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Re: [PATCH xen 2/2] xen: update system time immediately when VCPUOP_register_vcpu_info
- To: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 12 Oct 2021 10:40:23 +0200
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- Delivery-date: Tue, 12 Oct 2021 08:40:42 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 12.10.2021 09:24, Dongli Zhang wrote:
> 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().
>
> Cc: Joe Jin <joe.jin@xxxxxxxxxx>
> Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
While I agree with the change in principle, ...
> --- a/xen/common/domain.c
> +++ b/xen/common/domain.c
> @@ -1695,6 +1695,8 @@ 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);
... I'm afraid you're breaking the Arm build here. Arm will first need
to gain this function.
Jan
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