linux-kernel - Re: [PATCH 00/29] x86: Kernel IBT

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Message-ID: <895e6eb9-39d9-78b3-51c5-95f4eee0cb7a@citrix.com>
Date:   Sat, 19 Feb 2022 16:00:59 +0000
From:   Andrew Cooper <Andrew.Cooper3@...rix.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
CC:     "Poimboe, Josh" <jpoimboe@...hat.com>,
        "hjl.tools@...il.com" <hjl.tools@...il.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "joao@...rdrivepizza.com" <joao@...rdrivepizza.com>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "samitolvanen@...gle.com" <samitolvanen@...gle.com>,
        "ndesaulniers@...gle.com" <ndesaulniers@...gle.com>,
        "Milburn, Alyssa" <alyssa.milburn@...el.com>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>
Subject: Re: [PATCH 00/29] x86: Kernel IBT

On 19/02/2022 09:58, Peter Zijlstra wrote:
> On Sat, Feb 19, 2022 at 01:29:45AM +0000, Edgecombe, Rick P wrote:
>> On Fri, 2022-02-18 at 17:49 +0100, Peter Zijlstra wrote:
>>> This is an (almost!) complete Kernel IBT implementation. It's been
>>> self-hosting
>>> for a few days now. That is, it runs on IBT enabled hardware
>>> (Tigerlake) and is
>>> capable of building the next kernel.
>>>
>>> It is also almost clean on allmodconfig using GCC-11.2.
>>>
>>> The biggest TODO item at this point is Clang, I've not yet looked at
>>> that.
>> Do you need to turn this off before kexec?
> Probably... :-) I've never looked at that code though; so I'm not
> exactly sure where to put things.
>
> I'm assuming kexec does a hot-unplug of all but the boot-cpu which then
> leaves only a single CPU with state in machine_kexec() ? Does the below
> look reasonable?

If you skip writing to S_CET on hardware that doesn't have it, probably.

~Andrew