linux-kernel - Re: [PATCH 1/5] x86/boot/compressed/64: Introduce sev

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Date:   Mon, 19 Oct 2020 17:59:25 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     x86@...nel.org, Joerg Roedel <jroedel@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Martin Radev <martin.b.radev@...il.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] x86/boot/compressed/64: Introduce sev_status

On Mon, Oct 19, 2020 at 05:11:17PM +0200, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@...e.de>
> 
> Introduce sev_status and initialize it together with sme_me_mask to have
> an indicator which SEV features are enabled.
> 
> Signed-off-by: Joerg Roedel <jroedel@...e.de>
> ---
>  arch/x86/boot/compressed/mem_encrypt.S | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/boot/compressed/mem_encrypt.S b/arch/x86/boot/compressed/mem_encrypt.S
> index dd07e7b41b11..0effd58f0095 100644
> --- a/arch/x86/boot/compressed/mem_encrypt.S
> +++ b/arch/x86/boot/compressed/mem_encrypt.S
> @@ -71,6 +71,8 @@ SYM_FUNC_END(get_sev_encryption_bit)
>  SYM_FUNC_START(set_sev_encryption_mask)
>  #ifdef CONFIG_AMD_MEM_ENCRYPT
>  	push	%rbp
> +	push	%rax
> +	push	%rcx

There's no need to save/restore RAX and RCX, they are callee save.  This
function is only called from C, so I doubt it's using a custom ABI.

>  	push	%rdx
>  
>  	movq	%rsp, %rbp		/* Save current stack pointer */
> @@ -81,10 +83,19 @@ SYM_FUNC_START(set_sev_encryption_mask)
>  
>  	bts	%rax, sme_me_mask(%rip)	/* Create the encryption mask */
>  
> +	/* Read sev_status */
> +	movl	$MSR_AMD64_SEV, %ecx
> +	rdmsr
> +	shlq	$32, %rdx
> +	orq	%rdx, %rax
> +	movq	%rax, sev_status(%rip)
> +
>  .Lno_sev_mask:
>  	movq	%rbp, %rsp		/* Restore original stack pointer */
>  
>  	pop	%rdx
> +	pop	%rcx
> +	pop	%rax
>  	pop	%rbp
>  #endif
>  
> @@ -96,5 +107,6 @@ SYM_FUNC_END(set_sev_encryption_mask)
>  
>  #ifdef CONFIG_AMD_MEM_ENCRYPT
>  	.balign	8
> -SYM_DATA(sme_me_mask, .quad 0)
> +SYM_DATA(sme_me_mask,		.quad 0)
> +SYM_DATA(sev_status,		.quad 0)
>  #endif
> -- 
> 2.28.0
>