[PATCH v2 2/2] arm64: mte: DC {GVA,GZVA} shouldn't be used when DCZID_EL0.DZP == 1

[Reiji Watanabe]

Currently, mte_set_mem_tag_range() and mte_zero_clear_page_tags() use
DC {GVA,GZVA} unconditionally.  But, they should make sure that
DCZID_EL0.DZP, which indicates whether or not use of those instructions
is prohibited, is zero when using those instructions.
Use ST{G,ZG} instead when DCZID_EL0.DZP == 1.

Fixes: 013bb59dbb7c ("arm64: mte: handle tags zeroing at page allocation time")
Fixes: 3d0cca0b02ac ("kasan: speed up mte_set_mem_tag_range")
Signed-off-by: Reiji Watanabe <reijiw at google.com>
---
 arch/arm64/include/asm/mte-kasan.h | 8 +++++---
 arch/arm64/lib/mte.S               | 8 +++++++-
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/mte-kasan.h
index 22420e1f8c03..26e013e540ae 100644
--- a/arch/arm64/include/asm/mte-kasan.h
+++ b/arch/arm64/include/asm/mte-kasan.h
@@ -84,10 +84,12 @@ static inline void __dc_gzva(u64 p)
 static inline void mte_set_mem_tag_range(void *addr, size_t size, u8 tag,
 					 bool init)
 {
-	u64 curr, mask, dczid_bs, end1, end2, end3;
+	u64 curr, mask, dczid, dczid_bs, dczid_dzp, end1, end2, end3;
 
 	/* Read DC G(Z)VA block size from the system register. */
-	dczid_bs = 4ul << (read_cpuid(DCZID_EL0) & 0xf);
+	dczid = read_cpuid(DCZID_EL0);
+	dczid_bs = 4ul << (dczid & 0xf);
+	dczid_dzp = (dczid >> 4) & 1;
 
 	curr = (u64)__tag_set(addr, tag);
 	mask = dczid_bs - 1;
@@ -106,7 +108,7 @@ static inline void mte_set_mem_tag_range(void *addr, size_t size, u8 tag,
 	 */
 #define SET_MEMTAG_RANGE(stg_post, dc_gva)		\
 	do {						\
-		if (size >= 2 * dczid_bs) {		\
+		if (!dczid_dzp && size >= 2 * dczid_bs) {\
 			do {				\
 				curr = stg_post(curr);	\
 			} while (curr < end1);		\
diff --git a/arch/arm64/lib/mte.S b/arch/arm64/lib/mte.S
index e83643b3995f..e62c048af337 100644
--- a/arch/arm64/lib/mte.S
+++ b/arch/arm64/lib/mte.S
@@ -43,17 +43,23 @@ SYM_FUNC_END(mte_clear_page_tags)
  *	x0 - address to the beginning of the page
  */
 SYM_FUNC_START(mte_zero_clear_page_tags)
+	and	x0, x0, #(1 << MTE_TAG_SHIFT) - 1	// clear the tag
 	mrs	x1, dczid_el0
+	tbnz	x1, #4, 2f	// Branch if DC GZVA is prohibited
 	and	w1, w1, #0xf
 	mov	x2, #4
 	lsl	x1, x2, x1
-	and	x0, x0, #(1 << MTE_TAG_SHIFT) - 1	// clear the tag
 
 1:	dc	gzva, x0
 	add	x0, x0, x1
 	tst	x0, #(PAGE_SIZE - 1)
 	b.ne	1b
 	ret
+
+2:	stzg	x0, [x0], #16
+	tst	x0, #(PAGE_SIZE - 1)
+	b.ne	2b
+	ret
 SYM_FUNC_END(mte_zero_clear_page_tags)
 
 /*
-- 
2.34.0.rc0.344.g81b53c2807-goog