nSVM: interception checks on emulation (was: [PATCH] KVM: nSVM: Fix IOIO size reported on emulation)

Jan Kiszka
2014-06-30T09:27:53Z

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On 2014-06-30 11:07, Jan Kiszka wrote:
> I'm seeing one more issue now: on emulation of "in (%dx),%eax", we leave
> to user space several times and check interception also several times

Correction: we only leave once for user space.

> after returning. We use dx to calculate the port number for the
> interception check. But at some point, user space (QEMU) decides to
> update that register during vmport access - and now we check the wrong
> port in the bitmap (namely port 0). Ideas?
>
> In general, the same interception checks are done multiple times. Once
> after the exit, then again during emulation. Can't we avoid this somehow?
>

OK, we have different interception stages, but it seems we take multiple
ones when we should only take a single:

qemu-system-x86-4455 [000] 38083.617545: kvm_exit: reason EXIT_IOIO rip 0x7fc6ead774e4 info 56580241 7fc6ead774e5
qemu-system-x86-4455 [000] 38083.617547: kvm_nested_vmexit: rip 7fc6ead774e4 reason EXIT_IOIO info1 56580241 info2 7fc6ead774e5 int_info 0 int_info_err 0
qemu-system-x86-4455 [000] 38083.617548: bprint: nested_svm_intercept: 5658 4 3c00bacb 0 1 f
qemu-system-x86-4455 [000] 38083.617549: bprint: nested_svm_intercept: f0
qemu-system-x86-4455 [000] 38083.617553: kvm_emulate_insn: 0:7fc6ead774e4: ed
qemu-system-x86-4455 [000] 38083.617555: bprint: svm_check_intercept: 5658 2 4 43
qemu-system-x86-4455 [000] 38083.617556: bprint: nested_svm_intercept: 5658 4 3c00bacb 0 1 f
qemu-system-x86-4455 [000] 38083.617556: bprint: nested_svm_intercept: f0
qemu-system-x86-4455 [000] 38083.617559: kvm_userspace_exit: reason KVM_EXIT_IO (2)
qemu-system-x86-4455 [000] 38083.617567: bprint: kvm_arch_vcpu_ioctl_get_regs: 5658
qemu-system-x86-4455 [000] 38083.617598: bprint: kvm_arch_vcpu_ioctl_set_regs: 0
qemu-system-x86-4455 [000] 38083.617628: bprint: svm_check_intercept: 0 2 4 43
qemu-system-x86-4455 [000] 38083.617629: bprint: nested_svm_intercept: 0 4 3c00b000 0 1 f
qemu-system-x86-4455 [000] 38083.617630: bprint: nested_svm_intercept: ff
qemu-system-x86-4455 [000] 38083.617631: kvm_nested_vmexit_inject: reason EXIT_IOIO info1 241 info2 7fc6ead774e4 int_info 0 int_info_err 0

And you can also see the rdx writing of user space here (rdx is printed
in kvm_arch_vcpu_ioctl_*).

Jan