Messages in this thread | | | From | David Hildenbrand <> | Subject | Re: [PATCH] mm/sparse: set SECTION_NID_SHIFT to 6 | Date | Tue, 6 Jul 2021 10:36:36 +0200 |
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> Sounds nice to me, so here's a patch. Could you review this? >
Hi,
sorry for the late reply, I was on vacation. Please send it as a proper stand-alone patch next time, such that it
1. won't get silently ignored by reviewers/maintainers within a thread 2. Can easily get picked up/tested
Some minor comments below.
> Thanks, > Naoya Horiguchi > --- > From a146c9f12ae8985c8985a5861330f7528cd14fe8 Mon Sep 17 00:00:00 2001 > From: Naoya Horiguchi <naoya.horiguchi@nec.com> > Date: Mon, 28 Jun 2021 15:50:37 +0900 > Subject: [PATCH] mm/sparse: set SECTION_NID_SHIFT to 6 > > Hagio-san reported that crash utility can see bit 4 in section_mem_map > (SECTION_TAINT_ZONE_DEVICE) to be set, even if we do not use any > ZONE_DEVICE ilke pmem or HMM. This problem could break crash-related
s/ilke/like/
> toolsets and/or other memory analysis tools. >
I'd rephrase this to "Having SECTION_TAINT_ZONE_DEVICE set for wrong sections forces pfn_to_online_page() through the slow path, but doesn't actually break the kernel. However, it can break crash-related toolsets."
However, I am not sure why it actually breaks crash? crash would have to implement the same slow-path check and would have to double-check the sub-section present map. Then, it should just work like pfn_to_online_page() and not have a real issue. What am I missing?
> The root cause is that SECTION_NID_SHIFT is incorrectly set to 3, > while we use lower 5 bits for SECTION_* flags. So bit 3 and 4 can be > overlapped by sub-field for early NID, and bit 4 is unexpectedly set > on (for example) NUMA node id is 2 or 3. > > To fix it, set SECTION_NID_SHIFT to 6 which is the minimum number of > available bits of section flag field. > > [1]: https://github.com/crash-utility/crash/commit/0b5435e10161345cf713ed447a155a611a1b408b
[1] is never referenced
> > Fixes: 1f90a3477df3 ("mm: teach pfn_to_online_page() about ZONE_DEVICE section collisions") > Cc: stable@vger.kernel.org # v5.12+
^ I am not really convinced that this is a stable fix. It forces something through the slow path, but the kernel itself is not broken, no?
> Reported-by: Kazuhito Hagio <k-hagio-ab@nec.com> > Suggested-by: Dan Williams <dan.j.williams@intel.com> > Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com> > --- > include/linux/mmzone.h | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index fcb535560028..d6aa2a196aeb 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -1357,6 +1357,7 @@ extern size_t mem_section_usage_size(void); > * worst combination is powerpc with 256k pages, > * which results in PFN_SECTION_SHIFT equal 6. > * To sum it up, at least 6 bits are available. > + * SECTION_NID_SHIFT is set to 6 based on this fact.
I'd drop that comment or rephrase to ("once this changes, don't forget to adjust SECTION_NID_SHIFT")
> */ > #define SECTION_MARKED_PRESENT (1UL<<0) > #define SECTION_HAS_MEM_MAP (1UL<<1) > @@ -1365,7 +1366,7 @@ extern size_t mem_section_usage_size(void); > #define SECTION_TAINT_ZONE_DEVICE (1UL<<4) > #define SECTION_MAP_LAST_BIT (1UL<<5) > #define SECTION_MAP_MASK (~(SECTION_MAP_LAST_BIT-1)) > -#define SECTION_NID_SHIFT 3 > +#define SECTION_NID_SHIFT 6 > > static inline struct page *__section_mem_map_addr(struct mem_section *section) > { >
Change itself looks correct to me.
Acked-by: David Hildenbrand <david@redhat.com>
-- Thanks,
David / dhildenb
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