RE: [PATCH v2] x86/mce: retrieve poison range from hardware whenever supported

[Dan Williams]

Jane Chu wrote:
> With Commit 7917f9cdb503 ("acpi/nfit: rely on mce->misc to determine
> poison granularity") that changed nfit_handle_mce() callback to report
> badrange according to 1ULL << MCI_MISC_ADDR_LSB(mce->misc), it's been
> discovered that the mce->misc LSB field is 0x1000 bytes, hence injecting
> 2 back-to-back poisons and the driver ends up logging 8 badblocks,
> because 0x1000 bytes is 8 512-byte.
> 
> Dan Williams noticed that apei_mce_report_mem_error() hardcode
> the LSB field to PAGE_SHIFT instead of consulting the input
> struct cper_sec_mem_err record.  So change to rely on hardware whenever
> support is available.
> 
> v1: https://lkml.org/lkml/2022/7/15/1040

This should be "Link:" and it should reference lore.kernel.org by
msg-id. Lore is maintained by LF infrastructure and the message-id can
be used to search lore.kernel.org mirrors even if the LF infra is down.

Link: https://lore.kernel.org/r/7ed50fd8-521e-cade-77b1-738b8bfb8502@xxxxxxxxxx

> Signed-off-by: Jane Chu <jane.chu@xxxxxxxxxx>
> ---
>  arch/x86/kernel/cpu/mce/apei.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/mce/apei.c b/arch/x86/kernel/cpu/mce/apei.c
> index 717192915f28..a4d5893632e0 100644
> --- a/arch/x86/kernel/cpu/mce/apei.c
> +++ b/arch/x86/kernel/cpu/mce/apei.c
> @@ -29,6 +29,7 @@
>  void apei_mce_report_mem_error(int severity, struct cper_sec_mem_err *mem_err)
>  {
>  	struct mce m;
> +	int lsb;
>  
>  	if (!(mem_err->validation_bits & CPER_MEM_VALID_PA))
>  		return;
> @@ -37,7 +38,10 @@ void apei_mce_report_mem_error(int severity, struct cper_sec_mem_err *mem_err)
>  	m.bank = -1;
>  	/* Fake a memory read error with unknown channel */
>  	m.status = MCI_STATUS_VAL | MCI_STATUS_EN | MCI_STATUS_ADDRV | MCI_STATUS_MISCV | 0x9f;
> -	m.misc = (MCI_MISC_ADDR_PHYS << 6) | PAGE_SHIFT;
> +	lsb = __builtin_ffs(mem_err->physical_addr_mask) - 1;

Just use the kernel's __ffs64() which does not require the substraction
fixup, and you can assume that physical_address_mask is non-zero just
like trace_extlog_mem_event() does.

> +	if (lsb <= 0)
> +		lsb = PAGE_SHIFT;

This fixup can then be removed as well.

After the above comments are addressed you can add:

Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>