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From:   "Luck, Tony" <tony.luck@intel.com>
To:     "chu, jane" <jane.chu@oracle.com>, "bp@alien8.de" <bp@alien8.de>,
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Subject: RE: [PATCH v5] x86/mce: retrieve poison range from hardware
Thread-Topic: [PATCH v5] x86/mce: retrieve poison range from hardware
Thread-Index: AQHYo9wytRYpFg8fm0OMvCzhpbWWKa2aNUGg
Date:   Mon, 1 Aug 2022 15:58:29 +0000
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References: <20220730061757.3441537-1-jane.chu@oracle.com>
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>	struct mce m;
> +	int lsb =3D PAGE_SHIFT;

Some maintainers like to order local declaration lines from longest to shor=
test
=20
> +     /*
> +      * 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 =3D __ffs64(mem_err->physical_addr_mask);
> +             if (lsb =3D=3D 1)
> +                     lsb =3D 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 =3D __ffs64(mem_err->physical_addr_mask);
                if (lsb =3D=3D 1)
                        lsb =3D PAGE_SHIFT;
        }

-Tony

=09