linux-kernel - RE: [PATCH 2/9] x86/hyperv: Support hypercalls for fully enlightened TDX guests

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Message-ID: <SA1PR21MB1335A994B0EAD226CF2D15FEBF1CA@SA1PR21MB1335.namprd21.prod.outlook.com>
Date:   Wed, 23 Aug 2023 17:40:15 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     Tianyu Lan <ltykernel@...il.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "arnd@...db.de" <arnd@...db.de>, "bp@...en8.de" <bp@...en8.de>,
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        Haiyang Zhang <haiyangz@...rosoft.com>,
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        KY Srinivasan <kys@...rosoft.com>,
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CC:     "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
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Subject: RE: [PATCH 2/9] x86/hyperv: Support hypercalls for fully enlightened
 TDX guests

> From: Tianyu Lan <ltykernel@...il.com>
> Sent: Wednesday, August 23, 2023 12:06 AM
> To: Dexuan Cui <decui@...rosoft.com>; ak@...ux.intel.com;
> [...]
> On 8/12/2023 6:18 AM, Dexuan Cui wrote:
> > A fully enlightened TDX guest on Hyper-V (i.e. without the paravisor) only
> > uses the GHCI call rather than hv_hypercall_pg.
> >
> > In hv_do_hypercall(), Hyper-V requires that the input/output addresses
> > must have the cc_mask.
I'll remove the above sentence, since this is no longer true on
generally available Hyper-V: cc_mask still works, but it's not required.

> > [...]
> Reviewed-by: Tianyu Lan <tiala@...rosoft.com>
Thanks!

> > --- a/arch/x86/hyperv/hv_init.c
> > +++ b/arch/x86/hyperv/hv_init.c
> > @@ -481,6 +481,10 @@ void __init hyperv_init(void)
> >   	/* Hyper-V requires to write guest os id via ghcb in SNP IVM. */
> >   	hv_ghcb_msr_write(HV_X64_MSR_GUEST_OS_ID, guest_id);
> >
> > +	/* A TDX guest uses the GHCI call rather than hv_hypercall_pg. */
> > +	if (hv_isolation_type_tdx())
> > +		goto skip_hypercall_pg_init;
> > +
> 
> Nitpick:
> 	Put hypercal page initialization code into a sepearate function and
> skip the function in the tdx guest instead of adding the label.
This is doable. The intention here is to minimize the changes.
In the future, we'll introduce a hypercall function structure. We can
do code refactoring at that time.