[PATCH] arm64: clear_page() shouldn't use DC ZVA when DCZID_EL0.DZP == 1

[Reiji Watanabe]

Currently, clear_page() uses DC ZVA instruction unconditionally.  But it
should make sure that DCZID_EL0.DZP, which indicates whether or not use
of DC ZVA instruction is prohibited, is zero when using the instruction.
Use stp as memset does instead when DCZID_EL0.DZP == 1.

Signed-off-by: Reiji Watanabe <reijiw at google.com>
---
 arch/arm64/lib/clear_page.S | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/arm64/lib/clear_page.S b/arch/arm64/lib/clear_page.S
index b84b179edba3..7ce1bfa4081c 100644
--- a/arch/arm64/lib/clear_page.S
+++ b/arch/arm64/lib/clear_page.S
@@ -16,6 +16,7 @@
  */
 SYM_FUNC_START_PI(clear_page)
 	mrs	x1, dczid_el0
+	tbnz	x1, #4, 2f	/* Branch if DC GVA is prohibited */
 	and	w1, w1, #0xf
 	mov	x2, #4
 	lsl	x1, x2, x1
@@ -25,5 +26,15 @@ SYM_FUNC_START_PI(clear_page)
 	tst	x0, #(PAGE_SIZE - 1)
 	b.ne	1b
 	ret
+
+2:	mov	x1, #(PAGE_SIZE)
+	sub	x0, x0, #16	/* Pre-bias. */
+3:	stp	xzr, xzr, [x0, #16]
+	stp	xzr, xzr, [x0, #32]
+	stp	xzr, xzr, [x0, #48]
+	stp	xzr, xzr, [x0, #64]!
+	subs	x1, x1, #64
+	b.gt	3b
+	ret
 SYM_FUNC_END_PI(clear_page)
 EXPORT_SYMBOL(clear_page)
-- 
2.33.0.1079.g6e70778dc9-goog