Re: [PATCH v2 2/2] KVM: selftests: Test that KVM_RUN fails for unresolvable host faults

[Christian Borntraeger <borntraeger@linux.ibm.com>]

Am 22.10.26 um 20:18 schrieb Sean Christopherson:
> On Tue, Oct 20, 2026, Christian Borntraeger wrote:
>> Add a test in which the guest writes to a shmem-backed memslot beyond
>> the end of the file.  KVM_RUN must fail with -EFAULT.
>>
>> On x86 the guest enables interrupts, and on s390 the test sets up
>> pfault, so that KVM could handle the fault with an asynchronous page
>> fault.  If KVM mistakes the error for a fault that needs I/O, the vCPU
>> retries the access forever, and the test fails after a timeout.
>>
>> The test is not built for LoongArch, which handles a failed mapping as
>> an MMIO access.
>>
>> Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
>> ---
>>   tools/testing/selftests/kvm/Makefile.kvm      |   1 +
>>   .../selftests/kvm/faultin_sigbus_test.c       | 169 ++++++++++++++++++
> 
> The "sigbus" part of this is confusing, because there is never actually a sigbus.
> Kinda silly, but maybe faultin_efault_test?

Its Friday, so lets ask the British people and let them vote for Faulty_McFaultFace.c? ;-)
Just kidding, what about async_pf_error_test.c ?


> 
>> +static void arch_enable_async_pf(struct kvm_vm *vm, struct kvm_vcpu *vcpu)
>> +{
> 
> ...
> 
>> +}
>> +#else
>> +/* x86 needs guest interrupts on, see guest_code(); nothing to do elsewhere. */
>> +static void arch_enable_async_pf(struct kvm_vm *vm, struct kvm_vcpu *vcpu)
> 
> Nit, maybe arch_enable_host_async_pf()?  Because x86 has PV async #PFs, where

Can do, I will follow your guidance as you have the x86 view.

>> +
>> +	TEST_ASSERT(!(r == -1 && errno == EINTR),
>> +		    "KVM_RUN did not return within %d seconds: the fault on the SIGBUS page is retried forever",
>> +		    TIMEOUT_SECS);
> 
> Rather than assert on EINTR, what if we have sig_alarm() explicitly TEST_FAIL()?
> That way readers don't have to piece together that the EINTR is coming from the
> alarm, and there's less chance of the test somehow getting a false pass because
> KVM manages to morph the signal into EFAULT.  That would also allow using the

I will have a try. Thanks for the feedback.