[PATCH 08/11] x86, pageattr: Add a PUD error unwinding path

Borislav Petkov
2013-09-19T14:57:40Z

From: Borislav Petkov <bp@suse.de>

In case we encounter an error during the mapping of a region, we want to
unwind what we've established so far exactly the way we did the mapping.
This is the PUD part kept deliberately small for easier review.

Signed-off-by: Borislav Petkov <bp@suse.de>
---
arch/x86/mm/pageattr.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 58 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 02cf97b3bb7c..a0d2e90ad62b 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -666,6 +666,51 @@ static int split_large_page(pte_t *kpte, unsigned long address)
return 0;
}

+#define unmap_pmd_range(pud, start, pre_end) do {} while (0)
+
+static void unmap_pud_range(pgd_t *pgd, unsigned long start, unsigned long end)
+{
+ pud_t *pud = pud_offset(pgd, start);
+
+ /*
+ * Not on a GB page boundary?
+ */
+ if (start & (PUD_SIZE - 1)) {
+ unsigned long next_page = (start + PUD_SIZE) & PUD_MASK;
+ unsigned long pre_end = min_t(unsigned long, end, next_page);
+
+ unmap_pmd_range(pud, start, pre_end);
+
+ start = pre_end;
+ pud++;
+ }
+
+ /*
+ * Try to unmap in 1G chunks?
+ */
+ while (end - start >= PUD_SIZE) {
+
+ if (pud_large(*pud))
+ pud_clear(pud);
+ else
+ unmap_pmd_range(pud, start, start + PUD_SIZE);
+
+ start += PUD_SIZE;
+ pud++;
+ }
+
+ /*
+ * 2M leftovers?
+ */
+ if (start < end)
+ unmap_pmd_range(pud, start, end);
+
+ /*
+ * No need to try to free the PUD page because we'll free it in
+ * populate_pgd's error path
+ */
+}
+
static int alloc_pte_page(pmd_t *pmd)
{
pte_t *pte = (pte_t *)get_zeroed_page(GFP_KERNEL | __GFP_NOTRACK);
@@ -883,9 +928,20 @@ static int populate_pgd(struct cpa_data *cpa, unsigned long addr)
pgprot_val(pgprot) |= pgprot_val(cpa->mask_set);

ret = populate_pud(cpa, addr, pgd_entry, pgprot);
- if (ret < 0)
- return ret;
+ if (ret < 0) {
+ unmap_pud_range(pgd_entry, addr,
+ addr + (cpa->numpages << PAGE_SHIFT));

+ if (allocd_pgd) {
+ /*
+ * If I allocated this PUD page, I can just as well
+ * free it in this error path.
+ */
+ pgd_clear(pgd_entry);
+ free_page((unsigned long)pud);
+ }
+ return ret;
+ }
cpa->numpages = ret;
return 0;
}
--
1.8.4