linux-kernel - RE: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

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Date:   Mon, 15 Jun 2020 17:11:02 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        "Yu, Fenghua" <fenghua.yu@...el.com>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        "David Woodhouse" <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Frederic Barrat <fbarrat@...ux.ibm.com>,
        Andrew Donnellan <ajd@...ux.ibm.com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Joerg Roedel <joro@...tes.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Yu, Yu-cheng" <yu-cheng.yu@...el.com>,
        "Mehta, Sohil" <sohil.mehta@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        x86 <x86@...nel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        amd-gfx <amd-gfx@...ts.freedesktop.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: RE: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

>> The heuristic always initializes the MSR with the per mm PASID IIF the
>> mm has a valid PASID but the MSR doesn't have one. This heuristic usually
>> happens only once on the first #GP in a thread.
>
> But it doesn't guarantee the PASID is the right one. Suppose both the mm
> has a PASID and the MSR has a VALID one, but the MSR isn't the mm one.
> Then we NO-OP. So if the exception was due to us having the wrong PASID,
> we stuck.

ENQCMD only checks the 'valid' bit of the IA32_PASID MSR to decide whether
to #GP or not.  H/W has no concept of the "right" pasid value.

If IA32_PASID is valid with the wrong value ... then the system is about to
see some major corruption because the operations in the accelerator are
not going to translate to the physical addresses for pages owned by the process
that issued the ENQCMD.

-Tony