From: Jacob Pan <jacob.jun.pan@intel.com>
To: Fenghua Yu <fenghua.yu@intel.com>
Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>,
Joerg Roedel <joro@8bytes.org>,
Lu Baolu <baolu.lu@linux.intel.com>,
Ashok Raj <ashok.raj@intel.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
<iommu@lists.linux-foundation.org>, <zhangfei.gao@foxmail.com>,
<linux-mm@kvack.org>,
jacob.jun.pan@intel.com
Subject: Re: [PATCH v6 08/12] fork: Clear PASID for new mm
Date: Mon, 1 Mar 2021 15:00:11 -0800 [thread overview]
Message-ID: <20210301150011.766e70a3@jacob-builder> (raw)
In-Reply-To: <YDgh53AcQHT+T3L0@otcwcpicx3.sc.intel.com>
Hi Fenghua,
On Thu, 25 Feb 2021 22:17:11 +0000, Fenghua Yu <fenghua.yu@intel.com> wrote:
> Hi, Jean,
>
> On Wed, Feb 24, 2021 at 11:19:27AM +0100, Jean-Philippe Brucker wrote:
> > Hi Fenghua,
> >
> > [Trimmed the Cc list]
> >
> > On Mon, Jul 13, 2020 at 04:48:03PM -0700, Fenghua Yu wrote:
> > > When a new mm is created, its PASID should be cleared, i.e. the PASID
> > > is initialized to its init state 0 on both ARM and X86.
> >
> > I just noticed this patch was dropped in v7, and am wondering whether we
> > could still upstream it. Does x86 need a child with a new address space
> > (!CLONE_VM) to inherit the PASID of the parent? That doesn't make much
> > sense with regard to IOMMU structures - same PASID indexing multiple
> > PGDs?
>
> You are right: x86 should clear mm->pasid when a new mm is created.
> This patch somehow is losted:(
>
> >
> > Currently iommu_sva_alloc_pasid() assumes mm->pasid is always
> > initialized to 0 and fails on forked tasks. I'm trying to figure out
> > how to fix this. Could we clear the pasid on fork or does it break the
> > x86 model?
>
> x86 calls ioasid_alloc() instead of iommu_sva_alloc_pasid(). So
We should consolidate at some point, there is no need to store pasid in two
places.
> 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. 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?
>
> Thanks.
>
> -Fenghua
Thanks,
Jacob
prev parent reply other threads:[~2021-03-01 22:58 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1594684087-61184-1-git-send-email-fenghua.yu@intel.com>
[not found] ` <1594684087-61184-9-git-send-email-fenghua.yu@intel.com>
2021-02-24 10:19 ` [PATCH v6 08/12] fork: Clear PASID for new mm Jean-Philippe Brucker
2021-02-25 22:17 ` Fenghua Yu
2021-03-01 23:00 ` Jacob Pan [this message]
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