arm64: vdso: fix clocksource mask when extracting bottom 56 bits

The generic timer clocksource has 56 bits of precision and as such must
be masked appropriately after we have read it. The current mask
generated by a movn instruction is off by 4 bits, so we accidentally
include the top 4 bits in the final value.

This patch fixes the broken mask.

Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/kernel/vdso/gettimeofday.S b/arch/arm64/kernel/vdso/gettimeofday.S
index dcb8c20..05c1229 100644 (file)
--- a/arch/arm64/kernel/vdso/gettimeofday.S
+++ b/arch/arm64/kernel/vdso/gettimeofday.S
@@ -223,7 +223,7 @@ ENTRY(__do_get_tspec)
        /* Calculate cycle delta and convert to ns. */
        sub     x10, x9, x10
        /* We can only guarantee 56 bits of precision. */
        /* Calculate cycle delta and convert to ns. */
        sub     x10, x9, x10
        /* We can only guarantee 56 bits of precision. */

-       movn    x9, #0xff0, lsl #48
+       movn    x9, #0xff00, lsl #48

        and     x10, x9, x10
        mul     x10, x10, x14
        lsr     x10, x10, x15
        and     x10, x9, x10
        mul     x10, x10, x14
        lsr     x10, x10, x15