linux-kernel - Re: [PATCH v4 05/11] iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm exit

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Date:   Thu, 10 Feb 2022 08:27:50 -0800
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        iommu@...ts.linux-foundation.org, x86 <x86@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 05/11] iommu/sva: Assign a PASID to mm on PASID
 allocation and free it on mm exit

Hi, Jacob,

On Wed, Feb 09, 2022 at 07:16:14PM -0800, Jacob Pan wrote:
> Hi Fenghua,
> 
> On Mon,  7 Feb 2022 15:02:48 -0800, Fenghua Yu <fenghua.yu@...el.com> wrote:
> 
> > @@ -1047,8 +1040,6 @@ struct iommu_sva *intel_svm_bind(struct device
> > *dev, struct mm_struct *mm, void }
> >  
> >  	sva = intel_svm_bind_mm(iommu, dev, mm, flags);
> > -	if (IS_ERR_OR_NULL(sva))
> > -		intel_svm_free_pasid(mm);
> If bind fails, the PASID has no IOMMU nor CPU context. It should be safe to
> free here.

The PASID can not be freed even if bind fails. The PASID allocated earlier
(either in this thread or in another thread) might be populated to other
threads already and being used now.

Without freeing the PASID on bind failure, the worst case is the PASID might
not be used in the process (and will be freed on process exit anyway).

This all matches with the PASID life time described in the commit message.

Thanks.

-Fenghua