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Date:   Mon, 15 Jun 2020 09:52:02 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Fenghua Yu <fenghua.yu@intel.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        H Peter Anvin <hpa@zytor.com>,
        David Woodhouse <dwmw2@infradead.org>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        Frederic Barrat <fbarrat@linux.ibm.com>,
        Andrew Donnellan <ajd@linux.ibm.com>,
        Felix Kuehling <Felix.Kuehling@amd.com>,
        Joerg Roedel <joro@8bytes.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Jacob Jun Pan <jacob.jun.pan@intel.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Yu-cheng Yu <yu-cheng.yu@intel.com>,
        Sohil Mehta <sohil.mehta@intel.com>,
        Ravi V Shankar <ravi.v.shankar@intel.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        x86 <x86@kernel.org>, iommu@lists.linux-foundation.org,
        amd-gfx <amd-gfx@lists.freedesktop.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH v2 00/12] x86: tag application address space for devices
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On Fri, Jun 12, 2020 at 05:41:21PM -0700, Fenghua Yu wrote:

> This series only provides simple and basic support for ENQCMD and the MSR:
> 1. Clean up type definitions (patch 1-3). These patches can be in a
>    separate series.
>    - Define "pasid" as "unsigned int" consistently (patch 1 and 2).
>    - Define "flags" as "unsigned int"
> 2. Explain different various technical terms used in the series (patch 4).
> 3. Enumerate support for ENQCMD in the processor (patch 5).
> 4. Handle FPU PASID state and the MSR during context switch (patches 6-7).
> 5. Define "pasid" in mm_struct (patch 8).
> 5. Clear PASID state for new mm and forked and cloned thread (patch 9-10).
> 6. Allocate and free PASID for a process (patch 11).
> 7. Fix up the PASID MSR in #GP handler when one thread in a process
>    executes ENQCMD for the first time (patches 12).

If this is per mm, should not switch_mm() update the MSR ? I'm not
seeing that, nor do I see it explained why not.