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6a288a4ddb
__GFP_ZEROTAGS semantics are currently a bit weird, but effectively this
flag is only ever set alongside __GFP_ZERO and __GFP_SKIP_KASAN.
If we run with init_on_free, we will zero out pages during
__free_pages_prepare(), to skip zeroing on the allocation path.
However, when allocating with __GFP_ZEROTAG set, post_alloc_hook() will
consequently not only skip clearing page content, but also skip clearing
tag memory.
Not clearing tags through __GFP_ZEROTAGS is irrelevant for most pages that
will get mapped to user space through set_pte_at() later: set_pte_at() and
friends will detect that the tags have not been initialized yet
(PG_mte_tagged not set), and initialize them.
However, for the huge zero folio, which will be mapped through a PMD
marked as special, this initialization will not be performed, ending up
exposing whatever tags were still set for the pages.
The docs (Documentation/arch/arm64/memory-tagging-extension.rst) state
that allocation tags are set to 0 when a page is first mapped to user
space. That no longer holds with the huge zero folio when init_on_free is
enabled.
Fix it by decoupling __GFP_ZEROTAGS from __GFP_ZERO, passing to
tag_clear_highpages() whether we want to also clear page content.
Invert the meaning of the tag_clear_highpages() return value to have
clearer semantics.
Reproduced with the huge zero folio by modifying the check_buffer_fill
arm64/mte selftest to use a 2 MiB area, after making sure that pages have
a non-0 tag set when freeing (note that, during boot, we will not actually
initialize tags, but only set KASAN_TAG_KERNEL in the page flags).
$ ./check_buffer_fill
1..20
...
not ok 17 Check initial tags with private mapping, sync error mode and mmap memory
not ok 18 Check initial tags with private mapping, sync error mode and mmap/mprotect memory
...
This code needs more cleanups; we'll tackle that next, like
decoupling __GFP_ZEROTAGS from __GFP_SKIP_KASAN.
[akpm@linux-foundation.org: s/__GPF_ZERO/__GFP_ZERO/, per David]
Link: https://lore.kernel.org/20260421-zerotags-v2-1-05cb1035482e@kernel.org
Fixes: adfb6609c6 ("mm/huge_memory: initialise the tags of the huge zero folio")
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Lance Yang <lance.yang@linux.dev>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Liam Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Will Deacon <will@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
59 lines
1.4 KiB
C
59 lines
1.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Based on arch/arm/include/asm/page.h
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*
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* Copyright (C) 1995-2003 Russell King
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* Copyright (C) 2012 ARM Ltd.
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*/
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#ifndef __ASM_PAGE_H
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#define __ASM_PAGE_H
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#include <asm/page-def.h>
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#ifndef __ASSEMBLER__
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#include <linux/personality.h> /* for READ_IMPLIES_EXEC */
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#include <linux/types.h> /* for gfp_t */
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#include <asm/pgtable-types.h>
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struct page;
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struct vm_area_struct;
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extern void copy_page(void *to, const void *from);
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extern void clear_page(void *to);
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void copy_user_highpage(struct page *to, struct page *from,
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unsigned long vaddr, struct vm_area_struct *vma);
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#define __HAVE_ARCH_COPY_USER_HIGHPAGE
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void copy_highpage(struct page *to, struct page *from);
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#define __HAVE_ARCH_COPY_HIGHPAGE
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struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
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unsigned long vaddr);
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#define vma_alloc_zeroed_movable_folio vma_alloc_zeroed_movable_folio
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bool tag_clear_highpages(struct page *to, int numpages, bool clear_pages);
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#define __HAVE_ARCH_TAG_CLEAR_HIGHPAGES
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#define copy_user_page(to, from, vaddr, pg) copy_page(to, from)
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typedef struct page *pgtable_t;
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int pfn_is_map_memory(unsigned long pfn);
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#include <asm/memory.h>
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#endif /* !__ASSEMBLER__ */
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#ifdef CONFIG_ARM64_MTE
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#define VMA_DATA_DEFAULT_FLAGS append_vma_flags(VMA_DATA_FLAGS_TSK_EXEC, \
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VMA_MTE_ALLOWED_BIT)
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#else
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#define VMA_DATA_DEFAULT_FLAGS VMA_DATA_FLAGS_TSK_EXEC
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#endif
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#include <asm-generic/getorder.h>
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#endif
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