linux-kernel - Re: [RESEND PATCH v5] x86/boot: Don't return encryption mask from __startup

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Message-ID: <87qzz1mb9z.ffs@tglx>
Date: Mon, 30 Jun 2025 18:42:16 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Khalid Ali <khaliidcaliy@...il.com>, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com
Cc: x86@...nel.org, hpa@...or.com, linux-kernel@...r.kernel.org, Khalid Ali
 <khaliidcaliy@...il.com>, Kai Huang <kai.huang@...el.com>
Subject: Re: [RESEND PATCH v5] x86/boot: Don't return encryption mask from
 __startup_64()

Khalid!

On Wed, Jun 25 2025 at 16:02, Khalid Ali wrote:
> From: Khalid Ali <khaliidcaliy@...il.com>
>
> Currently, __startup_64() returns encryption mask to the caller, however
> caller can directly access the encryption.
>
> The C code can access encryption by including
> arch/x86/include/asm/setup.h and calling sme_get_me_mask(). The assembly
> code can access directly via "sme_me_mask" variable.
>
> This patches accounts that, by adjusting __startup_64() to not return

This patch.... I pointed you to the tip tree documentation before ....

> encryption mask, and update startup_64() to access "sme_me_mask" only if
> CONFIG_AMD_MEM_ENCRYPT is set.
>
> This cleans up the function and does seperation of concern.
> __startup_64() should focus on action like encrypting the kernel, and
> let the caller retrieve the mask directly.
>
> CHanges in v5:
>  * Improve commit message for better clarity.
>  * Fix some issues returned by kernel test robot.
>  * Add Huang, Kai Ack tag.

Please put this behind the --- seperator. It's not part of the change
log. That's documented too.

> Signed-off-by: Khalid Ali <khaliidcaliy@...il.com>
> Acked-by: Kai Huang <kai.huang@...el.com>
> ---
>  arch/x86/boot/startup/map_kernel.c | 11 +++--------
>  arch/x86/include/asm/setup.h       |  2 +-
>  arch/x86/kernel/head_64.S          |  8 +++-----
>  3 files changed, 7 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/boot/startup/map_kernel.c b/arch/x86/boot/startup/map_kernel.c
> index 332dbe6688c4..0425d49be16e 100644
> --- a/arch/x86/boot/startup/map_kernel.c
> +++ b/arch/x86/boot/startup/map_kernel.c
> @@ -30,7 +30,7 @@ static inline bool check_la57_support(void)
>  	return true;
>  }
>  
> -static unsigned long __head sme_postprocess_startup(struct boot_params *bp,
> +static void __head sme_postprocess_startup(struct boot_params *bp,
>  						    pmdval_t *pmd,
>  						    unsigned long p2v_offset)

See documentation about parameter alignment.

>  {
> @@ -68,11 +68,6 @@ static unsigned long __head sme_postprocess_startup(struct boot_params *bp,
>  		}
>  	}
>  
> -	/*
> -	 * Return the SME encryption mask (if SME is active) to be used as a
> -	 * modifier for the initial pgdir entry programmed into CR3.
> -	 */
> -	return sme_get_me_mask();
>  }
>  
>  /*
> @@ -84,7 +79,7 @@ static unsigned long __head sme_postprocess_startup(struct boot_params *bp,
>   * the 1:1 mapping of memory. Kernel virtual addresses can be determined by
>   * subtracting p2v_offset from the RIP-relative address.
>   */
> -unsigned long __head __startup_64(unsigned long p2v_offset,
> +void __head __startup_64(unsigned long p2v_offset,
>  				  struct boot_params *bp)

Ditto

>  	/*
>  	 * Perform pagetable fixups. Additionally, if SME is active, encrypt
> -	 * the kernel and retrieve the modifier (SME encryption mask if SME
> -	 * is active) to be added to the initial pgdir entry that will be
> -	 * programmed into CR3.
> +	 * the kernel.

Why are you dropping valuable information from that comment, instead of
moving the important information about the SME mask next to the code
which retrieves it?

Thanks,

        tglx