Re: [PATCH] arm64: clear_page() shouldn't use DC ZVA when DCZID_EL0.DZP == 1
From: Robin Murphy <robin.murphy@arm.com>
Date: 2021-10-26 11:23:47
On 2021-10-26 04:48, Reiji Watanabe wrote:
quoted hunk ↗ jump to hunk
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 <redacted> --- 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. */
Out of curiosity, what's this for? It's not like we need to worry about PAGE_SIZE or page addresses being misaligned. I don't really see why we'd need a different condition from the DC ZVA loop. Robin.
+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)
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