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Date:   Thu, 27 Jul 2023 19:50:57 +0300
From:   kirill.shutemov@linux.intel.com
To:     Kai Huang <kai.huang@intel.com>
Cc:     peterz@infradead.org, linux-kernel@vger.kernel.org,
        dave.hansen@intel.com, tglx@linutronix.de, bp@alien8.de,
        mingo@redhat.com, hpa@zytor.com, x86@kernel.org, seanjc@google.com,
        pbonzini@redhat.com, isaku.yamahata@intel.com,
        sathyanarayanan.kuppuswamy@linux.intel.com,
        n.borisov.lkml@gmail.com
Subject: Re: [PATCH v3 06/12] x86/tdx: Extend TDX_MODULE_CALL to support more
 TDCALL/SEAMCALL leafs
Message-ID: <20230727165057.rdn4txmzdh4yorw5@box.shutemov.name>
References: <cover.1690369495.git.kai.huang@intel.com>
 <3d91bb67e17270d6df6c09308861961e04c13921.1690369495.git.kai.huang@intel.com>
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On Wed, Jul 26, 2023 at 11:25:08PM +1200, Kai Huang wrote:
> @@ -64,6 +103,37 @@
>  .endif
>  
>  .if \ret
> +.if \saved
> +	/*
> +	 * Restore the structure from stack to save 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.
> +	 */
> +	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 */

This looks redundant. You get struct in RSI with popq two lines below.

And please use upper case for registers: RSI instead of %rsi.

> +	popq	%rax		/* restore the return code */
> +	popq	%rsi		/* pop the structure pointer */
> +
> +	/* Copy additional output regs to the structure  */
> +	movq %r12, TDX_MODULE_r12(%rsi)
> +	movq %r13, TDX_MODULE_r13(%rsi)
> +	movq %r14, TDX_MODULE_r14(%rsi)
> +	movq %r15, TDX_MODULE_r15(%rsi)
> +	movq %rbx, TDX_MODULE_rbx(%rsi)
> +	movq %rdi, TDX_MODULE_rdi(%rsi)
> +.endif	/* \saved */
> +
>  	/* Copy output registers to the structure */
>  	movq %rcx, TDX_MODULE_rcx(%rsi)
>  	movq %rdx, TDX_MODULE_rdx(%rsi)

Otherwise, looks sane:

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov