linux-kernel - Re: [PATCH 03/10] x86/tdx: Move FRAME_BEGIN/END to TDX_MODULE

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Date:   Wed, 12 Jul 2023 15:05:51 -0700
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     Kai Huang <kai.huang@...el.com>
Cc:     peterz@...radead.org, kirill.shutemov@...ux.intel.com,
        linux-kernel@...r.kernel.org, dave.hansen@...el.com,
        tglx@...utronix.de, bp@...en8.de, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, seanjc@...gle.com, pbonzini@...hat.com,
        kvm@...r.kernel.org, isaku.yamahata@...el.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com,
        isaku.yamahata@...il.com
Subject: Re: [PATCH 03/10] x86/tdx: Move FRAME_BEGIN/END to TDX_MODULE_CALL
 asm macro

On Wed, Jul 12, 2023 at 08:55:17PM +1200,
Kai Huang <kai.huang@...el.com> wrote:

> Currently, the TDX_MODULE_CALL asm macro and the __tdx_module_call()
> take registers directly as input and a 'struct tdx_module_output' as
> optional output.  This is different from the __tdx_hypercall(), which
> simply uses a structure to carry all input/output.  There's no point to
> leave __tdx_module_call() complicated as it is.
> 
> As a preparation to simplify the __tdx_module_call() to make it look
> like __tdx_hypercall(), move FRAME_BEGIN/END and RET from the
> __tdx_module_call() to the TDX_MODULE_CALL assembly macro.  This also
> allows more implementation flexibility of the assembly inside the
> TDX_MODULE_CALL macro, e.g., allowing putting an _ASM_EXTABLE() after
> the main body of the assembly.
> 
> This is basically based on Peter's code.
> 
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Kai Huang <kai.huang@...el.com>
> ---
>  arch/x86/coco/tdx/tdcall.S      | 3 ---
>  arch/x86/virt/vmx/tdx/tdxcall.S | 5 +++++
>  2 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/coco/tdx/tdcall.S b/arch/x86/coco/tdx/tdcall.S
> index 2eca5f43734f..e5d4b7d8ecd4 100644
> --- a/arch/x86/coco/tdx/tdcall.S
> +++ b/arch/x86/coco/tdx/tdcall.S
> @@ -78,10 +78,7 @@
>   * Return status of TDCALL via RAX.
>   */
>  SYM_FUNC_START(__tdx_module_call)
> -	FRAME_BEGIN
>  	TDX_MODULE_CALL host=0
> -	FRAME_END
> -	RET
>  SYM_FUNC_END(__tdx_module_call)
>  
>  /*
> diff --git a/arch/x86/virt/vmx/tdx/tdxcall.S b/arch/x86/virt/vmx/tdx/tdxcall.S
> index 3524915d8bd9..b5ab919c7fa8 100644
> --- a/arch/x86/virt/vmx/tdx/tdxcall.S
> +++ b/arch/x86/virt/vmx/tdx/tdxcall.S
> @@ -1,5 +1,6 @@
>  /* SPDX-License-Identifier: GPL-2.0 */
>  #include <asm/asm-offsets.h>
> +#include <asm/frame.h>
>  #include <asm/tdx.h>
>  
>  /*
> @@ -18,6 +19,7 @@
>   *            TDX module.
>   */
>  .macro TDX_MODULE_CALL host:req
> +	FRAME_BEGIN
>  	/*
>  	 * R12 will be used as temporary storage for struct tdx_module_output
>  	 * pointer. Since R12-R15 registers are not used by TDCALL/SEAMCALL
> @@ -91,4 +93,7 @@
>  .Lno_output_struct:
>  	/* Restore the state of R12 register */
>  	pop %r12
> +
> +	FRAME_END
> +	RET
>  .endm
> -- 
> 2.41.0
> 

Reviewed-by: Isaku Yamahata <isaku.yamahata@...el.com>
-- 
Isaku Yamahata <isaku.yamahata@...il.com>