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Message-ID: <20230713090110.GC3138667@hirez.programming.kicks-ass.net>
Date: Thu, 13 Jul 2023 11:01:10 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: "Huang, Kai" <kai.huang@...el.com>
Cc: "Hansen, Dave" <dave.hansen@...el.com>,
"Christopherson,, Sean" <seanjc@...gle.com>,
"bp@...en8.de" <bp@...en8.de>, "x86@...nel.org" <x86@...nel.org>,
"hpa@...or.com" <hpa@...or.com>,
"mingo@...hat.com" <mingo@...hat.com>,
"kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"pbonzini@...hat.com" <pbonzini@...hat.com>,
"Yamahata, Isaku" <isaku.yamahata@...el.com>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"sathyanarayanan.kuppuswamy@...ux.intel.com"
<sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: Re: [PATCH 07/10] x86/tdx: Extend TDX_MODULE_CALL to support more
TDCALL/SEAMCALL leafs
On Thu, Jul 13, 2023 at 08:09:33AM +0000, Huang, Kai wrote:
> On Wed, 2023-07-12 at 19:11 +0200, Peter Zijlstra wrote:
> > On Wed, Jul 12, 2023 at 08:55:21PM +1200, Kai Huang wrote:
> > > @@ -65,6 +104,37 @@
> > > .endif
> > >
> > > .if \ret
> > > + .if \saved
> > > + /*
> > > + * Restore the structure from stack to saved the output registers
> > > + *
> > > + * In case of VP.ENTER returns due to TDVMCALL, all registers are
> > > + * valid thus no register can be used as spare to restore the
> > > + * structure from the stack (see "TDH.VP.ENTER Output Operands
> > > + * Definition on TDCALL(TDG.VP.VMCALL) Following a TD Entry").
> > > + * For this case, need to make one register as spare by saving it
> > > + * to the stack and then manually load the structure pointer to
> > > + * the spare register.
> > > + *
> > > + * Note for other TDCALLs/SEAMCALLs there are spare registers
> > > + * thus no need for such hack but just use this for all for now.
> > > + */
> > > + pushq %rax /* save the TDCALL/SEAMCALL return code */
> > > + movq 8(%rsp), %rax /* restore the structure pointer */
> > > + movq %rsi, TDX_MODULE_rsi(%rax) /* save %rsi */
> > > + movq %rax, %rsi /* use %rsi as structure pointer */
> > > + popq %rax /* restore the return code */
> > > + popq %rsi /* pop the structure pointer */
> >
> > Urgghh... At least for the \host case you can simply pop %rsi, no?
> > VP.ENTER returns with 0 there IIRC.
>
> No VP.ENTER doesn't return 0 for RAX. Firstly, VP.ENTER can return for many
No, but it *does* return 0 for: RBX,RSI,RDI,R10-R15.
So for \host you can simply do:
pop %rsi
mov $0, TDX_MODULE_rsi(%rsi)
and call it a day.
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