linux-kernel - [PATCH 0/2] KVM: x86: do not mix raw and monotonic clocks in kvmclock

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Date:   Wed, 22 Jan 2020 15:22:31 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     mtosatti@...hat.com
Subject: [PATCH 0/2] KVM: x86: do not mix raw and monotonic clocks in kvmclock

Commit 53fafdbb8b21f ("KVM: x86: switch KVMCLOCK base to monotonic raw
clock") changed kvmclock to use tkr_raw instead of tkr_mono.  However,
the default kvmclock_offset for the VM was still based on the monotonic
clock and, if the raw clock drifted enough from the monotonic clock,
this could cause a negative system_time to be written to the guest's
struct pvclock.  RHEL5 does not like it and (if it boots fast enough to
observe a negative time value) it hangs.

This series fixes the issue by using the raw clock everywhere.

(And this, ladies and gentlemen, is why I was not applying patches to
the KVM tree.  I saw this before Christmas and could only reproduce it
today, since it requires almost 2 weeks of uptime to reproduce on my
machine.  Of course, once you have the reproducer the fix is relatively
easy to come up with).

Paolo

Paolo Bonzini (2):
  KVM: x86: reorganize pvclock_gtod_data members
  KVM: x86: use raw clock values consistently

 arch/x86/kvm/x86.c | 67 ++++++++++++++++++++++++++++--------------------------
 1 file changed, 35 insertions(+), 32 deletions(-)

-- 
1.8.3.1