linux-kernel - Re: [PATCH v4 05/15] x86/sev: Use kernel provided SVSM Calling Areas

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Date: Mon, 6 May 2024 08:14:34 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Borislav Petkov <bp@...en8.de>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, linux-coco@...ts.linux.dev,
 svsm-devel@...onut-svsm.dev, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>,
 Dan Williams <dan.j.williams@...el.com>, Michael Roth
 <michael.roth@....com>, Ashish Kalra <ashish.kalra@....com>
Subject: Re: [PATCH v4 05/15] x86/sev: Use kernel provided SVSM Calling Areas

On 5/6/24 05:09, Borislav Petkov wrote:
> Ok,
> 
> I think this is very readable and clear what's going on:

I'll test it out.

> 
> static __always_inline void issue_svsm_call(struct svsm_call *call, u8 *pending)
> {
>          register unsigned long rax asm("rax") = call->rax;
>          register unsigned long rcx asm("rcx") = call->rcx;
>          register unsigned long rdx asm("rdx") = call->rdx;
>          register unsigned long r8  asm("r8")  = call->r8;
>          register unsigned long r9  asm("r9")  = call->r9;
> 
>          call->caa->call_pending = 1;
> 
>          asm volatile("rep; vmmcall\n\t"
>                       : "+r" (rax), "+r" (rcx), "+r" (rdx), "+r" (r8), "+r" (r9));
> 
>          xchg(pending, 1);

This isn't quite right. The xchg has to occur between pending and 
call->caa->call_pending.

Thanks,
Tom

> 
>          call->rax_out = rax;
>          call->rcx_out = rcx;
>          call->rdx_out = rdx;
>          call->r8_out = r8;
>          call->r9_out = r9;
> }
> 
> and the asm looks ok but the devil's in the detail.
>