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    Subject[PATCH 5.16 065/121] kvm: x86: Disable KVM_HC_CLOCK_PAIRING if tsc is in always catchup mode
    Date
    From: Anton Romanov <romanton@google.com>

    [ 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@google.com>
    Message-Id: <20220216182653.506850-1-romanton@google.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/x86/kvm/x86.c | 7 +++++++
    1 file changed, 7 insertions(+)

    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;

    --
    2.34.1


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