This is a note to let you know that I've just added the patch titled kvm: x86: Disable KVM_HC_CLOCK_PAIRING if tsc is in always catchup mode to the 5.16-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: kvm-x86-disable-kvm_hc_clock_pairing-if-tsc-is-in-al.patch and it can be found in the queue-5.16 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 7e6df81a4719def09302fe05e0e04ae3aea8efab Author: Anton Romanov <romanton@xxxxxxxxxx> Date: Wed Feb 16 18:26:54 2022 +0000 kvm: x86: Disable KVM_HC_CLOCK_PAIRING if tsc is in always catchup mode [ Upstream commit 3a55f729240a686aa8af00af436306c0cd532522 ] If vcpu has tsc_always_catchup set each request updates pvclock data. KVM_HC_CLOCK_PAIRING consumers such as ptp_kvm_x86 rely on tsc read on host's side and do hypercall inside pvclock_read_retry loop leading to infinite loop in such situation. v3: Removed warn Changed return code to KVM_EFAULT v2: Added warn Signed-off-by: Anton Romanov <romanton@xxxxxxxxxx> Message-Id: <20220216182653.506850-1-romanton@xxxxxxxxxx> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c6eb3e45e3d8..e8f495b9ae10 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -8770,6 +8770,13 @@ static int kvm_pv_clock_pairing(struct kvm_vcpu *vcpu, gpa_t paddr, if (clock_type != KVM_CLOCK_PAIRING_WALLCLOCK) return -KVM_EOPNOTSUPP; + /* + * When tsc is in permanent catchup mode guests won't be able to use + * pvclock_read_retry loop to get consistent view of pvclock + */ + if (vcpu->arch.tsc_always_catchup) + return -KVM_EOPNOTSUPP; + if (!kvm_get_walltime_and_clockread(&ts, &cycle)) return -KVM_EOPNOTSUPP;