From 45a7905fc48f6079932e77d64237cf7f008db5f4 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Thu, 29 Nov 2012 22:33:29 +0000 Subject: [PATCH] arm64: vdso: defer shifting of nanosecond component of timespec Shifting the nanosecond component of the computed timespec early can lead to sub-ns inaccuracies when using the truncated value as input to further arithmetic for things like conversions to monotonic time. This patch defers the timespec shifting until after the final value has been computed. Reported-by: John Stultz Signed-off-by: Will Deacon Signed-off-by: Catalin Marinas --- arch/arm64/kernel/vdso.c | 2 +- arch/arm64/kernel/vdso/gettimeofday.S | 8 ++++++-- 2 files changed, 7 insertions(+), 3 deletions(-) diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c index ba45794..c958cb8 100644 --- a/arch/arm64/kernel/vdso.c +++ b/arch/arm64/kernel/vdso.c @@ -239,7 +239,7 @@ void update_vsyscall(struct timekeeper *tk) if (!use_syscall) { vdso_data->cs_cycle_last = tk->clock->cycle_last; vdso_data->xtime_clock_sec = tk->xtime_sec; - vdso_data->xtime_clock_nsec = tk->xtime_nsec >> tk->shift; + vdso_data->xtime_clock_nsec = tk->xtime_nsec; vdso_data->cs_mult = tk->mult; vdso_data->cs_shift = tk->shift; vdso_data->wtm_clock_sec = tk->wall_to_monotonic.tv_sec; diff --git a/arch/arm64/kernel/vdso/gettimeofday.S b/arch/arm64/kernel/vdso/gettimeofday.S index 99b7d40..6681f40 100644 --- a/arch/arm64/kernel/vdso/gettimeofday.S +++ b/arch/arm64/kernel/vdso/gettimeofday.S @@ -66,6 +66,7 @@ ENTRY(__kernel_gettimeofday) /* Convert ns to us. */ mov x13, #1000 + lsl x13, x13, x12 udiv x11, x11, x13 stp x10, x11, [x0, #TVAL_TV_SEC] 2: @@ -136,11 +137,13 @@ ENTRY(__kernel_clock_gettime) 4: /* Add on wtm timespec. */ add x10, x10, x13 + lsl x14, x14, x12 add x11, x11, x14 /* Normalise the new timespec. */ mov x15, #NSEC_PER_SEC_LO16 movk x15, #NSEC_PER_SEC_HI16, lsl #16 + lsl x15, x15, x12 cmp x11, x15 b.lt 5f sub x11, x11, x15 @@ -152,6 +155,7 @@ ENTRY(__kernel_clock_gettime) sub x10, x10, #1 6: /* Store to the user timespec. */ + lsr x11, x11, x12 stp x10, x11, [x1, #TSPEC_TV_SEC] mov x0, xzr ret x2 @@ -204,7 +208,7 @@ ENDPROC(__kernel_clock_getres) * Clobbers the temporary registers (x9 - x15). * Returns: * - w9 = vDSO sequence counter - * - (x10, x11) = (ts->tv_sec, ts->tv_nsec) + * - (x10, x11) = (ts->tv_sec, shifted ts->tv_nsec) * - w12 = cs_shift */ ENTRY(__do_get_tspec) @@ -226,11 +230,11 @@ ENTRY(__do_get_tspec) movn x15, #0xff00, lsl #48 and x10, x15, x10 mul x10, x10, x11 - lsr x10, x10, x12 /* Use the kernel time to calculate the new timespec. */ mov x11, #NSEC_PER_SEC_LO16 movk x11, #NSEC_PER_SEC_HI16, lsl #16 + lsl x11, x11, x12 add x15, x10, x14 udiv x14, x15, x11 add x10, x13, x14 -- 2.7.4