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Date: Sat, 12 Feb 2022 00:12:09 +0000 From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com> To: "Shankar, Ravi V" <ravi.v.shankar@...el.com>, "bsingharora@...il.com" <bsingharora@...il.com>, "hpa@...or.com" <hpa@...or.com>, "Syromiatnikov, Eugene" <esyr@...hat.com>, "peterz@...radead.org" <peterz@...radead.org>, "rdunlap@...radead.org" <rdunlap@...radead.org>, "keescook@...omium.org" <keescook@...omium.org>, "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>, "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>, "Eranian, Stephane" <eranian@...gle.com>, "linux-mm@...ck.org" <linux-mm@...ck.org>, "fweimer@...hat.com" <fweimer@...hat.com>, "nadav.amit@...il.com" <nadav.amit@...il.com>, "jannh@...gle.com" <jannh@...gle.com>, "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>, "kcc@...gle.com" <kcc@...gle.com>, "bp@...en8.de" <bp@...en8.de>, "oleg@...hat.com" <oleg@...hat.com>, "hjl.tools@...il.com" <hjl.tools@...il.com>, "Yang, Weijiang" <weijiang.yang@...el.com>, "Lutomirski, Andy" <luto@...nel.org>, "pavel@....cz" <pavel@....cz>, "arnd@...db.de" <arnd@...db.de>, "Moreira, Joao" <joao.moreira@...el.com>, "tglx@...utronix.de" <tglx@...utronix.de>, "mike.kravetz@...cle.com" <mike.kravetz@...cle.com>, "x86@...nel.org" <x86@...nel.org>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, "Dave.Martin@....com" <Dave.Martin@....com>, "john.allen@....com" <john.allen@....com>, "mingo@...hat.com" <mingo@...hat.com>, "Hansen, Dave" <dave.hansen@...el.com>, "corbet@....net" <corbet@....net>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>, "gorcunov@...il.com" <gorcunov@...il.com> CC: "Yu, Yu-cheng" <yu-cheng.yu@...el.com> Subject: Re: [PATCH 25/35] x86/cet/shstk: Add user-mode shadow stack support On Fri, 2022-02-11 at 15:37 -0800, 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. > > Either way, it would be nice to have some changelog material to that > effect. The only special shadow stack thing the kernel does is WRUSS, which per the SDM only needs the CR4 bit set to work (unlike WRSS). So I think the lazy restore is ok.
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