segments = 1;
return dev;
--
2.53.0On Mon, Mar 16, 2026 at 10:39:56PM +0200, Ionut Nechita (Wind River) wrote: > From: Ionut Nechita <ionut.nechita@windriver.com> > > After the previous commit, dma_opt_mapping_size() returns 0 when no DMA > backend provides an optimal mapping size hint (e.g. IOMMU in passthrough > mode with no ops->opt_mapping_size callback). > > The NVMe PCI driver used min_t(u32, NVME_MAX_BYTES >> SECTOR_SHIFT, > dma_opt_mapping_size() >> 9) to cap max_hw_sectors. With a 0 return > value this would set max_hw_sectors to 0, which is invalid. ... which means that if you want to change it, you need to combine both patches into one to not create a regression.
On 16/03/2026 20:39, Ionut Nechita (Wind River) wrote:
> From: Ionut Nechita <ionut.nechita@windriver.com>
>
> After the previous commit, dma_opt_mapping_size() returns 0 when no DMA
> backend provides an optimal mapping size hint (e.g. IOMMU in passthrough
> mode with no ops->opt_mapping_size callback).
>
> The NVMe PCI driver used min_t(u32, NVME_MAX_BYTES >> SECTOR_SHIFT,
> dma_opt_mapping_size() >> 9) to cap max_hw_sectors. With a 0 return
> value this would set max_hw_sectors to 0, which is invalid.
With the first patch you have introduced a temporary breakage.
>
> Guard the min_t so that max_hw_sectors is only capped when
> dma_opt_mapping_size() provides a real hint. When it returns 0, fall
> back to the existing NVME_MAX_BYTES >> SECTOR_SHIFT default.
>
> Fixes: 3710e2b056cb ("nvme-pci: clamp max_hw_sectors based on DMA optimized limitation")
> Cc: stable@vger.kernel.org
> Signed-off-by: Ionut Nechita <ionut.nechita@windriver.com>
> ---
> drivers/nvme/host/pci.c | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index b78ba239c8ea8..dc148fb6eff28 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -3640,6 +3640,7 @@ static struct nvme_dev *nvme_pci_alloc_dev(struct pci_dev *pdev,
> {
> unsigned long quirks = id->driver_data;
> int node = dev_to_node(&pdev->dev);
> + size_t dma_opt;
> struct nvme_dev *dev;
> struct quirk_entry *qentry;
> int ret = -ENOMEM;
> @@ -3691,12 +3692,16 @@ static struct nvme_dev *nvme_pci_alloc_dev(struct pci_dev *pdev,
> dma_set_max_seg_size(&pdev->dev, 0xffffffff);
>
> /*
> - * Limit the max command size to prevent iod->sg allocations going
> - * over a single page.
> + * Limit the max command size to prevent iod->sg allocations
> + * going over a single page. Only apply the DMA optimal mapping
> + * size limit when the DMA layer actually provides one (non-zero
> + * return from dma_opt_mapping_size()).
> */
> - dev->ctrl.max_hw_sectors = min_t(u32,
> - NVME_MAX_BYTES >> SECTOR_SHIFT,
> - dma_opt_mapping_size(&pdev->dev) >> 9);
> + dev->ctrl.max_hw_sectors = NVME_MAX_BYTES >> SECTOR_SHIFT;
> + dma_opt = dma_opt_mapping_size(&pdev->dev);
> + if (dma_opt)
> + dev->ctrl.max_hw_sectors =
> + min_t(u32, dev->ctrl.max_hw_sectors, dma_opt >> 9);
SECTOR_SHIFT can be used instead of hard-coded '9'
> dev->ctrl.max_segments = NVME_MAX_SEGS;
> dev->ctrl.max_integrity_segments = 1;
> return dev;
On 3/17/26 05:39, Ionut Nechita (Wind River) wrote:
> From: Ionut Nechita <ionut.nechita@windriver.com>
>
> After the previous commit, dma_opt_mapping_size() returns 0 when no DMA
> backend provides an optimal mapping size hint (e.g. IOMMU in passthrough
> mode with no ops->opt_mapping_size callback).
>
> The NVMe PCI driver used min_t(u32, NVME_MAX_BYTES >> SECTOR_SHIFT,
> dma_opt_mapping_size() >> 9) to cap max_hw_sectors. With a 0 return
> value this would set max_hw_sectors to 0, which is invalid.
>
> Guard the min_t so that max_hw_sectors is only capped when
> dma_opt_mapping_size() provides a real hint. When it returns 0, fall
> back to the existing NVME_MAX_BYTES >> SECTOR_SHIFT default.
>
> Fixes: 3710e2b056cb ("nvme-pci: clamp max_hw_sectors based on DMA optimized limitation")
> Cc: stable@vger.kernel.org
> Signed-off-by: Ionut Nechita <ionut.nechita@windriver.com>
> ---
> drivers/nvme/host/pci.c | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index b78ba239c8ea8..dc148fb6eff28 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -3640,6 +3640,7 @@ static struct nvme_dev *nvme_pci_alloc_dev(struct pci_dev *pdev,
> {
> unsigned long quirks = id->driver_data;
> int node = dev_to_node(&pdev->dev);
> + size_t dma_opt;
> struct nvme_dev *dev;
> struct quirk_entry *qentry;
> int ret = -ENOMEM;
> @@ -3691,12 +3692,16 @@ static struct nvme_dev *nvme_pci_alloc_dev(struct pci_dev *pdev,
> dma_set_max_seg_size(&pdev->dev, 0xffffffff);
>
> /*
> - * Limit the max command size to prevent iod->sg allocations going
> - * over a single page.
> + * Limit the max command size to prevent iod->sg allocations
> + * going over a single page. Only apply the DMA optimal mapping
> + * size limit when the DMA layer actually provides one (non-zero
> + * return from dma_opt_mapping_size()).
> */
> - dev->ctrl.max_hw_sectors = min_t(u32,
> - NVME_MAX_BYTES >> SECTOR_SHIFT,
> - dma_opt_mapping_size(&pdev->dev) >> 9);
Why not simply change this to min_not_zero() ? That would do the same. Are you
maybe getting a warning without the u32 cast ?
> + dev->ctrl.max_hw_sectors = NVME_MAX_BYTES >> SECTOR_SHIFT;
> + dma_opt = dma_opt_mapping_size(&pdev->dev);
> + if (dma_opt)
> + dev->ctrl.max_hw_sectors =
> + min_t(u32, dev->ctrl.max_hw_sectors, dma_opt >> 9);
> dev->ctrl.max_segments = NVME_MAX_SEGS;
> dev->ctrl.max_integrity_segments = 1;
> return dev;
--
Damien Le Moal
Western Digital Research
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