Commit-ID: 530dd8d4b9daf77e3e5d145a26210d91ced954c7
Gitweb: http://git.kernel.org/tip/530dd8d4b9daf77e3e5d145a26210d91ced954c7
Author: Andy Lutomirski <[email protected]>
AuthorDate: Fri, 22 Jul 2016 21:58:08 -0700
Committer: Ingo Molnar <[email protected]>
CommitDate: Sat, 23 Jul 2016 21:13:25 +0200
x86/mm/cpa: Fix populate_pgd(): Stop trying to deallocate failed PUDs
Valdis Kletnieks bisected a boot failure back to this recent commit:
360cb4d15567 ("x86/mm/cpa: In populate_pgd(), don't set the PGD entry until
it's populated")
I broke the case where a PUD table got allocated -- populate_pud()
would wander off a pgd_none entry and get lost. I'm not sure how
this survived my testing.
Fix the original issue in a much simpler way. The problem
was that, if we allocated a PUD table, failed to populate it, and
freed it, another CPU could potentially keep using the PGD entry we
installed (either by copying it via vmalloc_fault or by speculatively
caching it). There's a straightforward fix: simply leave the
top-level entry in place if this happens. This can't waste any
significant amount of memory -- there are at most 256 entries like
this systemwide and, as a practical matter, if we hit this failure
path repeatedly, we're likely to reuse the same page anyway.
For context, this is a reversion with this hunk added in:
if (ret < 0) {
+ /*
+ * Leave the PUD page in place in case some other CPU or thread
+ * already found it, but remove any useless entries we just
+ * added to it.
+ */
- unmap_pgd_range(cpa->pgd, addr,
+ unmap_pud_range(pgd_entry, addr,
addr + (cpa->numpages << PAGE_SHIFT));
return ret;
}
This effectively open-codes what the now-deleted unmap_pgd_range()
function used to do except that unmap_pgd_range() used to try to
free the page as well.
Reported-by: Valdis Kletnieks <[email protected]>
Signed-off-by: Andy Lutomirski <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Luis R. Rodriguez <[email protected]>
Cc: Mike Krinkin <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Toshi Kani <[email protected]>
Link:
http://lkml.kernel.org/r/21cbc2822aa18aa812c0215f4231dbf5f65afa7f.1469249789.git.l...@kernel.org
Signed-off-by: Ingo Molnar <[email protected]>
---
arch/x86/mm/pageattr.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 26c93c6..2bc6ea1 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -1082,6 +1082,8 @@ static int populate_pgd(struct cpa_data *cpa, unsigned
long addr)
pud = (pud_t *)get_zeroed_page(GFP_KERNEL | __GFP_NOTRACK);
if (!pud)
return -1;
+
+ set_pgd(pgd_entry, __pgd(__pa(pud) | _KERNPG_TABLE));
}
pgprot_val(pgprot) &= ~pgprot_val(cpa->mask_clr);
@@ -1089,16 +1091,11 @@ static int populate_pgd(struct cpa_data *cpa, unsigned
long addr)
ret = populate_pud(cpa, addr, pgd_entry, pgprot);
if (ret < 0) {
- if (pud)
- free_page((unsigned long)pud);
unmap_pud_range(pgd_entry, addr,
addr + (cpa->numpages << PAGE_SHIFT));
return ret;
}
- if (pud)
- set_pgd(pgd_entry, __pgd(__pa(pud) | _KERNPG_TABLE));
-
cpa->numpages = ret;
return 0;
}
