RE: [PATCH v3] iommu/vt-d: Fix PASID directory pointer coherency

[Tian, Kevin]

> From: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> Sent: Wednesday, April 5, 2023 11:45 PM
> 
> On platforms that do not support IOMMU Extended capability bit 0
> Page-walk Coherency, CPU caches are not snooped when IOMMU is
> accessing
> any translation structures. IOMMU access goes only directly to
> memory. Intel IOMMU code was missing a flush for the PASID table
> directory that resulted in the unrecoverable fault as shown below.
> 
> This patch adds clflush calls whenever allocating and updating
> a PASID table directory to ensure cache coherency.
> 
> On the reverse direction, there's no need to clflush the PASID directory
> pointer when we deactivate a context entry in that IOMMU hardware will
> not see the old PASID directory pointer after we clear the context entry.
> PASID directory entries are also never freed once allocated.
> 
> [    0.555386] DMAR: DRHD: handling fault status reg 3
> [    0.555805] DMAR: [DMA Read NO_PASID] Request device [00:0d.2] fault
> addr 0x1026a4000 [fault reason 0x51] SM: Present bit in Directory Entry is
> clear
> [    0.556348] DMAR: Dump dmar1 table entries for IOVA 0x1026a4000
> [    0.556348] DMAR: scalable mode root entry: hi 0x0000000102448001, low
> 0x0000000101b3e001
> [    0.556348] DMAR: context entry: hi 0x0000000000000000, low
> 0x0000000101b4d401
> [    0.556348] DMAR: pasid dir entry: 0x0000000101b4e001
> [    0.556348] DMAR: pasid table entry[0]: 0x0000000000000109
> [    0.556348] DMAR: pasid table entry[1]: 0x0000000000000001
> [    0.556348] DMAR: pasid table entry[2]: 0x0000000000000000
> [    0.556348] DMAR: pasid table entry[3]: 0x0000000000000000
> [    0.556348] DMAR: pasid table entry[4]: 0x0000000000000000
> [    0.556348] DMAR: pasid table entry[5]: 0x0000000000000000
> [    0.556348] DMAR: pasid table entry[6]: 0x0000000000000000
> [    0.556348] DMAR: pasid table entry[7]: 0x0000000000000000
> [    0.556348] DMAR: PTE not present at level 4
> 
> Cc: <stable@xxxxxxxxxxxxxxx>
> Fixes: 0bbeb01a4faf ("iommu/vt-d: Manage scalalble mode PASID tables")
> Reported-by: Sukumar Ghorai <sukumar.ghorai@xxxxxxxxx>
> Signed-off-by: Ashok Raj <ashok.raj@xxxxxxxxx>
> Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> ---
> v3: Add clflush after PASID directory allocation to prevent malicious
> device attack with unauthorized PASIDs. Also flush all the PASID entries
> after directory updates. (Baolu)
> v2: Add clflush to PASID directory update case (Baolu, Kevin review)
> ---
>  drivers/iommu/intel/iommu.c | 2 ++
>  drivers/iommu/intel/pasid.c | 7 +++++++
>  2 files changed, 9 insertions(+)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 59df7e42fd53..161342e7149d 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -1976,6 +1976,8 @@ static int domain_context_mapping_one(struct
> dmar_domain *domain,
>  		pds = context_get_sm_pds(table);
>  		context->lo = (u64)virt_to_phys(table->table) |
>  				context_pdts(pds);
> +		if (!ecap_coherent(iommu->ecap))
> +			clflush_cache_range(table->table, sizeof(u64));

v2 of this patch was already merged w/o this change.

can you elaborate the purpose of v3? Here no flush is required as long
as it's done in other two places below.

> 
>  		/* Setup the RID_PASID field: */
>  		context_set_sm_rid2pasid(context, PASID_RID2PASID);
> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
> index fb3c7020028d..979f796175b1 100644
> --- a/drivers/iommu/intel/pasid.c
> +++ b/drivers/iommu/intel/pasid.c
> @@ -128,6 +128,9 @@ int intel_pasid_alloc_table(struct device *dev)
>  	pasid_table->max_pasid = 1 << (order + PAGE_SHIFT + 3);
>  	info->pasid_table = pasid_table;
> 
> +	if (!ecap_coherent(info->iommu->ecap))
> +		clflush_cache_range(pasid_table->table, size);
> +
>  	return 0;
>  }
> 
> @@ -215,6 +218,10 @@ static struct pasid_entry
> *intel_pasid_get_entry(struct device *dev, u32 pasid)
>  			free_pgtable_page(entries);
>  			goto retry;
>  		}
> +		if (!ecap_coherent(info->iommu->ecap)) {
> +			clflush_cache_range(entries, VTD_PAGE_SIZE);
> +			clflush_cache_range(&dir[dir_index].val, sizeof(*dir));
> +		}
>  	}
> 
>  	return &entries[index];
> --
> 2.25.1