]> git.proxmox.com Git - mirror_ubuntu-hirsute-kernel.git/commitdiff
x86/kvmclock: set offset for kvm unstable clock
authorPavel Tatashin <pasha.tatashin@soleen.com>
Sat, 26 Jan 2019 17:49:56 +0000 (12:49 -0500)
committerPaolo Bonzini <pbonzini@redhat.com>
Wed, 20 Feb 2019 21:48:19 +0000 (22:48 +0100)
VMs may show incorrect uptime and dmesg printk offsets on hypervisors with
unstable clock. The problem is produced when VM is rebooted without exiting
from qemu.

The fix is to calculate clock offset not only for stable clock but for
unstable clock as well, and use kvm_sched_clock_read() which substracts
the offset for both clocks.

This is safe, because pvclock_clocksource_read() does the right thing and
makes sure that clock always goes forward, so once offset is calculated
with unstable clock, we won't get new reads that are smaller than offset,
and thus won't get negative results.

Thank you Jon DeVree for helping to reproduce this issue.

Fixes: 857baa87b642 ("sched/clock: Enable sched clock early")
Cc: stable@vger.kernel.org
Reported-by: Dominique Martinet <asmadeus@codewreck.org>
Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
arch/x86/kernel/kvmclock.c

index e811d4d1c824718acd6b4bef7acba2565290bcd3..d908a37bf3f3a25f57a51ed50d508acbfe7b902b 100644 (file)
@@ -104,12 +104,8 @@ static u64 kvm_sched_clock_read(void)
 
 static inline void kvm_sched_clock_init(bool stable)
 {
-       if (!stable) {
-               pv_ops.time.sched_clock = kvm_clock_read;
+       if (!stable)
                clear_sched_clock_stable();
-               return;
-       }
-
        kvm_sched_clock_offset = kvm_clock_read();
        pv_ops.time.sched_clock = kvm_sched_clock_read;