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

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Message-ID: <20210408174521.GF32315@u366d62d47e3651.ant.amazon.com>
Date:   Thu, 8 Apr 2021 19:45:22 +0200
From:   Siddharth Chandrasekaran <sidcha@...zon.de>
To:     Wei Liu <wei.liu@...nel.org>
CC:     Paolo Bonzini <pbonzini@...hat.com>, <kys@...rosoft.com>,
        <haiyangz@...rosoft.com>, <sthemmin@...rosoft.com>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
        <x86@...nel.org>, <hpa@...or.com>, <seanjc@...gle.com>,
        <vkuznets@...hat.com>, <wanpengli@...cent.com>,
        <jmattson@...gle.com>, <joro@...tes.org>, <graf@...zon.com>,
        <eyakovl@...zon.de>, <linux-hyperv@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>
Subject: Re: [PATCH 0/4] Add support for XMM fast hypercalls

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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