Re: [PATCH 2/3] x86/mce/amd: Reset MCA_SYND1/2 between bank scans

[Yazen Ghannam]

On Sun, Aug 30, 2026 at 04:42:54AM +0000, OptoCloud wrote:
> Same issue as the MCA_SYND leak, for the two supplemental AMD
> syndrome registers. mce_read_aux() writes
> err->vendor.amd.synd1/synd2 only when MCI_STATUS_SYNDV is set, and
> nothing clears them between bank iterations in either
> machine_check_poll() or __mc_scan_banks(). A bank without SYNDV can
> inherit synd1/synd2 from an earlier bank in the same scan.
> 
> Reset both fields at the start of each iteration in both loops.
> 
> Found by code inspection; not reproduced on hardware.
> 
> Fixes: d4fca1358ea9 ("x86/MCE/AMD: Add support for new MCA_SYND{1,2} registers")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Eirik Bøe <git@xxxxxxxxxxxx>

The same feedback from patch 1 applies.

> ---
>  arch/x86/kernel/cpu/mce/core.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
> index 16183fa4ddc7..e4e588d02a18 100644
> --- a/arch/x86/kernel/cpu/mce/core.c
> +++ b/arch/x86/kernel/cpu/mce/core.c
> @@ -809,6 +809,8 @@ void machine_check_poll(enum mcp_flags flags, mce_banks_t *b)
>  		m->misc = 0;
>  		m->addr = 0;
>  		m->synd = 0;
> +		err.vendor.amd.synd1 = 0;
> +		err.vendor.amd.synd2 = 0;
>  		m->bank = i;
>  
>  		barrier();
> @@ -1349,6 +1351,8 @@ __mc_scan_banks(struct mce_hw_err *err, struct pt_regs *regs,
>  		m->misc = 0;
>  		m->addr = 0;
>  		m->synd = 0;
> +		err->vendor.amd.synd1 = 0;
> +		err->vendor.amd.synd2 = 0;
>  		m->bank = i;
>  
>  		m->status = mce_rdmsrq(mca_msr_reg(i, MCA_STATUS));
> -- 

At this point, maybe we should consider having a "reset fields" helper
function?

Thanks,
Yazen