linux-kernel - Re: [PATCH] x86/sev: Fix operator precedence in GHCB_MSR_VMPL_REQ

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Message-ID: <20250511085513.GAaCBl8fIwQb7BpjNv@fat_crate.local>
Date: Sun, 11 May 2025 10:55:13 +0200
From: Borislav Petkov <bp@...en8.de>
To: Seongmanlee <cloudlee1719@...il.com>,
	Tom Lendacky <thomas.lendacky@....com>
Cc: x86@...nel.org, leonardo-leecaprio <augustus92@...st.ac.kr>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/sev: Fix operator precedence in
 GHCB_MSR_VMPL_REQ_LEVEL macro

+ Tom.

On Sun, May 11, 2025 at 01:27:24AM +0900, Seongmanlee wrote:
> From: leonardo-leecaprio <augustus92@...st.ac.kr>
> 
> The GHCB_MSR_VMPL_REQ_LEVEL macro lacked parentheses around the bitmask
> expression, causing the shift operation to bind too early. As a result,
> when switching to VMPL2 from VMPL1 (e.g., GHCB_MSR_VMPL_REQ_LEVEL(1)),
> incorrect values such as 0x000000016 were generated instead of the intended
> 0x100000016.
> 
> This patch fixes the precedence issue by grouping the masked value

Avoid having "This patch" or "This commit" in the commit message. It is
tautologically useless.

Also, do

$ git grep 'This patch' Documentation/process

for more details.

> before applying the shift.
> 

Fixes: 34ff65901735 ("x86/sev: Use kernel provided SVSM Calling Areas")

> Signed-off-by: leonardo-leecaprio <augustus92@...st.ac.kr>

Please use your real name.

> ---
>  arch/x86/include/asm/sev-common.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
> index acb85b934..0020d77a0 100644
> --- a/arch/x86/include/asm/sev-common.h
> +++ b/arch/x86/include/asm/sev-common.h
> @@ -116,7 +116,7 @@ enum psc_op {
>  #define GHCB_MSR_VMPL_REQ		0x016
>  #define GHCB_MSR_VMPL_REQ_LEVEL(v)			\
>  	/* GHCBData[39:32] */				\
> -	(((u64)(v) & GENMASK_ULL(7, 0) << 32) |		\
> +	((((u64)(v) & GENMASK_ULL(7, 0)) << 32) |	\
>  	/* GHCBDdata[11:0] */				\
>  	GHCB_MSR_VMPL_REQ)
>  

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette