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Re: [Qemu-devel] [PATCH 1/2] i386: remove the new CPUID 'PCONFIG' from I

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH 1/2] i386: remove the new CPUID 'PCONFIG' from Icelake-Server CPU model
Date: Fri, 21 Dec 2018 07:27:36 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1

On 20/12/18 13:50, Robert Hoo wrote:
> On Thu, 2018-12-20 at 13:38 +0100, Paolo Bonzini wrote:
>> On 20/12/18 01:18, Robert Hoo wrote:
>>> I think the sooner, the better. Take the time window that Icelake
>>> CPU
>>> model has just shipped with QEMU 3.1.0 and is not publicly/widely
>>> used
>>> yet.
>> We should still leave it in the 3.1 machine types.  I've just sent a
>> patch to do the same with MPX.
> I took a look your patch of "Disable MPX support on named CPU models".
> Seems you do the same as I do to PCONFIG. So you agree with my above
> patch?:-)
> I won't object that keep it in 3.1 machine type as you do to MPX.

Sorry Robert, I changed my mind.  If no hypervisor exists that enables
PCONFIG for guests (using the PCONFIG_ENABLE processor control),
effectively no one can ever have used it.  We should disable it in all
machine types and Cc qemu-stable.

In fact, the same is true for INTEL_PT, which is not supported by any
released kernel version and, even is going to be available only with a
module parameter when it will be.

This is not the same as MPX, which did work even though nobody was
probably using it.

So this series is correct and I will follow up with one for INTEL_PT;
however, this begs the question of how the patches are being tested.


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