Re: [PATCH 0/4] Add support for XMM fast hypercalls

On Thu, Apr 08, 2021 at 05:54:43PM +0200, Siddharth Chandrasekaran wrote:

On Thu, Apr 08, 2021 at 05:48:19PM +0200, Paolo Bonzini wrote:

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On 08/04/21 17:40, Siddharth Chandrasekaran wrote:

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Although the Hyper-v TLFS mentions that a guest cannot use this feature
unless the hypervisor advertises support for it, some hypercalls which
we plan on upstreaming in future uses them anyway.

No, please don't do this. Check the feature bit(s) before you issue
hypercalls which rely on the extended interface.

Perhaps Siddharth should clarify this, but I read it as Hyper-V being
buggy and using XMM arguments unconditionally.

The guest is at fault here as it expects Hyper-V to consume arguments
from XMM registers for certain hypercalls (that we are working) even if
we didn't expose the feature via CPUID bits.

What guest is that?

It is a Windows Server 2016.

Can you be more specific? Are you implementing some hypercalls from
TLFS? If so, which ones?

Wei.