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

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Date:   Wed, 12 Oct 2016 13:17:54 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     Joerg Roedel <joro@...tes.org>, Xunlei Pang <xlpang@...hat.com>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/vt-d: Fix the size calculation of pasid table

On Mon, 2016-09-19 at 14:18 +0200, Joerg Roedel wrote:
> [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.

Yes, that looks correct. I think we may also need to limit it, because
full 20-bit PASID support means we'll attempt an order 11 allocation.
But that's certainly correct for now

Acked-by: David Woodhouse <dwmw2@...radead.org>


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dwmw2
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