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SubjectRe: [PATCH 2/3] x86: mtrr_cleanup: first 1M should be coverred in var mtrrs
Yinghai Lu wrote:
> + /*
> + * [0, 1M) should always be coverred by var mtrr with WB
> + * and fixed mtrrs should take effective before var mtrr for it
> + */
> + nr_range = add_range_with_merge(range, nr_range, 0,
> + (1ULL<<(20 - PAGE_SHIFT)) - 1);
> + /* sort the ranges */
> + sort(range, nr_range, sizeof(struct res_range), cmp_range, NULL);
> +

The first 1 MB is a total don't care for the variable MTRRs -- they
don't have to be covered *or* uncovered, since the entire first 1 MB is
addressed by fixed MTRRs.

In practice, it is *likely* that you're going to want to merge it with a
WB MTRR, but with various vendors doing all kinds of strange things on
EFI-damaged platforms, it may not always be that way.

-hpa


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