linux-kernel - Re: [PATCH v3 1/2] iommu/vt-d: Add helper to flush caches for context change

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Date: Tue, 2 Jul 2024 12:51:12 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: "Tian, Kevin" <kevin.tian@...el.com>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Jason Gunthorpe <jgg@...pe.ca>
Cc: baolu.lu@...ux.intel.com, "iommu@...ts.linux.dev"
 <iommu@...ts.linux.dev>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] iommu/vt-d: Add helper to flush caches for context
 change

On 2024/7/2 10:43, Baolu Lu wrote:
> On 7/2/24 9:47 AM, Baolu Lu wrote:
>> On 7/2/24 9:11 AM, Tian, Kevin wrote:
>>>> From: Lu Baolu<baolu.lu@...ux.intel.com>
>>>> Sent: Monday, July 1, 2024 7:23 PM
>>>> +
>>>> +    /*
>>>> +     * For scalable mode:
>>>> +     * - Domain-selective PASID-cache invalidation to affected domains
>>>> +     * - Domain-selective IOTLB invalidation to affected domains
>>>> +     * - Global Device-TLB invalidation to affected functions
>>>> +     */
>>>> +    if (flush_domains) {
>>>> +        /*
>>>> +         * If the IOMMU is running in scalable mode and there might
>>>> +         * be potential PASID translations, the caller should hold
>>>> +         * the lock to ensure that context changes and cache flushes
>>>> +         * are atomic.
>>>> +         */
>>>> +        assert_spin_locked(&iommu->lock);
>>>> +        for (i = 0; i < info->pasid_table->max_pasid; i++) {
>>>> +            pte = intel_pasid_get_entry(info->dev, i);
>>>> +            if (!pte || !pasid_pte_is_present(pte))
>>>> +                continue;
>>>> +
>>>> +            did = pasid_get_domain_id(pte);
>>>> +            qi_flush_pasid_cache(iommu, did,
>>>> QI_PC_ALL_PASIDS, 0);
>>>> +            iommu->flush.flush_iotlb(iommu, did, 0, 0,
>>>> DMA_TLB_DSI_FLUSH);
>>>> +        }
>>>> +    }
>>>> +
>>>> +    __context_flush_dev_iotlb(info);
>>>> +}
>>> this only invalidates devtlb w/o PASID. We miss a pasid devtlb 
>>> invalidation
>>> with global bit set.
>>
>> I am not sure about this. The spec says "Global Device-TLB invalidation
>> to affected functions", I am not sure whether this implies any PASID-
>> based-Device-TLB invalidation.
> 
> I just revisited the spec, Device-TLB invalidation only covers caches
> for requests-without-PASID. If pasid translation is affected while
> updating the context entry, we should also take care of the caches for
> requests-with-pasid.
> 
> I will add below line to address this.
> 
> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
> index 9a7b5668c723..91db0876682e 100644
> --- a/drivers/iommu/intel/pasid.c
> +++ b/drivers/iommu/intel/pasid.c
> @@ -932,6 +932,7 @@ void intel_context_flush_present(struct 
> device_domain_info *info,
>                          did = pasid_get_domain_id(pte);
>                          qi_flush_pasid_cache(iommu, did, 
> QI_PC_ALL_PASIDS, 0);
>                          iommu->flush.flush_iotlb(iommu, did, 0, 0, 
> DMA_TLB_DSI_FLUSH);
> +                       pasid_cache_invalidation_with_pasid(iommu, did, i);

Should be

	devtlb_invalidation_with_pasid(iommu, info->dev, i);

Sorry for the typo.

Best regards,
baolu