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xen-devel
Re: [Xen-devel] [PATCH 2/2] hvm: allow pass-through of new CPUID feature
Andre Przywara wrote:
Ian Jackson wrote:
Stefano Stabellini writes ("Re: [Xen-devel] [PATCH 2/2] hvm: allow pass-through of
new CPUID features"):
I think Ian was just looking for a well written explanation of why we
need this now :)
OK, I feel challenged, what about this:
The new CPU features are pure "compute" features (ALU/FPU only), they
don't need any support or awareness from any system level software.
Following the definition of virtualization they should be available to
guests unless explicitly disabled.
The AES feature was introduced at the same time as the PCLMULQDQ
feature, AES is passed through, PCLMULQDQ has obviously been forgotten(?).
The Linux kernel uses both instructions in newer versions for optimized
cryptographic algorithms implementation
(arch/x86/crypto/ghash-clmulni-intel_asm.S)
The current version of the Xen hypervisor would deny this feature to any
PV domains, including Dom0, leaving systems running under Xen with an
inferior cryptographic performance.
This patch allows PV domains to use the feature to get on par with
systems running with other virtualization software.
Seems like I was a bit to eager with my rationale, this patch of course
affects only HVM guests.
Regards,
Andre.
--
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
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