linux-kernel - [PATCH xen 2/2] xen: update system time immediately when VCPUOP_register_vcpu

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Date:   Tue, 12 Oct 2021 00:24:28 -0700
From:   Dongli Zhang <dongli.zhang@...cle.com>
To:     xen-devel@...ts.xenproject.org
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        boris.ostrovsky@...cle.com, jgross@...e.com,
        sstabellini@...nel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, hpa@...or.com, andrew.cooper3@...rix.com,
        george.dunlap@...rix.com, iwj@...project.org, jbeulich@...e.com,
        julien@....org, wl@....org, joe.jin@...cle.com
Subject: [PATCH xen 2/2] xen: update system time immediately when VCPUOP_register_vcpu_info

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@...cle.com>
Signed-off-by: Dongli Zhang <dongli.zhang@...cle.com>
---
 xen/common/domain.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/xen/common/domain.c b/xen/common/domain.c
index 40d67ec342..c879f6723b 100644
--- 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);
+
         break;
     }
 
-- 
2.17.1