linux-kernel - Re: [PATCH 1/6] x86/tdx: Support hypercalls for TDX guests on Hyper-V

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Date:   Wed, 23 Nov 2022 08:04:44 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Dexuan Cui <decui@...rosoft.com>,
        "'ak@...ux.intel.com'" <ak@...ux.intel.com>,
        "'arnd@...db.de'" <arnd@...db.de>, "'bp@...en8.de'" <bp@...en8.de>,
        "'brijesh.singh@....com'" <brijesh.singh@....com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "'dave.hansen@...ux.intel.com'" <dave.hansen@...ux.intel.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "'hpa@...or.com'" <hpa@...or.com>,
        "'jane.chu@...cle.com'" <jane.chu@...cle.com>,
        "'kirill.shutemov@...ux.intel.com'" <kirill.shutemov@...ux.intel.com>,
        KY Srinivasan <kys@...rosoft.com>,
        "'linux-arch@...r.kernel.org'" <linux-arch@...r.kernel.org>,
        "'linux-hyperv@...r.kernel.org'" <linux-hyperv@...r.kernel.org>,
        "'luto@...nel.org'" <luto@...nel.org>,
        "'mingo@...hat.com'" <mingo@...hat.com>,
        "'peterz@...radead.org'" <peterz@...radead.org>,
        "'rostedt@...dmis.org'" <rostedt@...dmis.org>,
        "'sathyanarayanan.kuppuswamy@...ux.intel.com'" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "'seanjc@...gle.com'" <seanjc@...gle.com>,
        "'tglx@...utronix.de'" <tglx@...utronix.de>,
        "'tony.luck@...el.com'" <tony.luck@...el.com>,
        "'wei.liu@...nel.org'" <wei.liu@...nel.org>,
        "'x86@...nel.org'" <x86@...nel.org>
Cc:     "'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/6] x86/tdx: Support hypercalls for TDX guests on Hyper-V

On 11/22/22 17:56, Dexuan Cui wrote:
>> From: Dexuan Cui
>> [...]
>> The existing asm code for __tdx_hypercall() passes through R10~R15
>> (see TDVMCALL_EXPOSE_REGS_MASK) to the (KVM) hypervisor.
>>
>> Unluckily, for Hyper-V, we need to pass through RDX, R8, R10 and R11
>> to Hyper-V, so I don't think I can use the existing __tdx_hypercall() ?
> I'm checking with the Hyper-V team to see if it's possible for them
> to not use RDX and R8, and use R12 and R13 instead. Will keep the
> thread updated.

That would be nice.  But, to be honest, I don't expect them to change
the ABI for one OS.  It's not a big deal to just make the function a bit
more flexible.