linux-kernel - [PATCH 5.16 065/121] kvm: x86: Disable KVM_HC_CLOCK

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Date:   Mon, 14 Mar 2022 12:54:08 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Anton Romanov <romanton@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.16 065/121] kvm: x86: Disable KVM_HC_CLOCK_PAIRING if tsc is in always catchup mode

From: Anton Romanov <romanton@...gle.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@...gle.com>
Message-Id: <20220216182653.506850-1-romanton@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.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