x86: kvm: svm: propagate errors from skip_emulated_instruction()

On AMD, kvm_x86_ops->skip_emulated_instruction(vcpu) can, in theory,
fail: in !nrips case we call kvm_emulate_instruction(EMULTYPE_SKIP).
Currently, we only do printk(KERN_DEBUG) when this happens and this
is not ideal. Propagate the error up the stack.

On VMX, skip_emulated_instruction() doesn't fail, we have two call
sites calling it explicitly: handle_exception_nmi() and
handle_task_switch(), we can just ignore the result.

On SVM, we also have two explicit call sites:
svm_queue_exception() and it seems we don't need to do anything there as
we check if RIP was advanced or not. In task_switch_interception(),
however, we are better off not proceeding to kvm_task_switch() in case
skip_emulated_instruction() failed.

Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 74e88e5..707ae7f 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1070,7 +1070,7 @@ struct kvm_x86_ops {
 
        void (*run)(struct kvm_vcpu *vcpu);
        int (*handle_exit)(struct kvm_vcpu *vcpu);
-       void (*skip_emulated_instruction)(struct kvm_vcpu *vcpu);
+       int (*skip_emulated_instruction)(struct kvm_vcpu *vcpu);
        void (*set_interrupt_shadow)(struct kvm_vcpu *vcpu, int mask);
        u32 (*get_interrupt_shadow)(struct kvm_vcpu *vcpu);
        void (*patch_hypercall)(struct kvm_vcpu *vcpu,

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 1819033..1ff786d 100644 (file)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -768,7 +768,7 @@ static void svm_set_interrupt_shadow(struct kvm_vcpu *vcpu, int mask)
 
 }
 
-static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
+static int skip_emulated_instruction(struct kvm_vcpu *vcpu)
 {
        struct vcpu_svm *svm = to_svm(vcpu);
 
@@ -777,18 +777,17 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
                svm->next_rip = svm->vmcb->control.next_rip;
        }
 
-       if (!svm->next_rip) {
-               if (kvm_emulate_instruction(vcpu, EMULTYPE_SKIP) !=
-                               EMULATE_DONE)
-                       printk(KERN_DEBUG "%s: NOP\n", __func__);
-               return;
-       }
+       if (!svm->next_rip)
+               return kvm_emulate_instruction(vcpu, EMULTYPE_SKIP);
+
        if (svm->next_rip - kvm_rip_read(vcpu) > MAX_INST_SIZE)
                printk(KERN_ERR "%s: ip 0x%lx next 0x%llx\n",
                       __func__, kvm_rip_read(vcpu), svm->next_rip);
 
        kvm_rip_write(vcpu, svm->next_rip);
        svm_set_interrupt_shadow(vcpu, 0);
+
+       return EMULATE_DONE;
 }
 
 static void svm_queue_exception(struct kvm_vcpu *vcpu)
@@ -819,7 +818,7 @@ static void svm_queue_exception(struct kvm_vcpu *vcpu)
                 * raises a fault that is not intercepted. Still better than
                 * failing in all cases.
                 */
-               skip_emulated_instruction(&svm->vcpu);
+               (void)skip_emulated_instruction(&svm->vcpu);
                rip = kvm_rip_read(&svm->vcpu);
                svm->int3_rip = rip + svm->vmcb->save.cs.base;
                svm->int3_injected = rip - old_rip;
@@ -3896,20 +3895,25 @@ static int task_switch_interception(struct vcpu_svm *svm)
        if (reason != TASK_SWITCH_GATE ||
            int_type == SVM_EXITINTINFO_TYPE_SOFT ||
            (int_type == SVM_EXITINTINFO_TYPE_EXEPT &&
-            (int_vec == OF_VECTOR || int_vec == BP_VECTOR)))
-               skip_emulated_instruction(&svm->vcpu);
+            (int_vec == OF_VECTOR || int_vec == BP_VECTOR))) {
+               if (skip_emulated_instruction(&svm->vcpu) != EMULATE_DONE)
+                       goto fail;
+       }
 
        if (int_type != SVM_EXITINTINFO_TYPE_SOFT)
                int_vec = -1;
 
        if (kvm_task_switch(&svm->vcpu, tss_selector, int_vec, reason,
-                               has_error_code, error_code) == EMULATE_FAIL) {
-               svm->vcpu.run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
-               svm->vcpu.run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
-               svm->vcpu.run->internal.ndata = 0;
-               return 0;
-       }
+                               has_error_code, error_code) == EMULATE_FAIL)
+               goto fail;
+
        return 1;
+
+fail:
+       svm->vcpu.run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+       svm->vcpu.run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
+       svm->vcpu.run->internal.ndata = 0;
+       return 0;
 }
 
 static int cpuid_interception(struct vcpu_svm *svm)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 42ed3fa..26cf4fe 100644 (file)
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1472,8 +1472,11 @@ static int vmx_rtit_ctl_check(struct kvm_vcpu *vcpu, u64 data)
        return 0;
 }
 
-
-static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
+/*
+ * Returns an int to be compatible with SVM implementation (which can fail).
+ * Do not use directly, use skip_emulated_instruction() instead.
+ */
+static int __skip_emulated_instruction(struct kvm_vcpu *vcpu)
 {
        unsigned long rip;
 
@@ -1483,6 +1486,13 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
 
        /* skipping an emulated instruction also counts */
        vmx_set_interrupt_shadow(vcpu, 0);
+
+       return EMULATE_DONE;
+}
+
+static inline void skip_emulated_instruction(struct kvm_vcpu *vcpu)
+{
+       (void)__skip_emulated_instruction(vcpu);
 }
 
 static void vmx_clear_hlt(struct kvm_vcpu *vcpu)
@@ -7705,7 +7715,7 @@ static struct kvm_x86_ops vmx_x86_ops __ro_after_init = {
 
        .run = vmx_vcpu_run,
        .handle_exit = vmx_handle_exit,
-       .skip_emulated_instruction = skip_emulated_instruction,
+       .skip_emulated_instruction = __skip_emulated_instruction,
        .set_interrupt_shadow = vmx_set_interrupt_shadow,
        .get_interrupt_shadow = vmx_get_interrupt_shadow,
        .patch_hypercall = vmx_patch_hypercall,

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6b81c76..73825ab 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6390,9 +6390,11 @@ static void kvm_vcpu_do_singlestep(struct kvm_vcpu *vcpu, int *r)
 int kvm_skip_emulated_instruction(struct kvm_vcpu *vcpu)
 {
        unsigned long rflags = kvm_x86_ops->get_rflags(vcpu);
-       int r = EMULATE_DONE;
+       int r;
 
-       kvm_x86_ops->skip_emulated_instruction(vcpu);
+       r = kvm_x86_ops->skip_emulated_instruction(vcpu);
+       if (unlikely(r != EMULATE_DONE))
+               return 0;
 
        /*
         * rflags is the old, "raw" value of the flags.  The new value has