Re: [kvm-unit-tests PATCH v1 0/3] x86: fix async page fault issues

[Sean Christopherson <seanjc@google.com>]

On Tue, Dec 12, 2023, Dan Wu wrote:
> When running asyncpf test, it gets skipped without a clear reason:
> 
>     ./asyncpf
> 
>     enabling apic
>     smp: waiting for 0 APs
>     paging enabled
>     cr0 = 80010011
>     cr3 = 107f000
>     cr4 = 20
>     install handler
>     enable async pf
>     alloc memory
>     start loop
>     end loop
>     start loop
>     end loop
>     SUMMARY: 0 tests
>     SKIP asyncpf (0 tests)
> 
> The reason is that KVM changed to use interrupt-based 'page-ready' notification
> and abandoned #PF-based 'page-ready' notification mechanism. Interrupt-based
> 'page-ready' notification requires KVM_ASYNC_PF_DELIVERY_AS_INT to be set as well
> in MSR_KVM_ASYNC_PF_EN to enable asyncpf.
> 
> This series tries to fix the problem by separating two testcases for different mechanisms.
> 
> - For old #PF-based notification, changes current asyncpf.c to add CPUID check
>   at the beginning. It checks (KVM_FEATURE_ASYNC_PF && !KVM_FEATURE_ASYNC_PF_INT),
>   otherwise it gets skipped.
> 
> - For new interrupt-based notification, add a new test, asyncpf-int.c, to check
>   (KVM_FEATURE_ASYNC_PF && KVM_FEATURE_ASYNC_PF_INT) and implement interrupt-based
>   'page-ready' handler.

Using #PF to deliver page-ready is completely dead, no?  Unless I'm mistaken, let's
just drop the existing support and replace it with the interrupted-based mechanism.
I see no reason to continue maintaining the old crud.  If someone wants to verify
an old, broken KVM, then they can use the old version of KUT.