linux-kernel - [PATCH] x86/mm: Skip the hypervisor range when walking PGD

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Date:	Thu,  5 Nov 2015 13:56:35 -0500
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org, linux@...elenboom.it,
	xen-devel@...ts.xen.org, boris.ostrovsky@...cle.com
Subject: [PATCH] x86/mm: Skip the hypervisor range when walking PGD

The range between 0xffff800000000000 and 0xffff87ffffffffff is reserved
for hypervisor and therefore we should not try to follow PGD's indexes
corresponding to those addresses.

While this has alsways been a problem, with commit e1a58320a38d ("x86/mm:
Warn on W^X mappings") ptdump_walk_pgd_level_core() can now be called
during boot, causing a PV Xen guest to crash.

Reported-by: Sander Eikelenboom <linux@...elenboom.it>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
---
 arch/x86/mm/dump_pagetables.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c
index 1bf417e..756c921 100644
--- a/arch/x86/mm/dump_pagetables.c
+++ b/arch/x86/mm/dump_pagetables.c
@@ -362,8 +362,13 @@ static void ptdump_walk_pgd_level_core(struct seq_file *m, pgd_t *pgd,
 				       bool checkwx)
 {
 #ifdef CONFIG_X86_64
+/* ffff800000000000 - ffff87ffffffffff is reserved for hypervisor */
+#define is_hypervisor_range(idx) (paravirt_enabled() && \
+				  (((idx) >= pgd_index(__PAGE_OFFSET) - 16) && \
+				   ((idx) < pgd_index(__PAGE_OFFSET))))
 	pgd_t *start = (pgd_t *) &init_level4_pgt;
 #else
+#define is_hypervisor_range(idx)   0
 	pgd_t *start = swapper_pg_dir;
 #endif
 	pgprotval_t prot;
@@ -381,7 +386,7 @@ static void ptdump_walk_pgd_level_core(struct seq_file *m, pgd_t *pgd,
 
 	for (i = 0; i < PTRS_PER_PGD; i++) {
 		st.current_address = normalize_addr(i * PGD_LEVEL_MULT);
-		if (!pgd_none(*start)) {
+		if (!pgd_none(*start) && !is_hypervisor_range(i)) {
 			if (pgd_large(*start) || !pgd_present(*start)) {
 				prot = pgd_flags(*start);
 				note_page(m, &st, __pgprot(prot), 1);
-- 
1.9.3

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