linux-kernel - Re: [PATCH] iommu/vt-d: Fix PASID directory pointer coherency

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Date:   Sat, 4 Feb 2023 11:43:01 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>, iommu@...ts.linux.dev,
        Joerg Roedel <joro@...tes.org>
Cc:     baolu.lu@...ux.intel.com, David Woodhouse <dwmw2@...radead.org>,
        Raj Ashok <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        stable@...r.kernel.org, Sukumar Ghorai <sukumar.ghorai@...el.com>
Subject: Re: [PATCH] iommu/vt-d: Fix PASID directory pointer coherency

On 2023/2/4 6:07, Jacob Pan wrote:
> 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.

Thanks for the fix.

> This patch adds a clflush when activating a PASID table directory.
> There's no need to do clflush of 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.
> 
> [    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@...r.kernel.org>
> Reported-by: Sukumar Ghorai <sukumar.ghorai@...el.com>
> Signed-off-by: Ashok Raj <ashok.raj@...el.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>

Add a Fixes tag so that people know how far this fix should be back
ported.

> ---
>   drivers/iommu/intel/iommu.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 59df7e42fd53..b4878c7ac008 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -1976,6 +1976,12 @@ 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);
> +		/*
> +		 * Scalable-mode PASID directory pointer is not snooped if the
> +		 * coherent bit is not set.
> +		 */
> +		if (!ecap_coherent(iommu->ecap))
> +			clflush_cache_range(table->table, sizeof(void *));

This isn't comprehensive. The clflush should be called whenever the
pasid directory table is allocated or updated.

>   
>   		/* Setup the RID_PASID field: */
>   		context_set_sm_rid2pasid(context, PASID_RID2PASID);

Best regards,
baolu