KVM: VMX: Extend VMXs #AC interceptor to handle split lock #AC in guest

Two types of #AC can be generated in Intel CPUs:
 1. legacy alignment check #AC
 2. split lock #AC

Reflect #AC back into the guest if the guest has legacy alignment checks
enabled or if split lock detection is disabled.

If the #AC is not a legacy one and split lock detection is enabled, then
invoke handle_guest_split_lock() which will either warn and disable split
lock detection for this task or force SIGBUS on it.

[ tglx: Switch it to handle_guest_split_lock() and rename the misnamed
  helper function. ]

Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lkml.kernel.org/r/20200410115517.176308876@linutronix.de

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 8959514..8305097 100644 (file)
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4588,6 +4588,26 @@ static int handle_machine_check(struct kvm_vcpu *vcpu)
        return 1;
 }
 
+/*
+ * If the host has split lock detection disabled, then #AC is
+ * unconditionally injected into the guest, which is the pre split lock
+ * detection behaviour.
+ *
+ * If the host has split lock detection enabled then #AC is
+ * only injected into the guest when:
+ *  - Guest CPL == 3 (user mode)
+ *  - Guest has #AC detection enabled in CR0
+ *  - Guest EFLAGS has AC bit set
+ */
+static inline bool guest_inject_ac(struct kvm_vcpu *vcpu)
+{
+       if (!boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT))
+               return true;
+
+       return vmx_get_cpl(vcpu) == 3 && kvm_read_cr0_bits(vcpu, X86_CR0_AM) &&
+              (kvm_get_rflags(vcpu) & X86_EFLAGS_AC);
+}
+
 static int handle_exception_nmi(struct kvm_vcpu *vcpu)
 {
        struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -4653,9 +4673,6 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
                return handle_rmode_exception(vcpu, ex_no, error_code);
 
        switch (ex_no) {
-       case AC_VECTOR:
-               kvm_queue_exception_e(vcpu, AC_VECTOR, error_code);
-               return 1;
        case DB_VECTOR:
                dr6 = vmcs_readl(EXIT_QUALIFICATION);
                if (!(vcpu->guest_debug &
@@ -4684,6 +4701,20 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
                kvm_run->debug.arch.pc = vmcs_readl(GUEST_CS_BASE) + rip;
                kvm_run->debug.arch.exception = ex_no;
                break;
+       case AC_VECTOR:
+               if (guest_inject_ac(vcpu)) {
+                       kvm_queue_exception_e(vcpu, AC_VECTOR, error_code);
+                       return 1;
+               }
+
+               /*
+                * Handle split lock. Depending on detection mode this will
+                * either warn and disable split lock detection for this
+                * task or force SIGBUS on it.
+                */
+               if (handle_guest_split_lock(kvm_rip_read(vcpu)))
+                       return 1;
+               fallthrough;
        default:
                kvm_run->exit_reason = KVM_EXIT_EXCEPTION;
                kvm_run->ex.exception = ex_no;