x86: fix PAE pmd_bad bootup warning (aeed5fce) · Commits · 戴 / test

Fix warning from pmd_bad() at bootup on a HIGHMEM64G HIGHPTE x86_32. That came from x86: debug pmd_bad(); but we understand now that the typecasting was wrong for PAE in the previous version: pagetable pages above 4GB looked bad and stopped Arjan from booting. And revert that x86: fix pmd_bad and pud_bad to support huge pages. It was the wrong way round: we shouldn't weaken every pmd_bad and pud_bad check to let huge pages slip through - in part they check that we _don't_ have a huge page where it's not expected. Put the x86 pmd_bad() and pud_bad() definitions back to what they have long been: they can be improved (x86_32 should use PTE_MASK, to stop PAE thinking junk in the upper word is good; and x86_64 should follow x86_32's stricter comparison, to stop thinking any subset of required bits is good); but that should be a later patch. Fix Hans' good observation that follow_page() will never find pmd_huge() because that would have already failed the pmd_bad test: test pmd_huge in between the pmd_none and pmd_bad tests. Tighten x86's pmd_huge() check? No, once it's a hugepage entry, it can get quite far from a good pmd: for example, PROT_NONE leaves it with only ACCESSED of the KERN_PGTABLE bits. However... though follow_page() contains this and another test for huge pages, so it's nice to keep it working on them, where does it actually get called on a huge page? get_user_pages() checks is_vm_hugetlb_page(vma) to to call alternative hugetlb processing, as does unmap_vmas() and others. Signed-off-by:

Hugh Dickins <hugh@veritas.com> Earlier-version-tested-by:

Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Jeff Chua <jeff.chua.linux@gmail.com> Cc: Hans Rosenfeld <hans.rosenfeld@amd.com> Cc: Arjan van de Ven <arjan@linux.intel.com> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

arch/x86/mm/pgtable_32.c

+0 −7

Original line number	Diff line number	Diff line
		@@ -172,10 +172,3 @@ void reserve_top_address(unsigned long reserve)
		__FIXADDR_TOP = -reserve - PAGE_SIZE;
		__VMALLOC_RESERVE += reserve;
		}

		int pmd_bad(pmd_t pmd)
		{
		WARN_ON_ONCE(pmd_bad_v1(pmd) != pmd_bad_v2(pmd));

		return pmd_bad_v1(pmd);
		}

include/asm-x86/pgtable_32.h

+1 −8

Original line number	Diff line number	Diff line
		@@ -88,14 +88,7 @@ extern unsigned long pg0[];
		/* To avoid harmful races, pmd_none(x) should check only the lower when PAE */
		#define pmd_none(x) (!(unsigned long)pmd_val((x)))
		#define pmd_present(x) (pmd_val((x)) & _PAGE_PRESENT)

		extern int pmd_bad(pmd_t pmd);

		#define pmd_bad_v1(x) \
		(_KERNPG_TABLE != (pmd_val((x)) & ~(PAGE_MASK \| _PAGE_USER)))
		#define pmd_bad_v2(x) \
		(_KERNPG_TABLE != (pmd_val((x)) & ~(PAGE_MASK \| _PAGE_USER \| \
		_PAGE_PSE \| _PAGE_NX)))
		#define pmd_bad(x) ((pmd_val(x) & (~PAGE_MASK & ~_PAGE_USER)) != _KERNPG_TABLE)

		#define pages_to_mb(x) ((x) >> (20-PAGE_SHIFT))

include/asm-x86/pgtable_64.h

+2 −4

Original line number	Diff line number	Diff line
		@@ -158,14 +158,12 @@ static inline unsigned long pgd_bad(pgd_t pgd)

		static inline unsigned long pud_bad(pud_t pud)
		{
		return pud_val(pud) &
		~(PTE_MASK \| _KERNPG_TABLE \| _PAGE_USER \| _PAGE_PSE \| _PAGE_NX);
		return pud_val(pud) & ~(PTE_MASK \| _KERNPG_TABLE \| _PAGE_USER);
		}

		static inline unsigned long pmd_bad(pmd_t pmd)
		{
		return pmd_val(pmd) &
		~(PTE_MASK \| _KERNPG_TABLE \| _PAGE_USER \| _PAGE_PSE \| _PAGE_NX);
		return pmd_val(pmd) & ~(PTE_MASK \| _KERNPG_TABLE \| _PAGE_USER);
		}

		#define pte_none(x) (!pte_val((x)))

mm/memory.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -969,7 +969,7 @@ struct page follow_page(struct vm_area_struct vma, unsigned long address,
		goto no_page_table;

		pmd = pmd_offset(pud, address);
		if (pmd_none(pmd) \|\| unlikely(pmd_bad(pmd)))
		if (pmd_none(*pmd))
		goto no_page_table;

		if (pmd_huge(*pmd)) {
		@@ -978,6 +978,9 @@ struct page follow_page(struct vm_area_struct vma, unsigned long address,
		goto out;
		}

		if (unlikely(pmd_bad(*pmd)))
		goto no_page_table;

		ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
		if (!ptep)
		goto out;

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