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Date:   Fri, 11 Feb 2022 16:07:51 -0800
From:   "Andy Lutomirski" <luto@kernel.org>
To:     "Dave Hansen" <dave.hansen@intel.com>,
        "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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        "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
        linux-doc@vger.kernel.org, linux-mm@kvack.org,
        linux-arch@vger.kernel.org,
        "Linux API" <linux-api@vger.kernel.org>,
        "Arnd Bergmann" <arnd@arndb.de>,
        "Balbir Singh" <bsingharora@gmail.com>,
        "Borislav Petkov" <bp@alien8.de>,
        "Cyrill Gorcunov" <gorcunov@gmail.com>,
        "Dave Hansen" <dave.hansen@linux.intel.com>,
        "Eugene Syromiatnikov" <esyr@redhat.com>,
        "Florian Weimer" <fweimer@redhat.com>,
        "H.J. Lu" <hjl.tools@gmail.com>, "Jann Horn" <jannh@google.com>,
        "Jonathan Corbet" <corbet@lwn.net>,
        "Kees Cook" <keescook@chromium.org>,
        "Mike Kravetz" <mike.kravetz@oracle.com>,
        "Nadav Amit" <nadav.amit@gmail.com>,
        "Oleg Nesterov" <oleg@redhat.com>, "Pavel Machek" <pavel@ucw.cz>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        "Randy Dunlap" <rdunlap@infradead.org>,
        "Shankar, Ravi V" <ravi.v.shankar@intel.com>,
        "Dave Martin" <Dave.Martin@arm.com>,
        "Weijiang Yang" <weijiang.yang@intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        "Moreira, Joao" <joao.moreira@intel.com>,
        "john.allen@amd.com" <john.allen@amd.com>,
        "kcc@google.com" <kcc@google.com>,
        "Eranian, Stephane" <eranian@google.com>
Cc:     "Yu-cheng Yu" <yu-cheng.yu@intel.com>
Subject: Re: [PATCH 25/35] x86/cet/shstk: Add user-mode shadow stack support
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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.

>
> Either way, it would be nice to have some changelog material to that effect.