linux-kernel - Re: FSGSBASE seems to be busted on Xen PV

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Message-ID: <87eepss02j.fsf@nanos.tec.linutronix.de>
Date:   Sat, 04 Jul 2020 00:31:00 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andrew Cooper <andrew.cooper3@...rix.com>,
        Andy Lutomirski <luto@...nel.org>,
        xen-devel <xen-devel@...ts.xenproject.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Juergen Gross <jgross@...e.com>,
        Jan Beulich <jbeulich@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     X86 ML <x86@...nel.org>
Subject: Re: FSGSBASE seems to be busted on Xen PV

Andrew Cooper <andrew.cooper3@...rix.com> writes:
> On 03/07/2020 18:10, Andy Lutomirski wrote:
>> If you can't get this fixed in upstream Xen reasonably quickly, we may
>> need to disable FSGSBASE in a Xen PV guest in Linux.
>
> This has come up several times before, but if its actually breaking
> userspace then Xen needs to change.
>
> I'll see about making something which is rather more robust.

You mean disabling XEN PV completely? That would be indeed very robust
and allows us to get rid of lots of obscure code. Feel free to add my
Acked-by :)

Thanks,

        tglx