linux-kernel - Re: [PATCH] KVM: selftests: fix irqfd

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Message-ID: <87zfbnyvk9.wl-maz@kernel.org>
Date: Mon, 25 Aug 2025 21:51:02 +0100
From: Marc Zyngier <maz@...nel.org>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Sebastian Ott <sebott@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Shuah Khan <shuah@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	kvm@...r.kernel.org,
	kvmarm@...ts.linux.dev,
	linux-kselftest@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: selftests: fix irqfd_test on arm64

On Mon, 25 Aug 2025 20:52:21 +0100,
Sean Christopherson <seanjc@...gle.com> wrote:
> 
> On Mon, Aug 25, 2025, Sebastian Ott wrote:
> > irqfd_test on arm triggers the following assertion:
> > ==== Test Assertion Failure ====
> >   include/kvm_util.h:527: !ret
> >   pid=3643 tid=3643 errno=11 - Resource temporarily unavailable
> >      1  0x00000000004026d7: kvm_irqfd at kvm_util.h:527
> >      2  0x0000000000402083: main at irqfd_test.c:100
> >      3  0x0000ffffa5aab587: ?? ??:0
> >      4  0x0000ffffa5aab65f: ?? ??:0
> >      5  0x000000000040236f: _start at ??:?
> >   KVM_IRQFD failed, rc: -1 errno: 11 (Resource temporarily unavailable)
> > 
> > Fix this by setting up a vgic for the vm.
> > 
> > Signed-off-by: Sebastian Ott <sebott@...hat.com>
> > ---
> > @@ -86,14 +90,30 @@ static void juggle_eventfd_primary(struct kvm_vm *vm, int eventfd)
> >  	kvm_irqfd(vm, GSI_BASE_PRIMARY + 1, eventfd, KVM_IRQFD_FLAG_DEASSIGN);
> >  }
> >  
> > +static struct kvm_vm *test_vm_create(void)
> > +{
> > +#ifdef __aarch64__
> > +	struct kvm_vm *vm;
> > +	struct kvm_vcpu *vcpu;
> > +	int gic_fd;
> > +
> > +	vm = vm_create_with_one_vcpu(&vcpu, NULL);
> > +	gic_fd = vgic_v3_setup(vm, 1, 64);
> > +	__TEST_REQUIRE(gic_fd >= 0, "Failed to create vgic-v3");
> 
> I don't think this test requires v3+, any GIC will do.

There is no such thing as "any GIC". You need to know what is
available, and ask for something that actually exists. So while the
above is wrong on the ground that this doesn't work on v2 or v5, the
selection has to be explicit.

> Is there a sane way to handle vGIC creation in kvm_arch_vm_post_create()?  E.g.
> could we create a v3 GIC when possible, and fall back to v2?  And then provide a
> way for tests to express a hard v3 GIC dependency?

You can ask KVM what's available. Like an actual VMM does. There is no
shortage of examples in the current code base.

And ideally, this should be made an integral part of creating a viable
VM, which the current VM creation hack makes a point in not providing.

	M.

-- 
Jazz isn't dead. It just smells funny.