linux-kernel - Re: [PATCH v2 25/25] KVM: selftests: Add fred exception tests

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Date: Wed, 24 Apr 2024 09:08:18 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Muhammad Usama Anjum <usama.anjum@...labora.com>
Cc: Xin Li <xin3.li@...el.com>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
	linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	pbonzini@...hat.com, corbet@....net, tglx@...utronix.de, mingo@...hat.com, 
	bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com, 
	shuah@...nel.org, vkuznets@...hat.com, peterz@...radead.org, 
	ravi.v.shankar@...el.com, xin@...or.com
Subject: Re: [PATCH v2 25/25] KVM: selftests: Add fred exception tests

On Sat, Mar 30, 2024, Muhammad Usama Anjum wrote:
> On 2/7/24 10:26 PM, Xin Li wrote:
> > Add tests for FRED event data and VMX nested-exception.
> > 
> > FRED is designed to save a complete event context in its stack frame,
> > e.g., FRED saves the faulting linear address of a #PF into a 64-bit
> > event data field defined in FRED stack frame.  As such, FRED VMX adds
> > event data handling during VMX transitions.
> > 
> > Besides, FRED introduces event stack levels to dispatch an event handler
> > onto a stack baesd on current stack level and stack levels defined in
> > IA32_FRED_STKLVLS MSR for each exception vector.  VMX nested-exception
> > support ensures a correct event stack level is chosen when a VM entry
> > injects a nested exception, which is regarded as occurred in ring 0.
> > 
> > To fully test the underlying FRED VMX code, this test should be run one
> > more round with EPT disabled to inject page faults as nested exceptions.
> > 
> > Originally-by: Shan Kang <shan.kang@...el.com>
> > Signed-off-by: Xin Li <xin3.li@...el.com>
> Thank you for the new test patch. We have been trying to ensure TAP
> conformance for tests which cannot be achieved if new tests aren't using
> TAP already.

Who is "we"?

> Please make your test TAP compliant.

This isn't entirely reasonable feedback.  I'm all for getting KVM selftests
TAP-friendly, but the current reality is that the KVM selftests infrastructure
doesn't make it easy to be TAP compliant.  We're working on improving things,
i.e. I do hope/want to get to a state where it's a hard requirement for KVM
selftests to be TAP compliant, but we aren't there yet.

If you have specific feedback on _how_ to make a test TAP compliant, then by all
means provide that feedback.  But a drive-by "make your test TAP compliant" isn't
super helpful.

> > ---
> >  tools/testing/selftests/kvm/Makefile          |   1 +
> >  .../selftests/kvm/include/x86_64/processor.h  |  32 ++
> >  .../testing/selftests/kvm/x86_64/fred_test.c  | 297 ++++++++++++++++++
> Add generated binary object to .gitignore.

This should be unnecessary (though I haven't actually verified by building), as
KVM selftests ignore most everything by default since commit 43e96957e8b8
("KVM: selftests: Use pattern matching in .gitignore").