Re: [PATCH v3 1/2] x86/mce: Reset MCA_SYND between bank scans

[Yazen Ghannam <yazen.ghannam@amd.com>]

On Mon, Sep 21, 2026 at 01:37:02PM +0000, OptoCloud wrote:
> From: Eirik Bøe <git@optocloud.no>
> 
> machine_check_poll() and __mc_scan_banks() both reuse a single
> struct mce_hw_err while iterating over the MCA banks. The record is
> zeroed once before the loop. Each iteration then resets only MISC
> and ADDR.
> 
> On SMCA, mce_read_aux() writes SYND only when MCI_STATUS_SYNDV is
> set. Nothing clears it again, so a bank that does not set SYNDV
> inherits the SYND value read for the previous bank in the same
> scan, and that stale value is printed and handed to the decoders as
> if it belonged to the current error.
> 
> Decoders are expected to ignore MCA_SYND when SYNDV is clear, so
> the stale value is cosmetic.
> 
> Reset SYND at the start of each iteration in both loops, alongside
> the existing MISC and ADDR resets.
> 
> Found by code inspection; not reproduced on hardware.
> 
> Fixes: db819d60f672 ("x86/mce: Add support for new MCA_SYND register")
> Signed-off-by: Eirik Bøe <git@optocloud.no>
> Reviewed-by: Yazen Ghannam <yazen.ghannam@amd.com>
> ---
> 
> Notes (amlog):
>     No v2 of this patch was sent. The numbering follows the series.
>     
>     Changes since v1:
>     - Dropped Cc: stable (Yazen)
>     - Picked up Yazen's Reviewed-by
> 
>  arch/x86/kernel/cpu/mce/core.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
> index ab469605fc89..16183fa4ddc7 100644
> --- a/arch/x86/kernel/cpu/mce/core.c
> +++ b/arch/x86/kernel/cpu/mce/core.c
> @@ -808,6 +808,7 @@ void machine_check_poll(enum mcp_flags flags, mce_banks_t *b)
>  
>  		m->misc = 0;
>  		m->addr = 0;
> +		m->synd = 0;
>  		m->bank = i;
>  
>  		barrier();
> @@ -1347,6 +1348,7 @@ __mc_scan_banks(struct mce_hw_err *err, struct pt_regs *regs,
>  
>  		m->misc = 0;
>  		m->addr = 0;
> +		m->synd = 0;
>  		m->bank = i;
>  
>  		m->status = mce_rdmsrq(mca_msr_reg(i, MCA_STATUS));
> -- 

Hi Eirik,

This patch can be dropped. It isn't necessary with the update to patch
2.

Also, please adjust your email settings to keep all patches within a
revision as a single email thread.

Thanks,
Yazen