linux-kernel - RE: [PATCH v5] x86/mce: retrieve poison range from hardware

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Date:   Mon, 1 Aug 2022 15:58:29 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     "chu, jane" <jane.chu@...cle.com>, "bp@...en8.de" <bp@...en8.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "hch@....de" <hch@....de>,
        "nvdimm@...ts.linux.dev" <nvdimm@...ts.linux.dev>
Subject: RE: [PATCH v5] x86/mce: retrieve poison range from hardware

>	struct mce m;
> +	int lsb = PAGE_SHIFT;

Some maintainers like to order local declaration lines from longest to shortest
 
> +     /*
> +      * 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) {
> +             lsb = __ffs64(mem_err->physical_addr_mask);
> +             if (lsb == 1)
> +                     lsb = PAGE_SHIFT;
> +     }


The comment above __ffs64() says:

* The result is not defined if no bits are set, so check that @word
 * is non-zero before calling this.

So if the intent is "extra safe" should check for that:

        if (mem_err->validation_bits & CPER_MEM_VALID_PA_MASK &&
            mem_err->physical_addr_mask) {
                lsb = __ffs64(mem_err->physical_addr_mask);
                if (lsb == 1)
                        lsb = PAGE_SHIFT;
        }

-Tony