linux-kernel - Re: [GIT PULL] x86/cpu for v5.17

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Date:   Mon, 10 Jan 2022 11:32:26 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Borislav Petkov <bp@...e.de>
Cc:     x86-ml <x86@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [GIT PULL] x86/cpu for v5.17

On Mon, Jan 10, 2022 at 10:35 AM Borislav Petkov <bp@...e.de> wrote:
>
> Right, the only point for doing the vendor check I see here is, well,
> because it is Intel who doesn't have CSTAR, let's check for Intel. But
> yeah, we do avoid the vendor checks if it can be helped.
>
> We can do a synthetic X86_FEATURE flag but that would be a waste. So the
> _safe thing and keep the comment sounds optimal to me.

I agree that a new feature flag for just this would seem a bit
wasteful, and just using wrmsrl_safe() would seem to be the natural
thing to do.

Particularly since that's literally what the wrmsrl's around that
thing do (ie MSR_IA32_SYSENTER_CS and friends). So that vendor check
really stands out as being the odd man out.

               Linus