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Subject[PATCH v4 2/7] x86: kvm: svm: propagate errors from skip_emulated_instruction()
Date
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>
---
arch/x86/include/asm/kvm_host.h | 2 +-
arch/x86/kvm/svm.c | 36 ++++++++++++++++++---------------
arch/x86/kvm/vmx/vmx.c | 16 ++++++++++++---
arch/x86/kvm/x86.c | 6 ++++--
4 files changed, 38 insertions(+), 22 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 7b0a4ee77313..f9e6d0b0f581 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1068,7 +1068,7 @@ 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 7e843b340490..8299b0de06e2 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -770,7 +770,7 @@ 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);

@@ -779,18 +779,17 @@ 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)
@@ -821,7 +820,7 @@ 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;
@@ -3899,20 +3898,25 @@ 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 074385c86c09..358827b5bc44 100644
--- 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)
@@ -7700,7 +7710,7 @@ 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 c6d951cbd76c..e8f797fe9d9e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6383,9 +6383,11 @@ 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
--
2.20.1
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