linux-kernel - [PATCH 32/41] KVM: SVM: Ensure timestamp counter monotonicity

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sun,  1 Apr 2007 17:35:29 +0300
From:	Avi Kivity <avi@...ranet.com>
To:	kvm-devel@...ts.sourceforge.net
Cc:	linux-kernel@...r.kernel.org, Avi Kivity <avi@...ranet.com>
Subject: [PATCH 32/41] KVM: SVM: Ensure timestamp counter monotonicity

When a vcpu is migrated from one cpu to another, its timestamp counter
may lose its monotonic property if the host has unsynced timestamp counters.
This can confuse the guest, sometimes to the point of refusing to boot.

As the rdtsc instruction is rather fast on AMD processors (7-10 cycles),
we can simply record the last host tsc when we drop the cpu, and adjust
the vcpu tsc offset when we detect that we've migrated to a different cpu.

Signed-off-by: Avi Kivity <avi@...ranet.com>
---
 drivers/kvm/kvm.h |    1 +
 drivers/kvm/svm.c |   21 +++++++++++++++++----
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
index f5e343c..6d0bd7a 100644
--- a/drivers/kvm/kvm.h
+++ b/drivers/kvm/kvm.h
@@ -244,6 +244,7 @@ struct kvm_vcpu {
 	struct mutex mutex;
 	int   cpu;
 	int   launched;
+	u64 host_tsc;
 	struct kvm_run *run;
 	int interrupt_window_open;
 	unsigned long irq_summary; /* bit vector: 1 per word in irq_pending */
diff --git a/drivers/kvm/svm.c b/drivers/kvm/svm.c
index 0542d33..ca2642f 100644
--- a/drivers/kvm/svm.c
+++ b/drivers/kvm/svm.c
@@ -459,7 +459,6 @@ static void init_vmcb(struct vmcb *vmcb)
 {
 	struct vmcb_control_area *control = &vmcb->control;
 	struct vmcb_save_area *save = &vmcb->save;
-	u64 tsc;
 
 	control->intercept_cr_read = 	INTERCEPT_CR0_MASK |
 					INTERCEPT_CR3_MASK |
@@ -517,8 +516,7 @@ static void init_vmcb(struct vmcb *vmcb)
 
 	control->iopm_base_pa = iopm_base;
 	control->msrpm_base_pa = msrpm_base;
-	rdtscll(tsc);
-	control->tsc_offset = -tsc;
+	control->tsc_offset = 0;
 	control->int_ctl = V_INTR_MASKING_MASK;
 
 	init_seg(&save->es);
@@ -606,11 +604,26 @@ static void svm_free_vcpu(struct kvm_vcpu *vcpu)
 
 static void svm_vcpu_load(struct kvm_vcpu *vcpu)
 {
-	get_cpu();
+	int cpu;
+
+	cpu = get_cpu();
+	if (unlikely(cpu != vcpu->cpu)) {
+		u64 tsc_this, delta;
+
+		/*
+		 * Make sure that the guest sees a monotonically
+		 * increasing TSC.
+		 */
+		rdtscll(tsc_this);
+		delta = vcpu->host_tsc - tsc_this;
+		vcpu->svm->vmcb->control.tsc_offset += delta;
+		vcpu->cpu = cpu;
+	}
 }
 
 static void svm_vcpu_put(struct kvm_vcpu *vcpu)
 {
+	rdtscll(vcpu->host_tsc);
 	put_cpu();
 }
 
-- 
1.5.0.5

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/