Messages in this thread Patch in this message | | | From | Radim Krčmář <> | Subject | [RFC PATCH 0/2] kvmclock: fix ABI breakage from PVCLOCK_COUNTS_FROM_ZERO. | Date | Fri, 18 Sep 2015 17:54:28 +0200 |
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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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