linux-kernel - Re: [PATCH v2 02/10] iommu/vt-d: Fix CPU and IOMMU SVM feature matching checks

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Message-ID: <20191119093231.65fb3b3f@jacob-builder>
Date:   Tue, 19 Nov 2019 09:32:31 -0800
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Auger Eric <eric.auger@...hat.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v2 02/10] iommu/vt-d: Fix CPU and IOMMU SVM feature
 matching checks

On Tue, 19 Nov 2019 09:02:26 +0100
Auger Eric <eric.auger@...hat.com> wrote:

> Hi Jacob,
> 
> On 11/18/19 10:47 PM, Jacob Pan wrote:
> > On Mon, 18 Nov 2019 21:33:34 +0100
> > Auger Eric <eric.auger@...hat.com> wrote:
> >   
> >> Hi Jacob,
> >>
> >> On 11/18/19 8:42 PM, Jacob Pan wrote:  
> >>> The current code checks CPU and IOMMU feature set for SVM support
> >>> but the result is never stored nor used. Therefore, SVM can still
> >>> be used even when these checks failed.    
> >> "SVM can still be used even when these checks failed". What were
> >> the consequences if it happened? Does it fix this cleanly now.  
> >>>  
> > The consequence is DMA cannot reach above 48-bit virtual address
> > range when CPU does 5-level and IOMMU can only do 4-level. With is
> > fix, svm_bind_mm will fail in the first place to prevent SVM use by
> > DMA.  
> OK thank you for the clarification. Maybe this latter can be added in
> the commit message
> >
Yes, will do.   
>  [...]  
> >> nit: is it really an error or just a warning?  
> > I think it is an error in that there is an illegal configuration.
> > It is mostly for vIOMMU, we expect native HW should have these
> > features matched.  
> 
> OK
> 
> Thanks
> 
> Eric
> >   
>  [...]  
> >> Besides,
> >> Reviewed-by: Eric Auger <eric.auger@...hat.com>
> >>
> >> Thanks
> >>
> >> Eric
> >>  
> > 
> > [Jacob Pan]
> >   
> 

[Jacob Pan]