On Tue, Feb 16, 2010 at 09:05:40AM +0100, Jan Kiszka wrote: > Gleb Natapov wrote: > > On Mon, Feb 15, 2010 at 03:53:04PM +0100, Jan Kiszka wrote: > >> 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. > >> > > Thinking about it some more. Why do we exit to userspace at all if we > > intercept wrong #DB? It seams to me not wise to have ability to inject > > exceptions from userspace. Exceptions generation mechanism is a part of > > CPU and we shouldn't outsource part of CPU functionality to userspace. > > The guest debugging API was design to avoid maintaining a "countless" > number of breakpoints in kernel space and instead chose to loop over > user space to decide about #DB & #BP. So this part is required even if > we start thinking about an alternative interface in the future. > How much is "countless"? 10000? I am sure we can handle this. > Jan > > > > >> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> > >> --- > >> > >> 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; > > > > -- > > Gleb. > -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
