kvm: x86: fix kvmclock update protocol

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The kvmclock spec says that the host will increment a version field to
an odd number, then update stuff, then increment it to an even number.
The host is buggy and doesn't do this, and the result is observable
when one vcpu reads another vcpu's kvmclock data.

There's no good way for a guest kernel to keep its vdso from reading
a different vcpu's kvmclock data, but we don't need to care about
changing VCPUs as long as we read a consistent data from kvmclock.
(VCPU can change outside of this loop too, so it doesn't matter if we
return a value not fit for this VCPU.)

Based on a patch by Radim Krčmář.

Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Acked-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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Radim Krčmář 2015-03-25 12:08:14 +01:00 • committed by Paolo Bonzini

parent b787f68c36

commit 5dca0d9147

1 changed files with 28 additions and 5 deletions

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arch/x86/kvm/x86.c

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