linux-kernel - RE: [PATCH 1/3] iommu/vt-d: Set PGSNP bit in pasid table entry for sva binding

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Date:   Mon, 18 Apr 2022 06:56:23 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>
CC:     "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/3] iommu/vt-d: Set PGSNP bit in pasid table entry for
 sva binding

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Saturday, April 16, 2022 8:31 PM
> 
> This field make the requests snoop processor caches irrespective of other
> attributes in the request or other fields in paging structure entries
> used to translate the request. The latest VT-d specification states that
> this field is treated as Reserved(0) for implementations not supporting
> Snoop Control (SC=0 in the Extended Capability Register). Hence add a
> check in the code.
> 
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
>  drivers/iommu/intel/pasid.c | 2 +-
>  drivers/iommu/intel/svm.c   | 1 +
>  2 files changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
> index f8d215d85695..9ca3c67a2058 100644
> --- a/drivers/iommu/intel/pasid.c
> +++ b/drivers/iommu/intel/pasid.c
> @@ -625,7 +625,7 @@ int intel_pasid_setup_first_level(struct intel_iommu
> *iommu,
>  		}
>  	}
> 
> -	if (flags & PASID_FLAG_PAGE_SNOOP)
> +	if ((flags & PASID_FLAG_PAGE_SNOOP) && ecap_sc_support(iommu-
> >ecap))
>  		pasid_set_pgsnp(pte);

If the caller wants snoop for some reason is it correct to simply
ignore the request when lacking of hw support? Suppose certain
errno should be returned here...

> 
>  	pasid_set_domain_id(pte, did);
> diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
> index 23a38763c1d1..d88af37c20ef 100644
> --- a/drivers/iommu/intel/svm.c
> +++ b/drivers/iommu/intel/svm.c
> @@ -394,6 +394,7 @@ static struct iommu_sva *intel_svm_bind_mm(struct
> intel_iommu *iommu,
>  	sflags = (flags & SVM_FLAG_SUPERVISOR_MODE) ?
>  			PASID_FLAG_SUPERVISOR_MODE : 0;
>  	sflags |= cpu_feature_enabled(X86_FEATURE_LA57) ?
> PASID_FLAG_FL5LP : 0;
> +	sflags |= PASID_FLAG_PAGE_SNOOP;
>  	spin_lock_irqsave(&iommu->lock, iflags);
>  	ret = intel_pasid_setup_first_level(iommu, dev, mm->pgd, mm-
> >pasid,
>  					    FLPT_DEFAULT_DID, sflags);
> --
> 2.25.1