arm64: vdso: Fix clock_getres() for CLOCK_REALTIME

clock_getres() in the vDSO library has to preserve the same behaviour
of posix_get_hrtimer_res().

In particular, posix_get_hrtimer_res() does:

    sec = 0;
    ns = hrtimer_resolution;

where 'hrtimer_resolution' depends on whether or not high resolution
timers are enabled, which is a runtime decision.

The vDSO incorrectly returns the constant CLOCK_REALTIME_RES. Fix this
by exposing 'hrtimer_resolution' in the vDSO datapage and returning that
instead.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
[will: Use WRITE_ONCE(), move adr off COARSE path, renumber labels, use 'w' reg]
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm64/include/asm/vdso_datapage.h b/arch/arm64/include/asm/vdso_datapage.h
index 2b9a637..f89263c 100644 (file)
--- a/arch/arm64/include/asm/vdso_datapage.h
+++ b/arch/arm64/include/asm/vdso_datapage.h
@@ -38,6 +38,7 @@ struct vdso_data {
        __u32 tz_minuteswest;   /* Whacky timezone stuff */
        __u32 tz_dsttime;
        __u32 use_syscall;
+       __u32 hrtimer_res;
 };
 
 #endif /* !__ASSEMBLY__ */

diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 7f40dcb..e10e2a5 100644 (file)
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -94,7 +94,7 @@ int main(void)
   DEFINE(CLOCK_REALTIME,       CLOCK_REALTIME);
   DEFINE(CLOCK_MONOTONIC,      CLOCK_MONOTONIC);
   DEFINE(CLOCK_MONOTONIC_RAW,  CLOCK_MONOTONIC_RAW);
-  DEFINE(CLOCK_REALTIME_RES,   MONOTONIC_RES_NSEC);
+  DEFINE(CLOCK_REALTIME_RES,   offsetof(struct vdso_data, hrtimer_res));
   DEFINE(CLOCK_REALTIME_COARSE,        CLOCK_REALTIME_COARSE);
   DEFINE(CLOCK_MONOTONIC_COARSE,CLOCK_MONOTONIC_COARSE);
   DEFINE(CLOCK_COARSE_RES,     LOW_RES_NSEC);

diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
index 9fb0c0c..42b7082 100644 (file)
--- a/arch/arm64/kernel/vdso.c
+++ b/arch/arm64/kernel/vdso.c
@@ -230,6 +230,9 @@ void update_vsyscall(struct timekeeper *tk)
        vdso_data->wtm_clock_sec                = tk->wall_to_monotonic.tv_sec;
        vdso_data->wtm_clock_nsec               = tk->wall_to_monotonic.tv_nsec;
 
+       /* Read without the seqlock held by clock_getres() */
+       WRITE_ONCE(vdso_data->hrtimer_res, hrtimer_resolution);
+
        if (!use_syscall) {
                /* tkr_mono.cycle_last == tkr_raw.cycle_last */
                vdso_data->cs_cycle_last        = tk->tkr_mono.cycle_last;

diff --git a/arch/arm64/kernel/vdso/gettimeofday.S b/arch/arm64/kernel/vdso/gettimeofday.S
index c39872a..21805e4 100644 (file)
--- a/arch/arm64/kernel/vdso/gettimeofday.S
+++ b/arch/arm64/kernel/vdso/gettimeofday.S
@@ -301,13 +301,14 @@ ENTRY(__kernel_clock_getres)
        ccmp    w0, #CLOCK_MONOTONIC_RAW, #0x4, ne
        b.ne    1f
 
-       ldr     x2, 5f
+       adr     vdso_data, _vdso_data
+       ldr     w2, [vdso_data, #CLOCK_REALTIME_RES]
        b       2f
 1:
        cmp     w0, #CLOCK_REALTIME_COARSE
        ccmp    w0, #CLOCK_MONOTONIC_COARSE, #0x4, ne
        b.ne    4f
-       ldr     x2, 6f
+       ldr     x2, 5f
 2:
        cbz     x1, 3f
        stp     xzr, x2, [x1]
@@ -321,8 +322,6 @@ ENTRY(__kernel_clock_getres)
        svc     #0
        ret
 5:
-       .quad   CLOCK_REALTIME_RES
-6:
        .quad   CLOCK_COARSE_RES
        .cfi_endproc
 ENDPROC(__kernel_clock_getres)