linux-kernel - [PATCH 5.16 0237/1039] arm64: clear_page() shouldnt use DC ZVA when DCZID

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Message-Id: <20220124184133.283001988@linuxfoundation.org>
Date:   Mon, 24 Jan 2022 19:33:46 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Reiji Watanabe <reijiw@...gle.com>,
        Robin Murphy <robin.murphy@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.16 0237/1039] arm64: clear_page() shouldnt use DC ZVA when DCZID_EL0.DZP == 1

From: Reiji Watanabe <reijiw@...gle.com>

[ Upstream commit f0616abd4e67143b45b04b565839148458857347 ]

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 STNP instead when DCZID_EL0.DZP == 1.

Fixes: f27bb139c387 ("arm64: Miscellaneous library functions")
Signed-off-by: Reiji Watanabe <reijiw@...gle.com>
Reviewed-by: Robin Murphy <robin.murphy@....com>
Link: https://lore.kernel.org/r/20211206004736.1520989-2-reijiw@google.com
Signed-off-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/arm64/lib/clear_page.S | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/arm64/lib/clear_page.S b/arch/arm64/lib/clear_page.S
index b84b179edba3a..1fd5d790ab800 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 ZVA is prohibited */
 	and	w1, w1, #0xf
 	mov	x2, #4
 	lsl	x1, x2, x1
@@ -25,5 +26,14 @@ SYM_FUNC_START_PI(clear_page)
 	tst	x0, #(PAGE_SIZE - 1)
 	b.ne	1b
 	ret
+
+2:	stnp	xzr, xzr, [x0]
+	stnp	xzr, xzr, [x0, #16]
+	stnp	xzr, xzr, [x0, #32]
+	stnp	xzr, xzr, [x0, #48]
+	add	x0, x0, #64
+	tst	x0, #(PAGE_SIZE - 1)
+	b.ne	2b
+	ret
 SYM_FUNC_END_PI(clear_page)
 EXPORT_SYMBOL(clear_page)
-- 
2.34.1