Patch-mainline: v5.17-rc6
Git-commit: 3a55f729240a686aa8af00af436306c0cd532522
References: git-fixes
From: Anton Romanov <romanton@google.com>
Date: Wed, 16 Feb 2022 18:26:54 +0000
Subject: [PATCH] kvm: x86: Disable KVM_HC_CLOCK_PAIRING if tsc is in always
 catchup mode

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: Juergen Gross <jgross@suse.com>
---
 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 b8bd8da32045..3471efe47e5f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8943,6 +8943,13 @@ 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;
 
-- 
2.35.3