[RFC 05/26] KVM: x86: Reset hardware history at vCPU's sched_in/out

[Zhao Liu]

From: Zhao Liu <zhao1.liu@xxxxxxxxx>

Reset the classification history of the vCPU thread when it's scheduled
in and scheduled out. Hardware will start the classification of the vCPU
thread from scratch.

This helps protect Host/VM history information from leaking Host history
to VMs or leaking VM history to sibling VMs.

Tested-by: Yanting Jiang <yanting.jiang@xxxxxxxxx>
Signed-off-by: Zhao Liu <zhao1.liu@xxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h | 2 --
 arch/x86/kvm/x86.c              | 8 ++++++++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 2be78549bec8..b5b2d0fde579 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -2280,8 +2280,6 @@ static inline int kvm_cpu_get_apicid(int mps_cpu)
 
 int memslot_rmap_alloc(struct kvm_memory_slot *slot, unsigned long npages);
 
-static inline void kvm_arch_sched_out(struct kvm_vcpu *vcpu) {}
-
 #define KVM_CLOCK_VALID_FLAGS						\
 	(KVM_CLOCK_TSC_STABLE | KVM_CLOCK_REALTIME | KVM_CLOCK_HOST_TSC)
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 363b1c080205..cd9a7251c768 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -79,6 +79,7 @@
 #include <asm/div64.h>
 #include <asm/irq_remapping.h>
 #include <asm/mshyperv.h>
+#include <asm/hreset.h>
 #include <asm/hypervisor.h>
 #include <asm/tlbflush.h>
 #include <asm/intel_pt.h>
@@ -12491,9 +12492,16 @@ void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu)
 		pmu->need_cleanup = true;
 		kvm_make_request(KVM_REQ_PMU, vcpu);
 	}
+
+	reset_hardware_history();
 	static_call(kvm_x86_sched_in)(vcpu, cpu);
 }
 
+void kvm_arch_sched_out(struct kvm_vcpu *vcpu)
+{
+	reset_hardware_history();
+}
+
 void kvm_arch_free_vm(struct kvm *kvm)
 {
 #if IS_ENABLED(CONFIG_HYPERV)
-- 
2.34.1