From: Joerg Roedel <[email protected]>
The code for preallocate_vmalloc_pages() was written under the
assumption that the p4d_offset() and pud_offset() functions will perform
present checks before dereferencing the parent entries.
This assumption is wrong an leads to a bug in the code which causes the
physical address found in the PGD be used as a page-table page, even if
the PGD is not present.
So the code flow currently is:
pgd = pgd_offset_k(addr);
p4d = p4d_offset(pgd, addr);
if (p4d_none(*p4d))
p4d = p4d_alloc(&init_mm, pgd, addr);
This lacks a check for pgd_none() at least, the correct flow would be:
pgd = pgd_offset_k(addr);
if (pgd_none(*pgd))
p4d = p4d_alloc(&init_mm, pgd, addr);
else
p4d = p4d_offset(pgd, addr);
But this is the same flow that the p4d_alloc() and the pud_alloc()
functions use internally, so there is no need to duplicate them.
Remove the p?d_none() checks from the function and just call into
p4d_alloc() and pud_alloc() to correctly pre-allocate the PGD entries.
Reported-by: Jason A. Donenfeld <[email protected]>
Fixes: 6eb82f994026 ("x86/mm: Pre-allocate P4D/PUD pages for vmalloc area")
Signed-off-by: Joerg Roedel <[email protected]>
---
arch/x86/mm/init_64.c | 31 +++++++++++++------------------
1 file changed, 13 insertions(+), 18 deletions(-)
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 3f4e29a78f2b..449e071240e1 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1253,28 +1253,23 @@ static void __init preallocate_vmalloc_pages(void)
p4d_t *p4d;
pud_t *pud;
- p4d = p4d_offset(pgd, addr);
- if (p4d_none(*p4d)) {
- /* Can only happen with 5-level paging */
- p4d = p4d_alloc(&init_mm, pgd, addr);
- if (!p4d) {
- lvl = "p4d";
- goto failed;
- }
- }
+ lvl = "p4d";
+ p4d = p4d_alloc(&init_mm, pgd, addr);
+ if (!p4d)
+ goto failed;
+ /*
+ * With 5-level paging the P4D level is not folded. So the PGDs
+ * are now populated and there is no need to walk down to the
+ * PUD level.
+ */
if (pgtable_l5_enabled())
continue;
- pud = pud_offset(p4d, addr);
- if (pud_none(*pud)) {
- /* Ends up here only with 4-level paging */
- pud = pud_alloc(&init_mm, p4d, addr);
- if (!pud) {
- lvl = "pud";
- goto failed;
- }
- }
+ lvl = "pud";
+ pud = pud_alloc(&init_mm, p4d, addr);
+ if (!pud)
+ goto failed;
}
return;
--
2.26.2
