KVM: x86: Whitelist port 0x7e for pre-incrementing %rip

[linux-2.6-block.git] / arch / x86 / kvm / x86.c

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9482cb36b92aca35b49df5d631ff35757cda0fa6..57621313deadc75800ad748f0add2fbfc93cce9c 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6539,6 +6539,12 @@ int kvm_emulate_instruction_from_buffer(struct kvm_vcpu *vcpu,
 }
 EXPORT_SYMBOL_GPL(kvm_emulate_instruction_from_buffer);
 
+static int complete_fast_pio_out_port_0x7e(struct kvm_vcpu *vcpu)
+{
+       vcpu->arch.pio.count = 0;
+       return 1;
+}
+
 static int complete_fast_pio_out(struct kvm_vcpu *vcpu)
 {
        vcpu->arch.pio.count = 0;
@@ -6555,12 +6561,23 @@ static int kvm_fast_pio_out(struct kvm_vcpu *vcpu, int size,
        unsigned long val = kvm_register_read(vcpu, VCPU_REGS_RAX);
        int ret = emulator_pio_out_emulated(&vcpu->arch.emulate_ctxt,
                                            size, port, &val, 1);
+       if (ret)
+               return ret;
 
-       if (!ret) {
+       /*
+        * Workaround userspace that relies on old KVM behavior of %rip being
+        * incremented prior to exiting to userspace to handle "OUT 0x7e".
+        */
+       if (port == 0x7e &&
+           kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_OUT_7E_INC_RIP)) {
+               vcpu->arch.complete_userspace_io =
+                       complete_fast_pio_out_port_0x7e;
+               kvm_skip_emulated_instruction(vcpu);
+       } else {
                vcpu->arch.pio.linear_rip = kvm_get_linear_rip(vcpu);
                vcpu->arch.complete_userspace_io = complete_fast_pio_out;
        }
-       return ret;
+       return 0;
 }
 
 static int complete_fast_pio_in(struct kvm_vcpu *vcpu)