Re: [PATCH 0/4] KVM: selftests: Fix and clean up emulator_error_test

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On Mon, Oct 3, 2022 at 4:31 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> On Thu, Sep 29, 2022, David Matlack wrote:
> > Miscellaneous fixes and cleanups to emulator_error_test. The reason I
> > started looking at this test is because it fails when TDP is disabled,
> > which pollutes my test results when I am testing a new series for
> > upstream.
>
> This series defeats the (not well documented) purpose of emulator_error_test.  The
> test exists specifically to verify that KVM emulates in response to EPT violations
> when "allow_smaller_maxphyaddr && guest.MAXPHYADDR < host.MAXPHADDR".

I thought that might have been the case before I sent this series, but
I could not (and still can't) find any evidence to support it. The
commit message and comment at the top of the test all indicate this is
a test for KVM_CAP_EXIT_ON_EMULATION_FAILURE. What did I miss?

Either way, I think we want both types of tests.  In v2 how about I split out:

 (1) exit_on_emulation_failure_test.c: Test that emulation failures
exit to userspace when the cap is enabled, i.e. what
emulator_error_test does by the end of this series.
 (2) smaller_maxphyaddr_emulation_test.c: Test the interaction of
allow_smaller_maxphyaddr and instruction emulation. i.e. what
emulator_error_does at the start of this series plus your suggestions.

The main benefit of splitting out (1) is to test
KVM_CAP_EXIT_ON_EMULATION_FAILURE independent of
allow_smaller_maxphyaddr, since allow_smaller_maxphyaddr is not
enabled by default.


>
> That said, the test could use some upgrades:
>
>   1. Verify that a well-emulated instruction takes #PF(RSVD)
>   2. Verify that FLDS takes #PF(RSVD) when EPT is disabled



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