Re: [PATCH v3] KVM: x86/xen: Implement hvm_op/HVMOP_flush_tlbs hypercall

[Sean Christopherson <seanjc@google.com>]

On Tue, Apr 18, 2023, Metin Kaya wrote:
> Implement in-KVM support for Xen's HVMOP_flush_tlbs hypercall, which
> allows the guest to flush all vCPU's TLBs. KVM doesn't provide an
> ioctl() to precisely flush guest TLBs, and punting to userspace would
> likely negate the performance benefits of avoiding a TLB shootdown in
> the guest.
> 
> Signed-off-by: Metin Kaya <metikaya@amazon.co.uk>
> 
> ---
> v3:
>   - Addressed comments for v2.
>   - Verified with XTF/invlpg test case.
> 
> v2:
>   - Removed an irrelevant URL from commit message.
> ---
>  arch/x86/kvm/xen.c                 | 15 +++++++++++++++
>  include/xen/interface/hvm/hvm_op.h |  3 +++
>  2 files changed, 18 insertions(+)

I still don't see a testcase.

  : This doesn't even compile.  I'll give you one guess as to how much confidence I
  : have that this was properly tested.
  : 
  : Aha!  And QEMU appears to have Xen emulation support.  That means KVM-Unit-Tests
  : is an option.  Specifically, extend the "access" test to use this hypercall instead
  : of INVLPG.  That'll verify that the flush is actually being performed as expteced.

Let me be more explicit this time: I am not applying this without a test.  I don't
care how trivial a patch may seem, I'm done taking patches without test coverage
unless there's a *really* good reason for me to do so.