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Re: [Xen-devel] [PATCH] libx86: Elide more empty CPUID leaves when serialising a policy
- To: Jan Beulich <JBeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 23 May 2019 11:38:27 +0100
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- Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
- Delivery-date: Thu, 23 May 2019 10:38:42 +0000
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On 23/05/2019 09:33, Jan Beulich wrote:
>>>> On 22.05.19 at 17:50, <andrew.cooper3@xxxxxxxxxx> wrote:
>> x86_cpuid_copy_to_buffer() currently serialises the full content of the
>> various subleaf unions. While leaves 4, 0xb and 0xd don't have a concrete
>> max_subleaf field, they do have well defined upper bounds.
>>
>> Diffing the results of `xen-cpuid -p` shows the resutling saving:
>>
>> @@ -1,5 +1,5 @@
>> Xen reports there are maximum 114 leaves and 1 MSRs
>> -Raw policy: 93 leaves, 1 MSRs
>> +Raw policy: 38 leaves, 1 MSRs
>> CPUID:
>> leaf subleaf -> eax ebx ecx edx
>> 00000000:ffffffff -> 00000016:756e6547:6c65746e:49656e69
>> @@ -32,7 +32,7 @@ Raw policy: 93 leaves, 1 MSRs
>> MSRs:
>> index -> value
>> 000000ce -> 0000000080000000
>> -Host policy: 93 leaves, 1 MSRs
>> +Host policy: 33 leaves, 1 MSRs
>> CPUID:
>> leaf subleaf -> eax ebx ecx edx
>> 00000000:ffffffff -> 0000000d:756e6547:6c65746e:49656e69
>>
>> which is mostly due to no longer writing out 64 leaves for xstate when (on
>> this CoffeeLake system) 8 will do.
>>
>> Extend the unit tests to cover empty and partially filled subleaf unions.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> For the lib/x86/ part
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Thanks.
> For the test harness part
> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
> No idea how else I should represent that I didn't look overly closely
> at the harness additions.
Well - I can state that the additions to the test harness did find bugs.
Overall, I think the content of tools/tests/ is of relatively little
importance in the grand scheme of things. I certainly don't spend as
much time reviewing the test_x86_emulator changes as the changes to
x86_emulate() itself.
~Andrew
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