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Date:   Wed, 27 Jul 2022 11:56:40 -0700
From:   Dan Williams <dan.j.williams@intel.com>
To:     Jane Chu <jane.chu@oracle.com>, <tony.luck@intel.com>,
        <bp@alien8.de>, <tglx@linutronix.de>, <mingo@redhat.com>,
        <dave.hansen@linux.intel.com>, <x86@kernel.org>,
        <linux-edac@vger.kernel.org>, <dan.j.williams@intel.com>,
        <linux-kernel@vger.kernel.org>, <hch@lst.de>,
        <nvdimm@lists.linux.dev>
Subject: RE: [PATCH v4] x86/mce: retrieve poison range from hardware
Message-ID: <62e18a687aac2_2d20792944b@dwillia2-xfh.jf.intel.com.notmuch>
References: <20220727184644.2685405-1-jane.chu@oracle.com>
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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.
> 
> Link: https://lore.kernel.org/r/7ed50fd8-521e-cade-77b1-738b8bfb8502@oracle.com
> 
> Reviewed-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Jane Chu <jane.chu@oracle.com>
> ---
>  arch/x86/kernel/cpu/mce/apei.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/mce/apei.c b/arch/x86/kernel/cpu/mce/apei.c
> index 717192915f28..26d63818b2de 100644
> --- a/arch/x86/kernel/cpu/mce/apei.c
> +++ b/arch/x86/kernel/cpu/mce/apei.c
> @@ -29,15 +29,27 @@
>  void apei_mce_report_mem_error(int severity, struct cper_sec_mem_err *mem_err)
>  {
>  	struct mce m;
> +	int grain = PAGE_SHIFT;
>  
>  	if (!(mem_err->validation_bits & CPER_MEM_VALID_PA))
>  		return;
>  
> +	/*
> +	 * Even if the ->validation_bits are set for address mask,
> +	 * to be extra safe, check and reject an error radius '0',
> +	 * and fallback to the default page size.
> +	 */
> +	if (mem_err->validation_bits & CPER_MEM_VALID_PA_MASK) {
> +		grain = ~mem_err->physical_addr_mask + 1;
> +		if (grain == 1)
> +			grain = PAGE_SHIFT;

Wait, if @grain is the number of bits to mask off the address, shouldn't
this be something like:

    grain = min_not_zero(PAGE_SHIFT, hweight64(~mem_err->physical_addr_mask));

...?