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Subject: Re: [PATCH 0/4] Add support for XMM fast hypercalls
Date:   Thu, 8 Apr 2021 17:40:07 +0200
From:   Siddharth Chandrasekaran <sidcha@amazon.de>
To:     Paolo Bonzini <pbonzini@redhat.com>
CC:     Wei Liu <wei.liu@kernel.org>, <kys@microsoft.com>,
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        <eyakovl@amazon.de>, <linux-hyperv@vger.kernel.org>,
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On Thu, Apr 08, 2021 at 05:30:26PM +0200, Paolo Bonzini wrote:
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>
> On 08/04/21 17:28, Wei Liu 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.

~ Sid.


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