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Commit 878854a3 authored by Nathan Lynch's avatar Nathan Lynch Committed by Catalin Marinas
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arm64: VDSO: fix coarse clock monotonicity regression 



Since 906c5557 ("timekeeping: Copy the shadow-timekeeper over the
real timekeeper last") it has become possible on arm64 to:

- Obtain a CLOCK_MONOTONIC_COARSE or CLOCK_REALTIME_COARSE timestamp
  via syscall.
- Subsequently obtain a timestamp for the same clock ID via VDSO which
  predates the first timestamp (by one jiffy).

This is because arm64's update_vsyscall is deriving the coarse time
using the __current_kernel_time interface, when it should really be
using the timekeeper object provided to it by the timekeeping core.
It happened to work before only because __current_kernel_time would
access the same timekeeper object which had been passed to
update_vsyscall.  This is no longer the case.

Signed-off-by: default avatarNathan Lynch <nathan_lynch@mentor.com>
Acked-by: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent f7644cbf

arch/arm64/kernel/vdso.c

+3 −4
Original line number Diff line number Diff line
@@ -199,16 +199,15 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, 
 */

void update_vsyscall(struct timekeeper *tk)

{

	struct timespec xtime_coarse;

	u32 use_syscall = strcmp(tk->tkr_mono.clock->name, "arch_sys_counter");



	++vdso_data->tb_seq_count;

	smp_wmb();



	xtime_coarse = __current_kernel_time();

	vdso_data->use_syscall			= use_syscall;

	vdso_data->xtime_coarse_sec		= xtime_coarse.tv_sec;

	vdso_data->xtime_coarse_nsec		= xtime_coarse.tv_nsec;

	vdso_data->xtime_coarse_sec		= tk->xtime_sec;

	vdso_data->xtime_coarse_nsec		= tk->tkr_mono.xtime_nsec >>

							tk->tkr_mono.shift;

	vdso_data->wtm_clock_sec		= tk->wall_to_monotonic.tv_sec;

	vdso_data->wtm_clock_nsec		= tk->wall_to_monotonic.tv_nsec;