linux-kernel - Re: [PATCH] iommu/arm-smmu-v3: Fix L1 stream table index calculation for AmpereOne

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Message-ID: <e374e8ec-29db-48a2-95d7-6fc9ac6317d9@os.amperecomputing.com>
Date: Tue, 1 Oct 2024 13:47:24 -0700
From: Yang Shi <yang@...amperecomputing.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Nicolin Chen <nicolinc@...dia.com>, will@...nel.org,
 robin.murphy@....com, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/arm-smmu-v3: Fix L1 stream table index calculation
 for AmpereOne



On 10/1/24 12:46 PM, Jason Gunthorpe wrote:
> On Tue, Oct 01, 2024 at 12:38:56PM -0700, Yang Shi wrote:
>>
>> On 10/1/24 12:18 PM, Jason Gunthorpe wrote:
>>> On Tue, Oct 01, 2024 at 12:09:03PM -0700, Yang Shi wrote:
>>>>> Also, there are other places doing "1 << smmu->sid_bits", e.g.
>>>>> arm_smmu_init_strtab_linear().
>>>> The disassembly shows it uses "sbfiz x21, x20, 6, 32" instead of lsl. 1UL
>>>> should be used if we want to take extra caution and don't prefer rely on
>>>> compiler.
>>> Still, we should be fixing them all if sid_bits == 32, all those
>>> shifts should be throwing a UBSAN error. It would be crazy to have a
>> OK, will cover this is v2.
> Maybe just make a little inline function to do this math and remove
> the repated open coding? Then the types can be right, etc.

Something like this?

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c 
b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index 01a2faee04bc..0f3aa7962117 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -3624,8 +3624,9 @@ static int arm_smmu_init_strtab_2lvl(struct 
arm_smmu_device *smmu)
  {
         u32 l1size;
         struct arm_smmu_strtab_cfg *cfg = &smmu->strtab_cfg;
+       unsigned int max_sid = arm_smmu_strtab_max_sid(smmu->sid_bits);
         unsigned int last_sid_idx =
-               arm_smmu_strtab_l1_idx((1UL << smmu->sid_bits) - 1);
+               arm_smmu_strtab_l1_idx(max_sid - 1);

         /* Calculate the L1 size, capped to the SIDSIZE. */
         cfg->l2.num_l1_ents = min(last_sid_idx + 1, STRTAB_MAX_L1_ENTRIES);
@@ -3657,8 +3658,9 @@ static int arm_smmu_init_strtab_linear(struct 
arm_smmu_device *smmu)
  {
         u32 size;
         struct arm_smmu_strtab_cfg *cfg = &smmu->strtab_cfg;
+       unsigned int max_sid = arm_smmu_strtab_max_sid(smmu->sid_bits);

-       size = (1 << smmu->sid_bits) * sizeof(struct arm_smmu_ste);
+       size = max_sid * sizeof(struct arm_smmu_ste);
         cfg->linear.table = dmam_alloc_coherent(smmu->dev, size,
&cfg->linear.ste_dma,
                                                 GFP_KERNEL);
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h 
b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
index 1e9952ca989f..de9f14293485 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
@@ -235,6 +235,11 @@ static inline u32 arm_smmu_strtab_l2_idx(u32 sid)
         return sid % STRTAB_NUM_L2_STES;
  }

+static inline unsigned int arm_smmu_strtab_max_sid(unsigned int sid_bits)
+{
+       return (1UL << sid_bits);
+}
+

>
> Jason