Patch-mainline: v5.15-rc1

Git-commit: d9130a2dfdd4b21736c91b818f87dbc0ccd1e757

References: git-fixes

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

Date: Wed, 28 Apr 2021 10:22:01 +0800

Subject: [PATCH] KVM: x86: Update vCPU's hv_clock before back to guest when

 tsc_offset is adjusted

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@vger.kernel.org

Signed-off-by: Zelin Deng <zelin.deng@linux.alibaba.com>

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Message-Id: <1619576521-81399-2-git-send-email-zelin.deng@linux.alibaba.com>

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Signed-off-by: Juergen Gross <jgross@suse.com>

---

 arch/x86/kvm/x86.c | 4 ++++

 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c

index 1a00af1b076b..28ef14155726 100644

--- a/arch/x86/kvm/x86.c

+++ b/arch/x86/kvm/x86.c

@@ -3321,6 +3321,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)

 			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;

 		}

-- 

2.35.3