Re: [PATCH] x86emul: support clzero

[Andrew Cooper <andrew.cooper3@citrix.com>]

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