linux-kernel - Re: [PATCH v5 03/20] x86/mce/amd: Remove smca_banks

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Message-ID: <20250825195403.GA300213@yaz-khff2.amd.com>
Date: Mon, 25 Aug 2025 15:54:03 -0400
From: Yazen Ghannam <yazen.ghannam@....com>
To: Borislav Petkov <bp@...en8.de>
Cc: x86@...nel.org, Tony Luck <tony.luck@...el.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	linux-kernel@...r.kernel.org, linux-edac@...r.kernel.org,
	Smita.KoralahalliChannabasappa@....com,
	Qiuxu Zhuo <qiuxu.zhuo@...el.com>,
	Nikolay Borisov <nik.borisov@...e.com>, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v5 03/20] x86/mce/amd: Remove smca_banks_map

On Mon, Aug 25, 2025 at 08:19:38PM +0200, Borislav Petkov wrote:
> On Mon, Aug 25, 2025 at 05:33:00PM +0000, Yazen Ghannam wrote:
> > The MCx_MISC0[BlkPtr] field was used on legacy systems to hold a
> > register offset for the next MCx_MISC* register. In this way, an
> > implementation-specific number of registers can be discovered at
> > runtime.
> > 
> > The MCAX/SMCA register space simplifies this by always including
> > the MCx_MISC[1-4] registers. The MCx_MISC0[BlkPtr] field is used to
> > indicate (true/false) whether any MCx_MISC[1-4] registers are present.
> > 
> > Currently, MCx_MISC0[BlkPtr] is checked early and cached to be used
> > during sysfs init later. This is unnecessary as the MCx_MISC0 register
> > is read again later anyway.
> > 
> > Remove the smca_banks_map variable as it is effectively redundant, and
> > use a direct register/bit check instead.
> > 
> > Reviewed-by: Qiuxu Zhuo <qiuxu.zhuo@...el.com>
> > Tested-by: Tony Luck <tony.luck@...el.com>
> > Reviewed-by: Tony Luck <tony.luck@...el.com>
> > Signed-off-by: Yazen Ghannam <yazen.ghannam@....com>
> > ---
> > 
> > Notes:
> >     Link:
> >     https://lore.kernel.org/r/20250624-wip-mca-updates-v4-7-236dd74f645f@amd.com
> >     
> >     v4->v5:
> >     * Keep MCx_MISC0[BlkPtr] check to be compliant with uarch.
> 
> I'm not sure I understand what that means...?

I completely removed the check below in previous revisions. But I put
it back to make sure we follow the microarchitecture guidelines, i.e.
the procedure(s) in documentation (APM, PPR, etc.).

	if (!(low & MASK_BLKPTR_LO))
		return 0;

> 
> Anyway, some more cleanup ontop:
> 
> ---
> diff --git a/arch/x86/kernel/cpu/mce/amd.c b/arch/x86/kernel/cpu/mce/amd.c
> index 580682af432d..7e36bc0d0e6c 100644
> --- a/arch/x86/kernel/cpu/mce/amd.c
> +++ b/arch/x86/kernel/cpu/mce/amd.c
> @@ -498,17 +498,6 @@ static void deferred_error_interrupt_enable(struct cpuinfo_x86 *c)
>  	wrmsr(MSR_CU_DEF_ERR, low, high);
>  }
>  
> -static u32 smca_get_block_address(unsigned int bank, unsigned int block, u32 low)
> -{
> -	if (!block)
> -		return MSR_AMD64_SMCA_MCx_MISC(bank);
> -
> -	if (!(low & MASK_BLKPTR_LO))
> -		return 0;
> -
> -	return MSR_AMD64_SMCA_MCx_MISCy(bank, block - 1);
> -}
> -
>  static u32 get_block_address(u32 current_addr, u32 low, u32 high,
>  			     unsigned int bank, unsigned int block,
>  			     unsigned int cpu)
> @@ -518,8 +507,15 @@ static u32 get_block_address(u32 current_addr, u32 low, u32 high,
>  	if ((bank >= per_cpu(mce_num_banks, cpu)) || (block >= NR_BLOCKS))
>  		return addr;
>  
> -	if (mce_flags.smca)
> -		return smca_get_block_address(bank, block, low);
> +	if (mce_flags.smca) {
> +		if (!block)
> +			return MSR_AMD64_SMCA_MCx_MISC(bank);
> +
> +		if (!(low & MASK_BLKPTR_LO))
> +			return 0;
> +
> +		return MSR_AMD64_SMCA_MCx_MISCy(bank, block - 1);
> +	}
>  
>  	/* Fall back to method we used for older processors: */
>  	switch (block) {
> 
> 
> -- 

Looks good to me.

Thanks,
Yazen