From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH] x86emul: support clzero
Date: Thu, 24 Sep 2015 12:59:01 +0100
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To: Jan Beulich <JBeulich@suse.com>
Cc: xen-devel <xen-devel@lists.xenproject.org>, Keir Fraser <keir@xen.org>, Aravind Gopalakrishnan <aravind.gopalakrishnan@amd.com>, suravee.suthikulpanit@amd.com
List-Id: xen-devel@lists.xenproject.org

On 24/09/15 09:02, Jan Beulich wrote:
>>>> On 23.09.15 at 19:37, <andrew.cooper3@citrix.com> wrote:
>> On 22/09/15 14:06, Jan Beulich wrote:
>>> ... in anticipation of this possibly going to get used by guests for
>>> basic thinks like memset() or clearing or pages.
>>>
>>> Since the emulation doesn't use clzero itself, checking the guest's
>>> CPUID for the feature to be exposed is (intentionally) being avoided
>>> here. All that's required is sensible guest side data for the clflush
>>> line size.
>>>
>>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>> Where have you found this instruction?  Googling, I have found a
>> presentation talking about it being new in the new AMD Zen cores, but I
>> still can't locate any technical documentation on the matter.
> Sadly no technical documentation so far, despite me pinging for it
> after the respective binutils patch
> (https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commitdiff;h=029f3522619e8b77a7b848be23f4c13e50087d8b)
> got posted and went in.

While I don't see an obvious issue with your patch, I can't claim to
have reviewed it without some documentation to refer to.

Aravind/Suravee: Any ideas when the AMD manuals might be updated to
include this?

~Andrew