Le 28/06/2021 à 03:12, Andrew Morton a écrit :
On Fri, 25 Jun 2021 05:10:12 +0000 (UTC) Christophe Leroy <christophe.leroy@xxxxxxxxxx> wrote:
Pagewalk ignores hugepd entries and walk down the tables
as if it was traditionnal entries, leading to crazy result.
Add walk_hugepd_range() and use it to walk hugepage tables.
More details, please? I assume "crazy result" is userspace visible?
For how long has this bug existed? Is a -stable backport needed? Has
a Fixes: commit been identified? etcetera!
I discovered the problem while porting powerpc to generic page table dump.
The generic page table dump uses walk_page_range_novma() .
Yes, "crazy result" is that when dumping /sys/kernel/debug/kernel_page_tables, you get random
entries because at the time being the pagewalk code sees huge page directories as standard page tables.
The bug has always existed as far as I can see, but as no other architectures than powerpc use huge
page directories, it only pops up now when powerpc is trying to use that generic page walking code.
So I don't think it is worth a backport to -stable, and about a Fixes: tag I don't know.
IIUC, hugepd was introduced for the first time in mm by commit cbd34da7dc9a ("mm: move the powerpc
hugepd code to mm/gup.c")
Before that, hugepd was internal to powerpc.
I guess you are asking about Fixes: tag and backporting because of the patch subject.
Should I reword the page subject to something like "mm: enable the generic page walk code to walk
huge page directories" ?
