[PATCH 4.14 125/167] arm64: proc: Set PTE_NG for table entries to avoid traversing them twice

Greg Kroah-Hartman
2018-02-21T12:48:56Z

From: Will Deacon <will.deacon@arm.com>

commit 2ce77f6d8a9ae9ce6d80397d88bdceb84a2004cd upstream.

When KASAN is enabled, the swapper page table contains many identical
mappings of the zero page, which can lead to a stall during boot whilst
the G -> nG code continually walks the same page table entries looking
for global mappings.

This patch sets the nG bit (bit 11, which is IGNORED) in table entries
after processing the subtree so we can easily skip them if we see them
a second time.

Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm64/mm/proc.S | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)

--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -190,7 +190,8 @@ ENDPROC(idmap_cpu_replace_ttbr1)
dc cvac, cur_\()\type\()p // Ensure any existing dirty
dmb sy // lines are written back before
ldr \type, [cur_\()\type\()p] // loading the entry
- tbz \type, #0, next_\()\type // Skip invalid entries
+ tbz \type, #0, skip_\()\type // Skip invalid and
+ tbnz \type, #11, skip_\()\type // non-global entries
.endm

.macro __idmap_kpti_put_pgtable_ent_ng, type
@@ -249,8 +250,9 @@ ENTRY(idmap_kpti_install_ng_mappings)
add end_pgdp, cur_pgdp, #(PTRS_PER_PGD * 8)
do_pgd: __idmap_kpti_get_pgtable_ent pgd
tbnz pgd, #1, walk_puds
- __idmap_kpti_put_pgtable_ent_ng pgd
next_pgd:
+ __idmap_kpti_put_pgtable_ent_ng pgd
+skip_pgd:
add cur_pgdp, cur_pgdp, #8
cmp cur_pgdp, end_pgdp
b.ne do_pgd
@@ -278,8 +280,9 @@ walk_puds:
add end_pudp, cur_pudp, #(PTRS_PER_PUD * 8)
do_pud: __idmap_kpti_get_pgtable_ent pud
tbnz pud, #1, walk_pmds
- __idmap_kpti_put_pgtable_ent_ng pud
next_pud:
+ __idmap_kpti_put_pgtable_ent_ng pud
+skip_pud:
add cur_pudp, cur_pudp, 8
cmp cur_pudp, end_pudp
b.ne do_pud
@@ -298,8 +301,9 @@ walk_pmds:
add end_pmdp, cur_pmdp, #(PTRS_PER_PMD * 8)
do_pmd: __idmap_kpti_get_pgtable_ent pmd
tbnz pmd, #1, walk_ptes
- __idmap_kpti_put_pgtable_ent_ng pmd
next_pmd:
+ __idmap_kpti_put_pgtable_ent_ng pmd
+skip_pmd:
add cur_pmdp, cur_pmdp, #8
cmp cur_pmdp, end_pmdp
b.ne do_pmd
@@ -317,7 +321,7 @@ walk_ptes:
add end_ptep, cur_ptep, #(PTRS_PER_PTE * 8)
do_pte: __idmap_kpti_get_pgtable_ent pte
__idmap_kpti_put_pgtable_ent_ng pte
-next_pte:
+skip_pte:
add cur_ptep, cur_ptep, #8
cmp cur_ptep, end_ptep
b.ne do_pte