linux-kernel - Re: [PATCH v6 08/12] fork: Clear PASID for new mm

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Date:   Tue, 2 Mar 2021 11:43:36 +0100
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     Jacob Pan <jacob.jun.pan@...el.com>
Cc:     Fenghua Yu <fenghua.yu@...el.com>, Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Ashok Raj <ashok.raj@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        iommu@...ts.linux-foundation.org, zhangfei.gao@...mail.com,
        linux-mm@...ck.org
Subject: Re: [PATCH v6 08/12] fork: Clear PASID for new mm

On Mon, Mar 01, 2021 at 03:00:11PM -0800, Jacob Pan wrote:
> > functionality is not a problem without this patch on x86. But I think
> I feel the reason that x86 doesn't care is that mm->pasid is not used
> unless bind_mm is called.

I think vt-d also maintains the global_svm_list, that tells whether a
PASID is already allocated for the mm. The SMMU driver relies only on
iommu_sva_alloc_pasid() for this.

> For the fork children even mm->pasid is non-zero,
> it has no effect since it is not loaded onto MSRs.
> Perhaps you could also add a check or WARN_ON(!mm->pasid) in load_pasid()?
> 
> > we do need to have this patch in the kernel because PASID is per addr
> > space and two addr spaces shouldn't have the same PASID.
> > 
> Agreed.
> 
> > Who will accept this patch?

It's not clear from get_maintainers.pl, but I guess it should go via
linux-mm. Since the list wasn't cc'd on the original patch, I resent it.

Thanks,
Jean