Re: [PATCH] iommu/arm-smmu-v3: avoid over allocating for l2 stream tables

[Will Deacon]

Hi Nate,

On Mon, Dec 19, 2016 at 03:26:40PM -0500, Nate Watterson wrote:
> Currently, all l2 stream tables are being allocated with space for
> (1< physically supports. To avoid allocating memory for inaccessible
> stes, this patch limits the span of an l2 table to be no larger
> than the sid size of the smmu to which it belongs.
> 
> Signed-off-by: Nate Watterson 
> ---
>  drivers/iommu/arm-smmu-v3.c | 10 +++---
>  1 file changed, 7 insertions(+), 3 deletions(-)

I can't help but think you'd be better off using a linear stream table
in this scenario. If we hack the feature check for
ARM_SMMU_FEAT_2_LVL_STRTAB so that it doesn't report support for 2 level
tables if the number of sids is less than that covered by a single l2
entry, would that solve your problem?

Will

[PATCH] iommu/arm-smmu-v3: avoid over allocating for l2 stream tables

[Nate Watterson]

Currently, all l2 stream tables are being allocated with space for
(1<
---
 drivers/iommu/arm-smmu-v3.c | 10 +++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 4d6ec44..5dca671 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -1129,6 +1129,7 @@ static void arm_smmu_init_bypass_stes(u64 *strtab, 
unsigned int nent)
 
 static int arm_smmu_init_l2_strtab(struct arm_smmu_device *smmu, u32 sid)
 {
+   u8 span;
size_t size;
void *strtab;
struct arm_smmu_strtab_cfg *cfg = &smmu->strtab_cfg;
@@ -1137,10 +1138,11 @@ static int arm_smmu_init_l2_strtab(struct 
arm_smmu_device *smmu, u32 sid)
if (desc->l2ptr)
return 0;
 
-   size = 1 << (STRTAB_SPLIT + ilog2(STRTAB_STE_DWORDS) + 3);
+   span = (smmu->sid_bits < STRTAB_SPLIT) ? smmu->sid_bits : STRTAB_SPLIT;
+   size = 1 << (span + ilog2(STRTAB_STE_DWORDS) + 3);
strtab = &cfg->strtab[(sid >> STRTAB_SPLIT) * STRTAB_L1_DESC_DWORDS];
 
-   desc->span = STRTAB_SPLIT + 1;
+   desc->span = span + 1;
desc->l2ptr = dmam_alloc_coherent(smmu->dev, size, &desc->l2ptr_dma,
  GFP_KERNEL | __GFP_ZERO);
if (!desc->l2ptr) {
@@ -1150,7 +1152,7 @@ static int arm_smmu_init_l2_strtab(struct arm_smmu_device 
*smmu, u32 sid)
return -ENOMEM;
}
 
-   arm_smmu_init_bypass_stes(desc->l2ptr, 1 << STRTAB_SPLIT);
+   arm_smmu_init_bypass_stes(desc->l2ptr, 1 << span);
arm_smmu_write_strtab_l1_desc(strtab, desc);
return 0;
 }
@@ -2001,6 +2003,8 @@ static int arm_smmu_init_strtab_2lvl(struct 
arm_smmu_device *smmu)
dev_warn(smmu->dev,
 "2-level strtab only covers %u/%u bits of SID\n",
 size, smmu->sid_bits);
+   else if (smmu->sid_bits < size)
+   size = smmu->sid_bits;
 
l1size = cfg->num_l1_ents * (STRTAB_L1_DESC_DWORDS << 3);
strtab = dmam_alloc_coherent(smmu->dev, l1size, &cfg->strtab_dma,
-- 
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Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux
Foundation Collaborative Project.