Commit 81fb8736 authored by Vincenzo Frascino's avatar Vincenzo Frascino Committed by Will Deacon
Browse files

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: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarVincenzo Frascino <vincenzo.frascino@arm.com>
[will: Use WRITE_ONCE(), move adr off COARSE path, renumber labels, use 'w' reg]
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 22e6c808

arch/arm64/include/asm/vdso_datapage.h

+1 −0
Original line number Diff line number Diff line
@@ -38,6 +38,7 @@ struct vdso_data { 
	__u32 tz_minuteswest;	/* Whacky timezone stuff */

	__u32 tz_dsttime;

	__u32 use_syscall;

	__u32 hrtimer_res;

};



#endif /* !__ASSEMBLY__ */

arch/arm64/kernel/asm-offsets.c

+1 −1
Original line number Diff line number Diff line
@@ -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);

arch/arm64/kernel/vdso.c

+3 −0
Original line number Diff line number Diff line
@@ -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;

arch/arm64/kernel/vdso/gettimeofday.S

+3 −4
Original line number Diff line number Diff line
@@ -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)

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