[098/178] mm/vmalloc: fix HUGE_VMAP regression by enabling huge pages in vmalloc_to_page

Commit Message

Andrew Morton April 30, 2021, 5:58 a.m. UTC

From: Nicholas Piggin <[e-mail]>
Subject: mm/vmalloc: fix HUGE_VMAP regression by enabling huge pages in vmalloc_to_page

vmalloc_to_page returns NULL for addresses mapped by larger pages[*]. 
Whether or not a vmap is huge depends on the architecture details,
alignments, boot options, etc., which the caller can not be expected to
know.  Therefore HUGE_VMAP is a regression for vmalloc_to_page.

This change teaches vmalloc_to_page about larger pages, and returns the
struct page that corresponds to the offset within the large page.  This
makes the API agnostic to mapping implementation details.

[*] As explained by commit 029c54b095995 ("mm/vmalloc.c: huge-vmap:
    fail gracefully on unexpected huge vmap mappings")

[[e-mail]: sparc32: add stub pud_page define for walking huge vmalloc page tables]
  Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Nicholas Piggin <[e-mail]>
Reviewed-by: Miaohe Lin <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Ding Tianhong <[e-mail]>
Cc: "H. Peter Anvin" <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Michael Ellerman <[e-mail]>
Cc: Russell King <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Uladzislau Rezki (Sony) <[e-mail]>
Cc: Will Deacon <[e-mail]>
Cc: Stephen Rothwell <[e-mail]>
Cc: David S. Miller <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 arch/sparc/include/asm/pgtable_32.h |    3 +
 mm/vmalloc.c                        |   41 ++++++++++++++++----------
 2 files changed, 29 insertions(+), 15 deletions(-)

Patch

--- a/arch/sparc/include/asm/pgtable_32.h~mm-vmalloc-fix-huge_vmap-regression-by-enabling-huge-pages-in-vmalloc_to_page
+++ a/arch/sparc/include/asm/pgtable_32.h
@@ -321,6 +321,9 @@  static inline pte_t pte_modify(pte_t pte
 		pgprot_val(newprot));
 }
 
+/* only used by the huge vmap code, should never be called */
+#define pud_page(pud)			NULL
+
 struct seq_file;
 void mmu_info(struct seq_file *m);
 
--- a/mm/vmalloc.c~mm-vmalloc-fix-huge_vmap-regression-by-enabling-huge-pages-in-vmalloc_to_page
+++ a/mm/vmalloc.c
@@ -34,7 +34,7 @@ 
 #include <linux/bitops.h>
 #include <linux/rbtree_augmented.h>
 #include <linux/overflow.h>
-
+#include <linux/pgtable.h>
 #include <linux/uaccess.h>
 #include <asm/tlbflush.h>
 #include <asm/shmparam.h>
@@ -343,7 +343,9 @@  int is_vmalloc_or_module_addr(const void
 }
 
 /*
- * Walk a vmap address to the struct page it maps.
+ * Walk a vmap address to the struct page it maps. Huge vmap mappings will
+ * return the tail page that corresponds to the base page address, which
+ * matches small vmap mappings.
  */
 struct page *vmalloc_to_page(const void *vmalloc_addr)
 {
@@ -363,25 +365,33 @@  struct page *vmalloc_to_page(const void
 
 	if (pgd_none(*pgd))
 		return NULL;
+	if (WARN_ON_ONCE(pgd_leaf(*pgd)))
+		return NULL; /* XXX: no allowance for huge pgd */
+	if (WARN_ON_ONCE(pgd_bad(*pgd)))
+		return NULL;
+
 	p4d = p4d_offset(pgd, addr);
 	if (p4d_none(*p4d))
 		return NULL;
-	pud = pud_offset(p4d, addr);
+	if (p4d_leaf(*p4d))
+		return p4d_page(*p4d) + ((addr & ~P4D_MASK) >> PAGE_SHIFT);
+	if (WARN_ON_ONCE(p4d_bad(*p4d)))
+		return NULL;
 
-	/*
-	 * Don't dereference bad PUD or PMD (below) entries. This will also
-	 * identify huge mappings, which we may encounter on architectures
-	 * that define CONFIG_HAVE_ARCH_HUGE_VMAP=y. Such regions will be
-	 * identified as vmalloc addresses by is_vmalloc_addr(), but are
-	 * not [unambiguously] associated with a struct page, so there is
-	 * no correct value to return for them.
-	 */
-	WARN_ON_ONCE(pud_bad(*pud));
-	if (pud_none(*pud) || pud_bad(*pud))
+	pud = pud_offset(p4d, addr);
+	if (pud_none(*pud))
+		return NULL;
+	if (pud_leaf(*pud))
+		return pud_page(*pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
+	if (WARN_ON_ONCE(pud_bad(*pud)))
 		return NULL;
+
 	pmd = pmd_offset(pud, addr);
-	WARN_ON_ONCE(pmd_bad(*pmd));
-	if (pmd_none(*pmd) || pmd_bad(*pmd))
+	if (pmd_none(*pmd))
+		return NULL;
+	if (pmd_leaf(*pmd))
+		return pmd_page(*pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
+	if (WARN_ON_ONCE(pmd_bad(*pmd)))
 		return NULL;
 
 	ptep = pte_offset_map(pmd, addr);
@@ -389,6 +399,7 @@  struct page *vmalloc_to_page(const void
 	if (pte_present(pte))
 		page = pte_page(pte);
 	pte_unmap(ptep);
+
 	return page;
 }
 EXPORT_SYMBOL(vmalloc_to_page);