[PATCH 5.15 057/110] kvm: x86: Disable KVM_HC_CLOCK_PAIRING if tsc is in always catchup mode

Greg Kroah-Hartman
2022-03-14T12:20:33Z

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 8213f7fb71a7..61bc54748f22 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8666,6 +8666,13 @@ 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