linux-kernel - Re: [PATCH 2/5] iommu/vt-d: Fix unaligned addresses for intel_flush_svm_range

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Date:   Tue, 5 Jan 2021 19:03:58 +0000
From:   Will Deacon <will@...nel.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>, Ashok Raj <ashok.raj@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Guo Kaijie <Kaijie.Guo@...el.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] iommu/vt-d: Fix unaligned addresses for
 intel_flush_svm_range_dev()

On Thu, Dec 31, 2020 at 08:53:20AM +0800, Lu Baolu wrote:
> The VT-d hardware will ignore those Addr bits which have been masked by
> the AM field in the PASID-based-IOTLB invalidation descriptor. As the
> result, if the starting address in the descriptor is not aligned with
> the address mask, some IOTLB caches might not invalidate. Hence people
> will see below errors.
> 
> [ 1093.704661] dmar_fault: 29 callbacks suppressed
> [ 1093.704664] DMAR: DRHD: handling fault status reg 3
> [ 1093.712738] DMAR: [DMA Read] Request device [7a:02.0] PASID 2
>                fault addr 7f81c968d000 [fault reason 113]
>                SM: Present bit in first-level paging entry is clear
> 
> Fix this by using aligned address for PASID-based-IOTLB invalidation.
> 
> Fixes: 1c4f88b7f1f92 ("iommu/vt-d: Shared virtual address in scalable mode")
> Reported-and-tested-by: Guo Kaijie <Kaijie.Guo@...el.com>
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
>  drivers/iommu/intel/svm.c | 22 ++++++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
> index 69566695d032..b16a4791acfb 100644
> --- a/drivers/iommu/intel/svm.c
> +++ b/drivers/iommu/intel/svm.c
> @@ -118,8 +118,10 @@ void intel_svm_check(struct intel_iommu *iommu)
>  	iommu->flags |= VTD_FLAG_SVM_CAPABLE;
>  }
>  
> -static void intel_flush_svm_range_dev (struct intel_svm *svm, struct intel_svm_dev *sdev,
> -				unsigned long address, unsigned long pages, int ih)
> +static void __flush_svm_range_dev(struct intel_svm *svm,
> +				  struct intel_svm_dev *sdev,
> +				  unsigned long address,
> +				  unsigned long pages, int ih)
>  {
>  	struct qi_desc desc;
>  
> @@ -170,6 +172,22 @@ static void intel_flush_svm_range_dev (struct intel_svm *svm, struct intel_svm_d
>  	}
>  }
>  
> +static void intel_flush_svm_range_dev(struct intel_svm *svm,
> +				      struct intel_svm_dev *sdev,
> +				      unsigned long address,
> +				      unsigned long pages, int ih)
> +{
> +	unsigned long shift = ilog2(__roundup_pow_of_two(pages));
> +	unsigned long align = (1ULL << (VTD_PAGE_SHIFT + shift));
> +	unsigned long start = ALIGN_DOWN(address, align);
> +	unsigned long end = ALIGN(address + (pages << VTD_PAGE_SHIFT), align);
> +
> +	while (start < end) {
> +		__flush_svm_range_dev(svm, sdev, start, align >> VTD_PAGE_SHIFT, ih);
> +		start += align;
> +	}
> +}

Given that this only seems to be called from intel_invalidate_range(), which
has to compute 'pages' only to have it pulled apart again here, perhaps it
would be cleaner for intel_flush_svm_range() to take something like an
'order' argument instead?

What do you think?

Will