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Re: [PATCH RFC 05/10] x86: update GADDR based secondary time area
- To: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 18 Jan 2023 10:25:18 +0100
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- Cc: George Dunlap <George.Dunlap@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 18 Jan 2023 09:25:38 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 17.01.2023 21:31, Andrew Cooper wrote:
> On 19/10/2022 8:41 am, Jan Beulich wrote:
>> --- a/xen/arch/x86/time.c
>> +++ b/xen/arch/x86/time.c
>> @@ -1462,12 +1462,34 @@ static void __update_vcpu_system_time(st
>> v->arch.pv.pending_system_time = _u;
>> }
>>
>> +static void write_time_guest_area(struct vcpu_time_info *map,
>> + const struct vcpu_time_info *src)
>> +{
>> + /* 1. Update userspace version. */
>> + write_atomic(&map->version, src->version);
>
> version_update_begin()
Not really, no. src->version was already bumped, and the above is
the equivalent of
/* 2. Update all other userspace fields. */
__copy_to_guest(user_u, u, 1);
in pre-existing code (which also doesn't bump).
However, you point out a bug in patch 9: There I need to set the
version to ~0 between collect_time_info() and write_time_guest_area(),
to cover for the subsequent version_update_end(). (Using
version_update_begin() there wouldn't be correct, as
force_update_secondary_system_time() is used to first populate the
area, and we also shouldn't leave version at 2 once done, as that
might get in conflict with subsequent updates mirroring the version
from the "main" area.)
Jan
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