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kvm: x86: Defer setting of CR2 until #PF delivery 

When exception payloads are enabled by userspace (which is not yet
possible) and a #PF is raised in L2, defer the setting of CR2 until
the #PF is delivered. This allows the L1 hypervisor to intercept the
fault before CR2 is modified.

For backwards compatibility, when exception payloads are not enabled
by userspace, kvm_multiple_exception modifies CR2 when the #PF
exception is raised.

Reported-by: Jim Mattson <jmattson@google.com>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Jim Mattson 2018-10-16 14:29:22 -07:00 committed by Paolo Bonzini
parent 91e86d225e
commit da998b46d2
4 changed files with 62 additions and 21 deletions
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13
arch/x86/kvm/svm.c
View File

@ -805,6 +805,8 @@ static void svm_queue_exception(struct kvm_vcpu *vcpu)
nested_svm_check_exception(svm, nr, has_error_code, error_code))
return;
kvm_deliver_exception_payload(&svm->vcpu);
if (nr == BP_VECTOR && !static_cpu_has(X86_FEATURE_NRIPS)) {
unsigned long rip, old_rip = kvm_rip_read(&svm->vcpu);
@ -2965,16 +2967,13 @@ static int nested_svm_check_exception(struct vcpu_svm *svm, unsigned nr,
svm->vmcb->control.exit_info_1 = error_code;
/*
* FIXME: we should not write CR2 when L1 intercepts an L2 #PF exception.
* The fix is to add the ancillary datum (CR2 or DR6) to structs
* kvm_queued_exception and kvm_vcpu_events, so that CR2 and DR6 can be
* written only when inject_pending_event runs (DR6 would written here
* too). This should be conditional on a new capability---if the
* capability is disabled, kvm_multiple_exception would write the
* ancillary information to CR2 or DR6, for backwards ABI-compatibility.
* EXITINFO2 is undefined for all exception intercepts other
* than #PF.
*/
if (svm->vcpu.arch.exception.nested_apf)
svm->vmcb->control.exit_info_2 = svm->vcpu.arch.apf.nested_apf_token;
else if (svm->vcpu.arch.exception.has_payload)
svm->vmcb->control.exit_info_2 = svm->vcpu.arch.exception.payload;
else
svm->vmcb->control.exit_info_2 = svm->vcpu.arch.cr2;

19
arch/x86/kvm/vmx.c
View File

@ -3292,27 +3292,24 @@ static int nested_vmx_check_exception(struct kvm_vcpu *vcpu, unsigned long *exit
{
struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
unsigned int nr = vcpu->arch.exception.nr;
bool has_payload = vcpu->arch.exception.has_payload;
unsigned long payload = vcpu->arch.exception.payload;
if (nr == PF_VECTOR) {
if (vcpu->arch.exception.nested_apf) {
*exit_qual = vcpu->arch.apf.nested_apf_token;
return 1;
}
/*
* FIXME: we must not write CR2 when L1 intercepts an L2 #PF exception.
* The fix is to add the ancillary datum (CR2 or DR6) to structs
* kvm_queued_exception and kvm_vcpu_events, so that CR2 and DR6
* can be written only when inject_pending_event runs. This should be
* conditional on a new capability---if the capability is disabled,
* kvm_multiple_exception would write the ancillary information to
* CR2 or DR6, for backwards ABI-compatibility.
*/
if (nested_vmx_is_page_fault_vmexit(vmcs12,
vcpu->arch.exception.error_code)) {
*exit_qual = vcpu->arch.cr2;
*exit_qual = has_payload ? payload : vcpu->arch.cr2;
return 1;
}
} else {
/*
* FIXME: we must not write DR6 when L1 intercepts an
* L2 #DB exception.
*/
if (vmcs12->exception_bitmap & (1u << nr)) {
if (nr == DB_VECTOR) {
*exit_qual = vcpu->arch.dr6;
@ -3349,6 +3346,8 @@ static void vmx_queue_exception(struct kvm_vcpu *vcpu)
u32 error_code = vcpu->arch.exception.error_code;
u32 intr_info = nr | INTR_INFO_VALID_MASK;
kvm_deliver_exception_payload(vcpu);
if (has_error_code) {
vmcs_write32(VM_ENTRY_EXCEPTION_ERROR_CODE, error_code);
intr_info |= INTR_INFO_DELIVER_CODE_MASK;

