linux-kernel - Re: kvm: RDTSCP on AMD

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Message-ID: <20181210190600.GK4669@habkost.net>
Date:   Mon, 10 Dec 2018 17:06:00 -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.
> 
> > I thought we added documentation mentioning the minimum kernel
> > version required by QEMU, but I can't find it.  In either case,
> > it seems reasonable to require Linux 4.5 or newer on newer
> > machine-types.
> 
> When you say "require" does that mean, one puts it in a text file
> somewhere in the qemu sources or do we enforce it somehow?

I mean documenting it.  We already have code that will print
warnings if a feature isn't available.

See my previous attempt to document the minimum kernel version
at <https://www.mail-archive.com/qemu-devel@nongnu.org/msg486559.html>.

-- 
Eduardo