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Date:   Fri, 11 Feb 2022 16:11:03 -0800
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To:     Andy Lutomirski <luto@kernel.org>,
        Rick P Edgecombe <rick.p.edgecombe@intel.com>,
        the arch/x86 maintainers <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
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        Balbir Singh <bsingharora@gmail.com>,
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        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Eugene Syromiatnikov <esyr@redhat.com>,
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        Dave Martin <Dave.Martin@arm.com>,
        Weijiang Yang <weijiang.yang@intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
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        "john.allen@amd.com" <john.allen@amd.com>,
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        "Eranian, Stephane" <eranian@google.com>
Cc:     Yu-cheng Yu <yu-cheng.yu@intel.com>
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From:   Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCH 25/35] x86/cet/shstk: Add user-mode shadow stack support
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On 2/11/22 16:07, Andy Lutomirski wrote:
> On Fri, Feb 11, 2022, at 3:37 PM, Dave Hansen wrote:
>> On 1/30/22 13:18, Rick Edgecombe wrote:
>>> Add the user shadow stack MSRs to the xsave helpers, so they can be used
>>> to implement the functionality.
>> Do these MSRs ever affect kernel-mode operation?
>>
>> If so, we might need to switch them more aggressively at context-switch
>> time like PKRU.
>>
>> If not, they can continue to be context-switched with the PASID state
>> which does not affect kernel-mode operation.
> PASID?  PASID is all kinds of weird.  I assume you mean switching it
> with all the normal state.

I was grouping PASID along with the CET MSRs because they're the only
supervisor state.  But, yeah, it's all XRSTOR'd at the same spot right
now, user or kernel.