[PATCH] x86/mm: Fix populate_pgd()

[Andy Lutomirski]

I make an obvious error in populate_pgd() -- it would fail to correctly
populate the page tables when it allocated a new pud page.

Fixes: 360cb4d15567 ("x86/mm/cpa: In populate_pgd(), don't set the PGD entry until it's populated")
Reported-by: Valdis Kletnieks <Valdis.Kletnieks@xxxxxx>
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
---
 arch/x86/mm/pageattr.c | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 26c93c6e04a0..5ee7d1c794a4 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -984,8 +984,8 @@ static int populate_pmd(struct cpa_data *cpa,
 	return num_pages;
 }
 
-static int populate_pud(struct cpa_data *cpa, unsigned long start, pgd_t *pgd,
-			pgprot_t pgprot)
+static int populate_pud(struct cpa_data *cpa, unsigned long start,
+			pud_t *pud_page, pgprot_t pgprot)
 {
 	pud_t *pud;
 	unsigned long end;
@@ -1006,7 +1006,7 @@ static int populate_pud(struct cpa_data *cpa, unsigned long start, pgd_t *pgd,
 		cur_pages = (pre_end - start) >> PAGE_SHIFT;
 		cur_pages = min_t(int, (int)cpa->numpages, cur_pages);
 
-		pud = pud_offset(pgd, start);
+		pud = pud_page + pud_index(start);
 
 		/*
 		 * Need a PMD page?
@@ -1027,7 +1027,7 @@ static int populate_pud(struct cpa_data *cpa, unsigned long start, pgd_t *pgd,
 	if (cpa->numpages == cur_pages)
 		return cur_pages;
 
-	pud = pud_offset(pgd, start);
+	pud = pud_page + pud_index(start);
 	pud_pgprot = pgprot_4k_2_large(pgprot);
 
 	/*
@@ -1047,7 +1047,7 @@ static int populate_pud(struct cpa_data *cpa, unsigned long start, pgd_t *pgd,
 	if (start < end) {
 		int tmp;
 
-		pud = pud_offset(pgd, start);
+		pud = pud_page + pud_index(start);
 		if (pud_none(*pud))
 			if (alloc_pmd_page(pud))
 				return -1;
@@ -1069,7 +1069,7 @@ static int populate_pud(struct cpa_data *cpa, unsigned long start, pgd_t *pgd,
 static int populate_pgd(struct cpa_data *cpa, unsigned long addr)
 {
 	pgprot_t pgprot = __pgprot(_KERNPG_TABLE);
-	pud_t *pud = NULL;	/* shut up gcc */
+	pud_t *pud_page = NULL;	/* shut up gcc */
 	pgd_t *pgd_entry;
 	int ret;
 
@@ -1079,25 +1079,27 @@ static int populate_pgd(struct cpa_data *cpa, unsigned long addr)
 	 * Allocate a PUD page and hand it down for mapping.
 	 */
 	if (pgd_none(*pgd_entry)) {
-		pud = (pud_t *)get_zeroed_page(GFP_KERNEL | __GFP_NOTRACK);
-		if (!pud)
+		pud_page = (pud_t *)get_zeroed_page(GFP_KERNEL | __GFP_NOTRACK);
+		if (!pud_page)
 			return -1;
 	}
 
 	pgprot_val(pgprot) &= ~pgprot_val(cpa->mask_clr);
 	pgprot_val(pgprot) |=  pgprot_val(cpa->mask_set);
 
-	ret = populate_pud(cpa, addr, pgd_entry, pgprot);
+	ret = populate_pud(cpa, addr,
+			   pud_page ?: (pud_t *)pgd_page_vaddr(*pgd_entry),
+			   pgprot);
 	if (ret < 0) {
-		if (pud)
-			free_page((unsigned long)pud);
+		if (pud_page)
+			free_page((unsigned long)pud_page);
 		unmap_pud_range(pgd_entry, addr,
 				addr + (cpa->numpages << PAGE_SHIFT));
 		return ret;
 	}
 
-	if (pud)
-		set_pgd(pgd_entry, __pgd(__pa(pud) | _KERNPG_TABLE));
+	if (pud_page)
+		set_pgd(pgd_entry, __pgd(__pa(pud_page) | _KERNPG_TABLE));
 
 	cpa->numpages = ret;
 	return 0;
-- 
2.7.4


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