The following commit has been merged into the x86/mm branch of tip: Commit-ID: 7a27ef5e83089090f3a4073a9157c862ef00acfc Gitweb: https://git.kernel.org/tip/7a27ef5e83089090f3a4073a9157c862ef00acfc Author: Joerg Roedel <jroedel@xxxxxxx> AuthorDate: Fri, 14 Aug 2020 17:19:47 +02:00 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitterDate: Sat, 15 Aug 2020 13:56:16 +02:00 x86/mm/64: Update comment in preallocate_vmalloc_pages() 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@xxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Link: https://lore.kernel.org/r/20200814151947.26229-3-joro@xxxxxxxxxx --- arch/x86/mm/init_64.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c index 777d835..b5a3fa4 100644 --- a/arch/x86/mm/init_64.c +++ b/arch/x86/mm/init_64.c @@ -1252,14 +1252,19 @@ static void __init preallocate_vmalloc_pages(void) if (!p4d) 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()) 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"; pud = pud_alloc(&init_mm, p4d, addr); if (!pud)
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