On 2011-04-12 20:31, Serge E. Hallyn wrote: > Quoting Jan Kiszka (jan.kiszka@xxxxxxxxxxx): >> On 2011-04-12 16:16, Avi Kivity wrote: >>> On 04/12/2011 05:12 PM, Serge E. Hallyn wrote: >>>> Quoting Avi Kivity (avi@xxxxxxxxxx): >>>>> On 04/12/2011 10:53 AM, Serge E. Hallyn wrote: >>>>> >Quoting Avi Kivity (avi@xxxxxxxxxx): >>>>> >> On 04/09/2011 12:09 AM, Serge E. Hallyn wrote: >>>>> >> >Hi, >>>>> >> > >>>>> >> >at https://bugs.launchpad.net/ubuntu/+source/qemu-kvm/+bug/747090, it was >>>>> >> >found that emulate_int_real() sometimes pushes the wrong eip when doing a >>>>> >> >int. Whereas with non-kvm qemu we push the next instruction after the >>>>> >> >int, with kvm we push the addr of the instruction itself. >>>>> >> > >>>>> >> >>>>> >> >>>>> >> The code says: >>>>> >> >>>>> >> c->src.val = c->eip; >>>>> >> emulate_push(ctxt, ops); >>>>> >> rc = writeback(ctxt, ops); >>>>> >> if (rc != X86EMUL_CONTINUE) >>>>> >> return rc; >>>>> >> >>>>> >> which appears to be the address of the next instruction from my >>>>> >> reading of the code (see how insn_fetch() increments c->eip). >>>>> > >>>>> >Nevertheless removing commits >>>>> > >>>>> > a92601bb707f6f49fd5563ef3d09928e70cc222e >>>>> > 63995653ade16deacaea5b49ceaf6376314593ac >>>>> > 6e154e56b4d7a6a28c54f0984e13d3f8defc4755 >>>>> > >>>>> >changes the eip value being pushed. If you look at >>>>> >a92601bb707f6f49fd5563ef3d09928e70cc222e, you see: >>>>> > >>>>> > if (vmx->rmode.vm86_active) { >>>>> >- vmx->rmode.irq.pending = true; >>>>> >- vmx->rmode.irq.vector = nr; >>>>> >- vmx->rmode.irq.rip = kvm_rip_read(vcpu); >>>>> >- if (kvm_exception_is_soft(nr)) >>>>> >- vmx->rmode.irq.rip += >>>>> >- vmx->vcpu.arch.event_exit_inst_len; >>>>> >- intr_info |= INTR_TYPE_SOFT_INTR; >>>>> >- vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, intr_info); >>>>> >- vmcs_write32(VM_ENTRY_INSTRUCTION_LEN, 1); >>>>> >- kvm_rip_write(vcpu, vmx->rmode.irq.rip - 1); >>>>> >+ if (kvm_inject_realmode_interrupt(vcpu, nr) != EMULATE_DONE) >>>>> >+ kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu); >>>>> > return; >>>>> > } >>>>> > >>>>> >but kvm_inject_realmode_interrupt() does not appear to increment >>>>> >vmx->rmode.irq.rip anywhere, as the code being replaced does. >>>>> >>>>> Ah, I see now. There are two cases, hard interrupt and soft >>>>> interrupts. I guess hard interrupts are handled fine, and the >>>>> failing case is >>>>> >>>>> guest executes INTn instruction in guest mode >>>>> vmx intercepts a page fault (say due to access to the IDT or the stack) >>>>> kvm notes that a soft interrupt was in progress (vmx_complete_interrupts) >>>>> kvm handles the exception >>>>> reinject the interrupt while reentering the guest >>>>> >>>>> so we do need something like >>>>> >>>>> if (soft) >>>>> vcpu->arch.emulate_ctxt.eip += inst_len; >>>>> >>>>> in kvm_inject_realmode_interrupt(). >>>> >>>> Oops, right. Disregard last email pls :) >>>> >>>> So is 'kvm_exception_is_soft(irq)' a reliable check? >>>> >>> >>> No, need to check vcpu->arch.interrupt.soft instead. Not sure about >>> kvm_exception_is_soft(). Jan? >> >> Jumping late on this, I don't understand the question. Reliable /wrt what? > > As to whether we are supposed to increment eip or not. From a brief refresh-reading, I would say if (interrupt.soft || kvm_exception_is_soft(nr)) increment_eip_by_inst_len but only for those interrupts/exceptions which were raised by the triggering instructions, _not_ for exceptions raise while processing them (e.g. a page fault while accessing the IDT). Jan
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