2022-03-28 21:28:03

by Jonathan Marek

Subject: [PATCH] drm/msm: use orig_nents to iterate over scatterlist with per-process tables

This matches the implementation of iommu_map_sgtable() used for the
non-per-process page tables path.

This works around the dma_map_sgtable() call (used to invalidate cache)
overwriting sgt->nents with 1 (which is probably a separate issue).

Fixes: b145c6e65eb0 ("drm/msm: Add support to create a local pagetable")
Signed-off-by: Jonathan Marek <[email protected]>
---
drivers/gpu/drm/msm/msm_iommu.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/msm_iommu.c b/drivers/gpu/drm/msm/msm_iommu.c
index bcaddbba564df..22935ef26a3a1 100644
--- a/drivers/gpu/drm/msm/msm_iommu.c
+++ b/drivers/gpu/drm/msm/msm_iommu.c
@@ -58,7 +58,7 @@ static int msm_iommu_pagetable_map(struct msm_mmu *mmu, u64 iova,
u64 addr = iova;
unsigned int i;

- for_each_sg(sgt->sgl, sg, sgt->nents, i) {
+ for_each_sg(sgt->sgl, sg, sgt->orig_nents, i) {
size_t size = sg->length;
phys_addr_t phys = sg_phys(sg);

--
2.26.1

2022-04-06 12:55:23

by Robin Murphy

Subject: Re: [PATCH] drm/msm: use orig_nents to iterate over scatterlist with per-process tables

On 2022-03-28 13:55, Jonathan Marek wrote:
> This matches the implementation of iommu_map_sgtable() used for the
> non-per-process page tables path.
>
> This works around the dma_map_sgtable() call (used to invalidate cache)
> overwriting sgt->nents with 1 (which is probably a separate issue).

FWIW that's expected behaviour. The sgtable APIs use nents to keep track
of the number of DMA segments, while orig_nents represents the physical
segments. IIUC you're not actually using the DMA mapping, just relying
on its side-effects, so it's still the physical segments that you care
about for your private IOMMU mapping here.

> Fixes: b145c6e65eb0 ("drm/msm: Add support to create a local pagetable")
> Signed-off-by: Jonathan Marek <[email protected]>
> ---
> drivers/gpu/drm/msm/msm_iommu.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_iommu.c b/drivers/gpu/drm/msm/msm_iommu.c
> index bcaddbba564df..22935ef26a3a1 100644
> --- a/drivers/gpu/drm/msm/msm_iommu.c
> +++ b/drivers/gpu/drm/msm/msm_iommu.c
> @@ -58,7 +58,7 @@ static int msm_iommu_pagetable_map(struct msm_mmu *mmu, u64 iova,
> u64 addr = iova;
> unsigned int i;
>
> - for_each_sg(sgt->sgl, sg, sgt->nents, i) {
> + for_each_sg(sgt->sgl, sg, sgt->orig_nents, i) {

Even better would be to use for_each_sgtable_sg(), which exists
primarily for the sake of avoiding this exact confusion.

Robin.

> size_t size = sg->length;
> phys_addr_t phys = sg_phys(sg);
>