From: Anton Romanov <romanton@google.com>
Date: Wed, 16 Feb 2022 18:26:54 +0000 (+0000)
Subject: kvm: x86: Disable KVM_HC_CLOCK_PAIRING if tsc is in always catchup mode
X-Git-Tag: v5.16.15~58
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=30e14ba65ef1c82f322780cad1f66b3831549c07;p=thirdparty%2Fkernel%2Fstable.git

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@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>
---

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c6eb3e45e3d80..e8f495b9ae103 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;