linux-kernel - Re: kvm: RDTSCP on AMD

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Date:   Tue, 11 Dec 2018 16:23:51 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Eduardo Habkost <ehabkost@...hat.com>,
        Daniel P. Berrangé <berrange@...hat.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        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>,
        Eric Blake <eblake@...hat.com>
Subject: Re: kvm: RDTSCP on AMD

On 11/12/18 12:55, Eduardo Habkost wrote:
>>   - Debian Jessie: 4.5
>>   - Debian Stretch: 4.5
>>   - RHEL-7: 3.10
>>   - Ubuntu LTS (Xenial): 4.5
>>   - OpenSUSE Leap 15: 4.12.14
>>
>> So we can't require Linux 4.5 as a minimum version at this time.
> I'd like us to take a step back and consider what exactly
> "support" means here.  QEMU will still work on older kernels if
> we add RDTSCP to the CPU models, but at the same time I would
> like to document that our strict runnability guarantees may not
> be kept if running Linux < 4.5.

Anyway RHEL does have RDTSC support for AMD, and a bunch of other stuff.
 The frankenkernel's KVM is somewhere between 4.5 and 4.10, with a dash
of 4.20 of course. :)

Paolo