linux-kernel - Re: [patch 13/31] x86/fpu: Move KVMs FPU swapping to FPU core

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 14 Oct 2021 16:37:07 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        "Liu, Jing2" <jing2.liu@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     "x86@...nel.org" <x86@...nel.org>,
        "Bae, Chang Seok" <chang.seok.bae@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Nakajima, Jun" <jun.nakajima@...el.com>,
        Jing Liu <jing2.liu@...ux.intel.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "Cooper, Andrew" <andrew.cooper3@...rix.com>
Subject: Re: [patch 13/31] x86/fpu: Move KVMs FPU swapping to FPU core

On Thu, Oct 14 2021 at 16:09, Thomas Gleixner wrote:
> On Thu, Oct 14 2021 at 11:01, Paolo Bonzini wrote:
>
> Also you really should not wait until _all_ dynamic states are cleared
> in guest XFD. Because a guest which has bit 18 and 19 available but only
> uses one of them is going to trap on every other context switch due to
> XFD writes.
>
> So you check for
>
>    (guest_xfd & guest_perm) != guest_perm)
>
> and
>
>    (guest_xr0 & guest_perm) != 0
>
> If both are true, then you reallocate the buffers for _all_ permitted
> states _and_ set XFD to pass through.

And for that to work we must write XFD _before_ XSETBV in the guest boot
phase.

Thanks,

        tglx