Re: [Xen-devel] [PATCH] x86: fix comment on super page alignment requirement

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.09.18 at 12:38, <wei.liu2@xxxxxxxxxx> wrote:
> --- a/xen/arch/x86/setup.c
> +++ b/xen/arch/x86/setup.c
> @@ -944,12 +944,13 @@ void __init noreturn __start_xen(unsigned long mbi_p)
>  
>      /*
>       * Iterate backwards over all superpage-aligned RAM regions.
> -     * 
> -     * We require superpage alignment because the boot allocator is not yet
> -     * initialised. Hence we can only map superpages in the address range
> -     * 0 to BOOTSTRAP_DIRECTMAP_END, as this is guaranteed not to require
> +     *
> +     * We require superpage alignment because the boot allocator is
> +     * not yet initialised. Hence we can only map superpages in the
> +     * address range BOOTSTRAP_MAP_BASE to (BOOTSTRAP_MAP_BASE +
> +     * BOOTSTRAP_MAP_LIMIT), as this is guaranteed not to require

The upper bound is not a sum. But there's then also an apparent
disconnect: BOOTSTRAP_MAP_LIMIT !=
(ARRAY_SIZE(l2_identmap) << L2_PAGETABLE_SHIFT) afaict, yet
the latter is what is used for mapping (and what matches the value
of BOOTSTRAP_DIRECTMAP_END in 4.0.4).

Also, since you're touching almost the entire comment anyway,
would you mind moving it down to where it belongs (immediately
ahead of the for())? Over time more and more things got placed
between the two.

Jan



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