This patch series will be disabling PVCLOCK_COUNTS_FROM_ZERO flag and is
RFC because I haven't explored many potential problems or tested it.
[1/2] uses a different algorithm in the guest to start counting from 0.
[2/2] stops exposing PVCLOCK_COUNTS_FROM_ZERO in the hypervisor.
A viable alternative would be to implement opt-in features in kvm clock.
And because we probably only broke one old user (the infamous SLES 10), a
workaround like this is also possible: (but I'd rather not do that)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a60bdbccff51..ae9049248aaf 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2007,7 +2007,8 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
ka->boot_vcpu_runs_old_kvmclock = tmp;
- ka->kvmclock_offset = -get_kernel_ns();
+ if (!ka->boot_vcpu_runs_old_kvmclock)
+ ka->kvmclock_offset = -get_kernel_ns();
}
vcpu->arch.time = data;
Radim Krčmář (2):
x86: kvmclock: abolish PVCLOCK_COUNTS_FROM_ZERO
Revert "KVM: x86: zero kvmclock_offset when vcpu0 initializes kvmclock
system MSR"
arch/x86/include/asm/pvclock-abi.h | 1 +
arch/x86/kernel/kvmclock.c | 46 +++++++++++++++++++++++++++++---------
arch/x86/kvm/x86.c | 4 ----
3 files changed, 36 insertions(+), 15 deletions(-)
--
2.5.2
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