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

[Siddharth Chandrasekaran <sidcha@amazon.de>]

On Thu, Apr 08, 2021 at 04:30:18PM +0000, Wei Liu wrote:
> 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:
> > > On 08/04/21 17:40, Siddharth Chandrasekaran wrote:
> > > > > > > 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?

Yes all of them are from TLFS. We are implementing VSM and there are a
bunch of hypercalls that we have implemented to manage VTL switches,
memory protection and virtual interrupts.

The following 3 hypercalls that use the XMM fast hypercalls are relevant
to this patch set:

HvCallModifyVtlProtectionMask
HvGetVpRegisters 
HvSetVpRegisters 

~ Sid.



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