linux-kernel - Re: [PATCH] iommu/vt-d: Fix the size calculation of pasid table

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Message-ID: <20160919121827.GB3541@8bytes.org>
Date:   Mon, 19 Sep 2016 14:18:27 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Xunlei Pang <xlpang@...hat.com>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] iommu/vt-d: Fix the size calculation of pasid table

[Cc'ing David]

On Mon, Sep 12, 2016 at 10:49:11AM +0800, Xunlei Pang wrote:
> According to the vt-d spec, the size of pasid (state) entry is 8B
> which equals 3 in power of 2, the number of pasid (state) entries
> is (ecap_pss + 1) in power of 2.
> 
> Thus the right size of pasid (state) table in power of 2 should be
> ecap_pss(iommu->ecap) plus "1+3=4" other than 7.
> 
> Signed-off-by: Xunlei Pang <xlpang@...hat.com>
> ---
>  drivers/iommu/intel-svm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel-svm.c b/drivers/iommu/intel-svm.c
> index 8ebb353..cfa75c2 100644
> --- a/drivers/iommu/intel-svm.c
> +++ b/drivers/iommu/intel-svm.c
> @@ -39,7 +39,7 @@ int intel_svm_alloc_pasid_tables(struct intel_iommu *iommu)
>  	struct page *pages;
>  	int order;
>  
> -	order = ecap_pss(iommu->ecap) + 7 - PAGE_SHIFT;
> +	order = ecap_pss(iommu->ecap) + 4 - PAGE_SHIFT;
>  	if (order < 0)
>  		order = 0;

The patch seems to be correct, but I'll let David comment on it first.



	Joerg