Le 16/04/2021 à 11:28, Steven Price a écrit :
On 15/04/2021 18:18, Christophe Leroy wrote:
In order to support large pages on powerpc, notepage()
needs to know the page size of the page.
Add a page_size argument to notepage().
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
---
arch/arm64/mm/ptdump.c | 2 +-
arch/riscv/mm/ptdump.c | 2 +-
arch/s390/mm/dump_pagetables.c | 3 ++-
arch/x86/mm/dump_pagetables.c | 2 +-
include/linux/ptdump.h | 2 +-
mm/ptdump.c | 16 ++++++++--------
6 files changed, 14 insertions(+), 13 deletions(-)
[...]
diff --git a/mm/ptdump.c b/mm/ptdump.c
index da751448d0e4..61cd16afb1c8 100644
--- a/mm/ptdump.c
+++ b/mm/ptdump.c
@@ -17,7 +17,7 @@ static inline int note_kasan_page_table(struct mm_walk *walk,
{
struct ptdump_state *st = walk->private;
- st->note_page(st, addr, 4, pte_val(kasan_early_shadow_pte[0]));
+ st->note_page(st, addr, 4, pte_val(kasan_early_shadow_pte[0]), PAGE_SIZE);
I'm not completely sure what the page_size is going to be used for, but note that KASAN presents an
interesting case here. We short-cut by detecting it's a KASAN region at a high level
(PGD/P4D/PUD/PMD) and instead of walking the tree down just call note_page() *once* but with
level==4 because we know KASAN sets up the page table like that.
However the one call actually covers a much larger region - so while PAGE_SIZE matches the level it
doesn't match the region covered. AFAICT this will lead to odd results if you enable KASAN on powerpc.
Hum .... I successfully tested it with KASAN, I now realise that I tested it with
CONFIG_KASAN_VMALLOC selected. In this situation, since
https://github.com/torvalds/linux/commit/af3d0a686 we don't have any common shadow page table anymore.
I'll test again without CONFIG_KASAN_VMALLOC.
To be honest I don't fully understand why powerpc requires the page_size - it appears to be using it
purely to find "holes" in the calls to note_page(), but I haven't worked out why such holes would
occur.
I was indeed introduced for KASAN. We have a first commit
https://github.com/torvalds/linux/commit/cabe8138 which uses page size to detect whether it is a
KASAN like stuff.
Then came https://github.com/torvalds/linux/commit/b00ff6d8c as a fix. I can't remember what the
problem was exactly, something around the use of hugepages for kernel memory, came as part of the
series
https://patchwork.ozlabs.org/project/linuxppc-dev/cover/cover.1589866984.git.christophe.leroy@xxxxxxxxxx/
Christophe
