linux-kernel - Re: kvm: RDTSCP on AMD

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Message-ID: <20181210194725.GM4669@habkost.net>
Date:   Mon, 10 Dec 2018 17:47:25 -0200
From:   Eduardo Habkost <ehabkost@...hat.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Jörg Rödel <joro@...tes.org>,
        Andre Przywara <andre.przywara@....com>,
        kvm ML <kvm@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: kvm: RDTSCP on AMD

On Mon, Dec 10, 2018 at 07:41:53PM +0100, Borislav Petkov wrote:
> On Mon, Dec 10, 2018 at 04:37:30PM -0200, Eduardo Habkost wrote:
> > It isn't as simply as reverting commit 33b5e8c03ae7, but we can
> > surely re-add RDTSCP on pc-*-4.0 and newer.
> 
> Sure. If you could only point me to an example how to add that to
> pc-*-4.0 and newer, I'll gladly cook up a patch and test it.

Sorry, I forgot to reply to this part.

See commit 33b5e8c03ae7 for reference.  The differences will be:
* Instead of removing RDTSCP from builtin_x86_defs, you'll be adding it.
* Instead of adding rdtscp=on entries to PC_COMPAT_2_4, you'll
  be adding rdtscp=off entries to PC_COMPAT_3_1.

PC_COMPAT_3_1 is added by the patch that creates the 4.0
machine-types.  You can find it on my machine-next branch at:

  http://github.com/ehabkost/qemu

-- 
Eduardo