linux-kernel - [PATCH 5.10 226/236] KVM: x86: Update vCPUs hv_clock before back to guest when tsc

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Message-Id: <20210913131108.039455298@linuxfoundation.org>
Date:   Mon, 13 Sep 2021 15:15:31 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Zelin Deng <zelin.deng@...ux.alibaba.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.10 226/236] KVM: x86: Update vCPUs hv_clock before back to guest when tsc_offset is adjusted

From: Zelin Deng <zelin.deng@...ux.alibaba.com>

commit d9130a2dfdd4b21736c91b818f87dbc0ccd1e757 upstream.

When MSR_IA32_TSC_ADJUST is written by guest due to TSC ADJUST feature
especially there's a big tsc warp (like a new vCPU is hot-added into VM
which has been up for a long time), tsc_offset is added by a large value
then go back to guest. This causes system time jump as tsc_timestamp is
not adjusted in the meantime and pvclock monotonic character.
To fix this, just notify kvm to update vCPU's guest time before back to
guest.

Cc: stable@...r.kernel.org
Signed-off-by: Zelin Deng <zelin.deng@...ux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Message-Id: <1619576521-81399-2-git-send-email-zelin.deng@...ux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kvm/x86.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3116,6 +3116,10 @@ int kvm_set_msr_common(struct kvm_vcpu *
 			if (!msr_info->host_initiated) {
 				s64 adj = data - vcpu->arch.ia32_tsc_adjust_msr;
 				adjust_tsc_offset_guest(vcpu, adj);
+				/* Before back to guest, tsc_timestamp must be adjusted
+				 * as well, otherwise guest's percpu pvclock time could jump.
+				 */
+				kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
 			}
 			vcpu->arch.ia32_tsc_adjust_msr = data;
 		}