Re: [kvm-unit-tests PATCH v2 0/3] Regression test for L1 LDTR persistence bug

[Jim Mattson <jmattson@google.com>]

On Fri, Oct 15, 2021 at 12:55 PM Jim Mattson <jmattson@google.com> wrote:
>
> In Linux commit afc8de0118be ("KVM: nVMX: Set LDTR to its
> architecturally defined value on nested VM-Exit"), Sean suggested that
> this bug was likely benign, but it turns out that--for us, at
> least--it can result in live migration failures. On restore, we call
> KVM_SET_SREGS before KVM_SET_NESTED_STATE, so when L2 is active at the
> time of save/restore, the target vmcs01 is temporarily populated with
> L2 values. Hence, the LDTR visible to L1 after the next emulated
> VM-exit is L2's, rather than its own.
>
> This issue is significant enough that it warrants a regression
> test. Unfortunately, at the moment, the best we can do is check for
> the LDTR persistence bug. I'd like to be able to trigger a
> save/restore from within the L2 guest, but AFAICT, there's no way to
> do that under qemu. Does anyone want to implement a qemu ISA test
> device that triggers a save/restore when its configured I/O port is
> written to?
>
> Jim Mattson (3):
>   x86: Fix operand size for lldt
>   x86: Make set_gdt_entry usable in 64-bit mode
>   x86: Add a regression test for L1 LDTR persistence bug
>
> v1 -> v2:
>   Reworded report messages at Sean's suggestion.
>
>  lib/x86/desc.c      | 41 +++++++++++++++++++++++++++++++----------
>  lib/x86/desc.h      |  3 ++-
>  lib/x86/processor.h |  2 +-
>  x86/cstart64.S      |  1 +
>  x86/vmx_tests.c     | 39 +++++++++++++++++++++++++++++++++++++++
>  5 files changed, 74 insertions(+), 12 deletions(-)
>
> --
> 2.33.0.1079.g6e70778dc9-goog
>
Ping.