x86/mm/pageattr: Add a PUD error unwinding path

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>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

1 files changed, 58 insertions, 2 deletions

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 2a1308a8c072..1cbdbbc35b47 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;
 }