49
arch/x86/kvm/x86.c
View File

@ -400,6 +400,26 @@ static int exception_type(int vector)
return EXCPT_FAULT;
}
void kvm_deliver_exception_payload(struct kvm_vcpu *vcpu)
{
unsigned nr = vcpu->arch.exception.nr;
bool has_payload = vcpu->arch.exception.has_payload;
unsigned long payload = vcpu->arch.exception.payload;
if (!has_payload)
return;
switch (nr) {
case PF_VECTOR:
vcpu->arch.cr2 = payload;
break;
}
vcpu->arch.exception.has_payload = false;
vcpu->arch.exception.payload = 0;
}
EXPORT_SYMBOL_GPL(kvm_deliver_exception_payload);
static void kvm_multiple_exception(struct kvm_vcpu *vcpu,
unsigned nr, bool has_error, u32 error_code,
bool has_payload, unsigned long payload, bool reinject)
@ -441,6 +461,18 @@ static void kvm_multiple_exception(struct kvm_vcpu *vcpu,
vcpu->arch.exception.error_code = error_code;
vcpu->arch.exception.has_payload = has_payload;
vcpu->arch.exception.payload = payload;
/*
* In guest mode, payload delivery should be deferred,
* so that the L1 hypervisor can intercept #PF before
* CR2 is modified. However, for ABI compatibility
* with KVM_GET_VCPU_EVENTS and KVM_SET_VCPU_EVENTS,
* we can't delay payload delivery unless userspace
* has enabled this functionality via the per-VM
* capability, KVM_CAP_EXCEPTION_PAYLOAD.
*/
if (!vcpu->kvm->arch.exception_payload_enabled ||
!is_guest_mode(vcpu))
kvm_deliver_exception_payload(vcpu);
return;
}
@ -486,6 +518,13 @@ void kvm_requeue_exception(struct kvm_vcpu *vcpu, unsigned nr)
}
EXPORT_SYMBOL_GPL(kvm_requeue_exception);
static void kvm_queue_exception_e_p(struct kvm_vcpu *vcpu, unsigned nr,
u32 error_code, unsigned long payload)
{
kvm_multiple_exception(vcpu, nr, true, error_code,
true, payload, false);
}
int kvm_complete_insn_gp(struct kvm_vcpu *vcpu, int err)
{
if (err)
@ -502,11 +541,13 @@ void kvm_inject_page_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault)
++vcpu->stat.pf_guest;
vcpu->arch.exception.nested_apf =
is_guest_mode(vcpu) && fault->async_page_fault;
if (vcpu->arch.exception.nested_apf)
if (vcpu->arch.exception.nested_apf) {
vcpu->arch.apf.nested_apf_token = fault->address;
else
vcpu->arch.cr2 = fault->address;
kvm_queue_exception_e(vcpu, PF_VECTOR, fault->error_code);
kvm_queue_exception_e(vcpu, PF_VECTOR, fault->error_code);
} else {
kvm_queue_exception_e_p(vcpu, PF_VECTOR, fault->error_code,
fault->address);
}
}
EXPORT_SYMBOL_GPL(kvm_inject_page_fault);

2
arch/x86/kvm/x86.h
View File

@ -266,6 +266,8 @@ int kvm_write_guest_virt_system(struct kvm_vcpu *vcpu,
int handle_ud(struct kvm_vcpu *vcpu);
void kvm_deliver_exception_payload(struct kvm_vcpu *vcpu);
void kvm_vcpu_mtrr_init(struct kvm_vcpu *vcpu);
u8 kvm_mtrr_get_guest_memory_type(struct kvm_vcpu *vcpu, gfn_t gfn);
bool kvm_mtrr_valid(struct kvm_vcpu *vcpu, u32 msr, u64 data);