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Re: [RFC PATCH 0/7] Support protection keys in an AMD EPYC-Milan VM
From: |
David Edmondson |
Subject: |
Re: [RFC PATCH 0/7] Support protection keys in an AMD EPYC-Milan VM |
Date: |
Mon, 14 Jun 2021 17:21:12 +0100 |
On Friday, 2021-06-11 at 18:01:55 +02, Paolo Bonzini wrote:
> First of all, sorry for the delayed review.
>
> On 20/05/21 16:56, David Edmondson wrote:
>> AMD EPYC-Milan CPUs introduced support for protection keys, previously
>> available only with Intel CPUs.
>>
>> AMD chose to place the XSAVE state component for the protection keys
>> at a different offset in the XSAVE state area than that chosen by
>> Intel.
>>
>> To accommodate this, modify QEMU to behave appropriately on AMD
>> systems, allowing a VM to properly take advantage of the new feature.
>
> Uff, that sucks. :(
>
> If I understand correctly, the problem is that the layout of
> KVM_GET_XSAVE/KVM_SET_XSAVE depends on the host CPUID, which in
> retrospect would be obvious. Is that correct?
Yes.
> If so, it would make sense and might even be easier to drop all usage
> of X86XSaveArea:
>
> * update ext_save_areas based on CPUID information in kvm_cpu_instance_init
>
> * make x86_cpu_xsave_all_areas and x86_cpu_xrstor_all_areas use the
> ext_save_areas offsets to build pointers to XSaveAVX, XSaveBNDREG, etc.
>
> What do you think?
I will produce a patch and send it out.
> Paolo
>
>> Further, avoid manipulating XSAVE state components that are not
>> present on AMD systems.
>>
>> The code in patch 6 that changes the CPUID 0x0d leaf is mostly dumped
>> somewhere that seemed to work - I'm not sure where it really belongs.
>>
>> David Edmondson (7):
>> target/i386: Declare constants for XSAVE offsets
>> target/i386: Use constants for XSAVE offsets
>> target/i386: Clarify the padding requirements of X86XSaveArea
>> target/i386: Prepare for per-vendor X86XSaveArea layout
>> target/i386: Introduce AMD X86XSaveArea sub-union
>> target/i386: Adjust AMD XSAVE PKRU area offset in CPUID leaf 0xd
>> target/i386: Manipulate only AMD XSAVE state on AMD
>>
>> target/i386/cpu.c | 19 +++++----
>> target/i386/cpu.h | 80 ++++++++++++++++++++++++++++--------
>> target/i386/kvm/kvm.c | 57 +++++++++----------------
>> target/i386/tcg/fpu_helper.c | 20 ++++++---
>> target/i386/xsave_helper.c | 70 +++++++++++++++++++------------
>> 5 files changed, 152 insertions(+), 94 deletions(-)
>>
dme.
--
Oliver darling, call Mister Haney, I think our speakers are blown.