[PATCH v2] KVM: VMX: Update instruction length on intercepted BP

Jan Kiszka
2010-02-15T14:53:24Z

We intercept #BP while in guest debugging mode. As VM exits due to
intercepted exceptions do not necessarily come with valid
idt_vectoring, we have to update event_exit_inst_len explicitly in such
cases. At least in the absence of migration, this ensures that
re-injections of #BP will find and use the correct instruction length.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

Changes in v2:
- added comments

arch/x86/kvm/vmx.c | 13 +++++++++++++
1 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index f82b072..14873b9 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2775,6 +2775,12 @@ static int handle_rmode_exception(struct kvm_vcpu *vcpu,
kvm_queue_exception(vcpu, vec);
return 1;
case BP_VECTOR:
+ /*
+ * Update instruction length as we may reinject the exception
+ * from user space while in guest debugging mode.
+ */
+ to_vmx(vcpu)->vcpu.arch.event_exit_inst_len =
+ vmcs_read32(VM_EXIT_INSTRUCTION_LEN);
if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP)
return 0;
/* fall through */
@@ -2897,6 +2903,13 @@ static int handle_exception(struct kvm_vcpu *vcpu)
kvm_run->debug.arch.dr7 = vmcs_readl(GUEST_DR7);
/* fall through */
case BP_VECTOR:
+ /*
+ * Update instruction length as we may reinject #BP from
+ * user space while in guest debugging mode. Reading it for
+ * #DB as well causes no harm, it is not used in that case.
+ */
+ vmx->vcpu.arch.event_exit_inst_len =
+ vmcs_read32(VM_EXIT_INSTRUCTION_LEN);
kvm_run->exit_reason = KVM_EXIT_DEBUG;
kvm_run->debug.arch.pc = vmcs_readl(GUEST_CS_BASE) + rip;
kvm_run->debug.arch.exception = ex_no;