On 2/16/22 19:26, Anton Romanov wrote:
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>
---
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 7131d735b1ef..d0b31b115922 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8945,6 +8945,13 @@ static int kvm_pv_clock_pairing(struct kvm_vcpu *vcpu, gpa_t paddr,
if (!kvm_get_walltime_and_clockread(&ts, &cycle))
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_EFAULT;
+
KVM_EFAULT is for invalid addresses. I changed it back to EOPNOTSUPP
and queued the patch.
Paolo
