2 files changed, 40 insertions, 9 deletions
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index bd57639fd5db..3e03f37f43ea 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -385,6 +385,8 @@ struct kvm_vcpu_arch {
        /* emulate context */
        struct x86_emulate_ctxt emulate_ctxt;
+        bool emulate_regs_need_sync_to_vcpu;
+        bool emulate_regs_need_sync_from_vcpu;
        gpa_t time;
        struct pvclock_vcpu_time_info hv_clock;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1d5a7f418795..3416a3473849 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4420,6 +4420,7 @@ static void init_emulate_ctxt(struct kvm_vcpu *vcpu)
        vcpu->arch.emulate_ctxt.guest_mode = is_guest_mode(vcpu);
        memset(c, 0, sizeof(struct decode_cache));
        memcpy(c->regs, vcpu->arch.regs, sizeof c->regs);
+        vcpu->arch.emulate_regs_need_sync_from_vcpu = false;
 }
 int kvm_inject_realmode_interrupt(struct kvm_vcpu *vcpu, int irq)
@@ -4502,6 +4503,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
 {
        int r;
        struct decode_cache *c = &vcpu->arch.emulate_ctxt.decode;
+        bool writeback = true;
        kvm_clear_exception_queue(vcpu);
        vcpu->arch.mmio_fault_cr2 = cr2;
@@ -4542,9 +4544,12 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
                return EMULATE_DONE;
        }
-        /* this is needed for vmware backdor interface to work since it
+        /* this is needed for vmware backdoor interface to work since it
           changes registers values  during IO operation */
-        memcpy(c->regs, vcpu->arch.regs, sizeof c->regs);
+        if (vcpu->arch.emulate_regs_need_sync_from_vcpu) {
+                vcpu->arch.emulate_regs_need_sync_from_vcpu = false;
+                memcpy(c->regs, vcpu->arch.regs, sizeof c->regs);
+        }
 restart:
        r = x86_emulate_insn(&vcpu->arch.emulate_ctxt);
@@ -4565,19 +4570,28 @@ restart:
        } else if (vcpu->arch.pio.count) {
                if (!vcpu->arch.pio.in)
                        vcpu->arch.pio.count = 0;
+                else
+                        writeback = false;
                r = EMULATE_DO_MMIO;
-        } else if (vcpu->mmio_needed)
+        } else if (vcpu->mmio_needed) {
+                if (!vcpu->mmio_is_write)
+                        writeback = false;
                r = EMULATE_DO_MMIO;
-        else if (r == EMULATION_RESTART)
+        } else if (r == EMULATION_RESTART)
                goto restart;
        else
                r = EMULATE_DONE;
-        toggle_interruptibility(vcpu, vcpu->arch.emulate_ctxt.interruptibility);
+        if (writeback) {
-        kvm_set_rflags(vcpu, vcpu->arch.emulate_ctxt.eflags);
+                toggle_interruptibility(vcpu,
-        kvm_make_request(KVM_REQ_EVENT, vcpu);
+                                vcpu->arch.emulate_ctxt.interruptibility);
-        memcpy(vcpu->arch.regs, c->regs, sizeof c->regs);
+                kvm_set_rflags(vcpu, vcpu->arch.emulate_ctxt.eflags);
-        kvm_rip_write(vcpu, vcpu->arch.emulate_ctxt.eip);
+                kvm_make_request(KVM_REQ_EVENT, vcpu);
+                memcpy(vcpu->arch.regs, c->regs, sizeof c->regs);
+                vcpu->arch.emulate_regs_need_sync_to_vcpu = false;
+                kvm_rip_write(vcpu, vcpu->arch.emulate_ctxt.eip);
+        } else
+                vcpu->arch.emulate_regs_need_sync_to_vcpu = true;
        return r;
 }
@@ -5587,6 +5601,18 @@ out:
 int kvm_arch_vcpu_ioctl_get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
 {
+        if (vcpu->arch.emulate_regs_need_sync_to_vcpu) {
+                /*
+                 * We are here if userspace calls get_regs() in the middle of
+                 * instruction emulation. Registers state needs to be copied
+                 * back from emulation context to vcpu. Usrapace shouldn't do
+                 * that usually, but some bad designed PV devices (vmware
+                 * backdoor interface) need this to work
+                 */
+                struct decode_cache *c = &vcpu->arch.emulate_ctxt.decode;
+                memcpy(vcpu->arch.regs, c->regs, sizeof c->regs);
+                vcpu->arch.emulate_regs_need_sync_to_vcpu = false;
+        }
        regs->rax = kvm_register_read(vcpu, VCPU_REGS_RAX);
        regs->rbx = kvm_register_read(vcpu, VCPU_REGS_RBX);
        regs->rcx = kvm_register_read(vcpu, VCPU_REGS_RCX);
@@ -5614,6 +5640,9 @@ int kvm_arch_vcpu_ioctl_get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
 int kvm_arch_vcpu_ioctl_set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
 {
+        vcpu->arch.emulate_regs_need_sync_from_vcpu = true;
+        vcpu->arch.emulate_regs_need_sync_to_vcpu = false;
        kvm_register_write(vcpu, VCPU_REGS_RAX, regs->rax);
        kvm_register_write(vcpu, VCPU_REGS_RBX, regs->rbx);
        kvm_register_write(vcpu, VCPU_REGS_RCX, regs->rcx);