linux-kernel - Re: [PATCH 3/7] iommu/vt-d: Fix PASID devTLB invalidation

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Message-ID: <57091f4a-fb53-40a4-6a28-a498f548f8b8@linux.intel.com>
Date:   Thu, 25 Jun 2020 15:25:57 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>
Cc:     baolu.lu@...ux.intel.com, Yi Liu <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Eric Auger <eric.auger@...hat.com>
Subject: Re: [PATCH 3/7] iommu/vt-d: Fix PASID devTLB invalidation

On 2020/6/23 23:43, Jacob Pan wrote:
> DevTLB flush can be used for both DMA request with and without PASIDs.
> The former uses PASID#0 (RID2PASID), latter uses non-zero PASID for SVA
> usage.
> 
> This patch adds a check for PASID value such that devTLB flush with
> PASID is used for SVA case. This is more efficient in that multiple
> PASIDs can be used by a single device, when tearing down a PASID entry
> we shall flush only the devTLB specific to a PASID.
> 
> Fixes: 6f7db75e1c46 ("iommu/vt-d: Add second level page table")
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> ---
>   drivers/iommu/intel/pasid.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
> index c81f0f17c6ba..3991a24539a1 100644
> --- a/drivers/iommu/intel/pasid.c
> +++ b/drivers/iommu/intel/pasid.c
> @@ -486,7 +486,16 @@ devtlb_invalidation_with_pasid(struct intel_iommu *iommu,
>   	qdep = info->ats_qdep;
>   	pfsid = info->pfsid;
>   
> -	qi_flush_dev_iotlb(iommu, sid, pfsid, qdep, 0, 64 - VTD_PAGE_SHIFT);
> +	/*
> +	 * When PASID 0 is used, it indicates RID2PASID(DMA request w/o PASID),
> +	 * devTLB flush w/o PASID should be used. For non-zero PASID under
> +	 * SVA usage, device could do DMA with multiple PASIDs. It is more
> +	 * efficient to flush devTLB specific to the PASID.
> +	 */
> +	if (pasid)

How about

	if (pasid == PASID_RID2PASID)
		qi_flush_dev_iotlb(iommu, sid, pfsid, qdep, 0, 64 - VTD_PAGE_SHIFT);
	else
		qi_flush_dev_iotlb_pasid(iommu, sid, pfsid, pasid, qdep, 0, 64 - 
VTD_PAGE_SHIFT);

?

It makes the code more readable and still works even we reassign another
pasid for RID2PASID.

Best regards,
baolu

> +		qi_flush_dev_iotlb_pasid(iommu, sid, pfsid, pasid, qdep, 0, 64 - VTD_PAGE_SHIFT);
> +	else
> +		qi_flush_dev_iotlb(iommu, sid, pfsid, qdep, 0, 64 - VTD_PAGE_SHIFT);
>   }
>   
>   void intel_pasid_tear_down_entry(struct intel_iommu *iommu, struct device *dev,
>