From: Jan Beulich <jbeulich@suse.com>
To: Ian Jackson <iwj@xenproject.org>
Cc: Dongli Zhang <dongli.zhang@oracle.com>,
sstabellini@kernel.org, julien@xen.org,
Volodymyr_Babchuk@epam.com, andrew.cooper3@citrix.com,
george.dunlap@citrix.com, wl@xen.org, joe.jin@oracle.com,
xen-devel@lists.xenproject.org
Subject: Re: [PATCH v2 1/1] xen: update system time immediately when VCPUOP_register_vcpu_info
Date: Tue, 2 Nov 2021 17:36:36 +0100 [thread overview]
Message-ID: <ec809d19-670c-bc91-7b08-0cb7734f0d80@suse.com> (raw)
In-Reply-To: <24961.24756.236341.888900@mariner.uk.xensource.com>
On 02.11.2021 17:00, Ian Jackson wrote:
> Jan Beulich writes ("Re: [PATCH v2 1/1] xen: update system time immediately when VCPUOP_register_vcpu_info"):
>> On 25.10.2021 19:35, 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().
>>>
>>> Reference:
>>> https://lists.xenproject.org/archives/html/xen-devel/2021-10/msg00571.html
>>> Cc: Joe Jin <joe.jin@oracle.com>
>>> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
>>
>> Reviewed-by: Jan Beulich <jbeulich@suse.com>
>>
>> Ian - any thoughts towards 4.16 here either way?
>
> This looks like a bugfix to me, and the diff is certainly small. I am
> positively inclined. I would like to know what the risks are.
> Stefano says this does nothing on ARM so the risk would be to x86.
> Can you advise ?
I don't see any noteworthy risks - a call to a function gets added
in a 2nd place; the function itself has been working fine for years,
and it is fine to be used in this new context.
Jan
next prev parent reply other threads:[~2021-11-02 16:37 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-25 17:35 [PATCH v2 1/1] xen: update system time immediately when VCPUOP_register_vcpu_info Dongli Zhang
2021-10-28 21:07 ` Stefano Stabellini
2021-11-02 12:23 ` Jan Beulich
2021-11-02 16:00 ` Ian Jackson
2021-11-02 16:36 ` Jan Beulich [this message]
2021-11-02 16:48 ` Ian Jackson
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