The guest may access the pv vcpu_time_info immediately after VCPUOP_register_vcpu_info. This is to borrow the idea of VCPUOP_register_vcpu_time_memory_area, where the force_update_vcpu_system_time() is called immediately when the new memory area is registered.
Otherwise, we may observe clock drift at the VM side if the VM accesses the clocksource immediately after VCPUOP_register_vcpu_info(). Reference: https://lists.xenproject.org/archives/html/xen-devel/2021-10/msg00571.html Cc: Joe Jin <joe....@oracle.com> Signed-off-by: Dongli Zhang <dongli.zh...@oracle.com> --- Changed since v1: - Implement force_update_vcpu_system_time() for ARM (suggested by Jan Beulich) While I have tested ARM compilation with aarch64-linux-gnu-gcc, I did not test on ARM platform. xen/arch/arm/time.c | 5 +++++ xen/common/domain.c | 2 ++ xen/include/asm-arm/time.h | 2 ++ 3 files changed, 9 insertions(+) diff --git a/xen/arch/arm/time.c b/xen/arch/arm/time.c index 7dbd363537..dec53b5f7d 100644 --- a/xen/arch/arm/time.c +++ b/xen/arch/arm/time.c @@ -351,6 +351,11 @@ void update_vcpu_system_time(struct vcpu *v) /* XXX update shared_info->wc_* */ } +void force_update_vcpu_system_time(struct vcpu *v) +{ + update_vcpu_system_time(v); +} + void domain_set_time_offset(struct domain *d, int64_t time_offset_seconds) { d->time_offset.seconds = time_offset_seconds; diff --git a/xen/common/domain.c b/xen/common/domain.c index 8b53c49d1e..d71fcab88c 100644 --- a/xen/common/domain.c +++ b/xen/common/domain.c @@ -1704,6 +1704,8 @@ long do_vcpu_op(int cmd, unsigned int vcpuid, XEN_GUEST_HANDLE_PARAM(void) arg) rc = map_vcpu_info(v, info.mfn, info.offset); domain_unlock(d); + force_update_vcpu_system_time(v); + break; } diff --git a/xen/include/asm-arm/time.h b/xen/include/asm-arm/time.h index 6b8fd839dd..4b401c1110 100644 --- a/xen/include/asm-arm/time.h +++ b/xen/include/asm-arm/time.h @@ -105,6 +105,8 @@ extern uint64_t ns_to_ticks(s_time_t ns); void preinit_xen_time(void); +void force_update_vcpu_system_time(struct vcpu *v); + #endif /* __ARM_TIME_H__ */ /* * Local variables: -- 2.17.1
