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x86/mm/64: Update comment in preallocate_vmalloc_pages()

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The comment explaining why 4-level systems only need to allocate on
the P4D level caused some confustion. Update it to better explain why
on 4-level systems the allocation on PUD level is necessary.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200814151947.26229-3-joro@8bytes.org
This commit is contained in:
Joerg Roedel 2020-08-14 17:19:47 +02:00 committed by Ingo Molnar
parent 58a18fe95e
commit 7a27ef5e83
1 changed files with 10 additions and 5 deletions
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15
arch/x86/mm/init_64.c
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@ -1252,14 +1252,19 @@ static void __init preallocate_vmalloc_pages(void)
if (!p4d) if (!p4d)
goto failed; goto failed;
/*
* With 5-level paging the P4D level is not folded. So the PGDs
* are now populated and there is no need to walk down to the
* PUD level.
*/
if (pgtable_l5_enabled()) if (pgtable_l5_enabled())
continue; continue;
/*
* The goal here is to allocate all possibly required
* hardware page tables pointed to by the top hardware
* level.
*
* On 4-level systems, the P4D layer is folded away and
* the above code does no preallocation. Below, go down
* to the pud _software_ level to ensure the second
* hardware level is allocated on 4-level systems too.
*/
lvl = "pud"; lvl = "pud";
pud = pud_alloc(&init_mm, p4d, addr); pud = pud_alloc(&init_mm, p4d, addr);
if (!pud) if (!pud)