Re: [PATCH] KVM: arm64: Don't eagerly teardown the vgic on init error

[Marc Zyngier <maz@kernel.org>]

On Thu, 24 Oct 2024 17:12:22 +0100,
Mark Brown <broonie@kernel.org> wrote:
> 
> [1  <text/plain; us-ascii (7bit)>]
> On Wed, Oct 09, 2024 at 07:36:03PM +0100, Marc Zyngier wrote:
> > As there is very little ordering in the KVM API, userspace can
> > instanciate a half-baked GIC (missing its memory map, for example)
> > at almost any time.
> 
> The vgic_init selftest has started failing in mainline on multiple
> platforms, with a bisect pointing at this patch which is present there
> as commit df5fd75ee305cb5.  The test reports:
> 
> # selftests: kvm: vgic_init
> # Random seed: 0x6b8b4567
> # Running GIC_v3 tests.
> # ==== Test Assertion Failure ====
> #   lib/kvm_util.c:724: false
> #   pid=1947 tid=1947 errno=5 - Input/output error
> #      1	0x0000000000404edb: __vm_mem_region_delete at kvm_util.c:724 (discriminator 5)
> #      2	0x0000000000405d0b: kvm_vm_free at kvm_util.c:762 (discriminator 12)
> #      3	0x0000000000402d5f: vm_gic_destroy at vgic_init.c:101
> #      4	 (inlined by) test_vcpus_then_vgic at vgic_init.c:368
> #      5	 (inlined by) run_tests at vgic_init.c:720
> #      6	0x0000000000401a6f: main at vgic_init.c:748
> #      7	0x0000ffffa7b37543: ?? ??:0
> #      8	0x0000ffffa7b37617: ?? ??:0
> #      9	0x0000000000401b6f: _start at ??:?
> #   KVM killed/bugged the VM, check the kernel log for clues
> not ok 10 selftests: kvm: vgic_init # exit=254
> 
> which does rather look like a test bug rather than a problem in the
> change itself.

Well, the test tries to do braindead things, and then the test
infrastructure seems surprised that KVM tells it to bugger off...

I can paper over it with this (see below), but frankly, someone who
actually cares about this crap should take a look (and ownership).

	M.

diff --git a/tools/testing/selftests/kvm/aarch64/vgic_init.c b/tools/testing/selftests/kvm/aarch64/vgic_init.c
index b3b5fb0ff0a9..60b076ae85ea 100644
--- a/tools/testing/selftests/kvm/aarch64/vgic_init.c
+++ b/tools/testing/selftests/kvm/aarch64/vgic_init.c
@@ -742,6 +742,8 @@ int main(int ac, char **av)
 	pa_bits = vm_guest_mode_params[VM_MODE_DEFAULT].pa_bits;
 	max_phys_size = 1ULL << pa_bits;
 
+	allow_ioctl_returning_eio = true;
+
 	ret = test_kvm_device(KVM_DEV_TYPE_ARM_VGIC_V3);
 	if (!ret) {
 		pr_info("Running GIC_v3 tests.\n");
diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
index bc7c242480d6..988c68a77ce3 100644
--- a/tools/testing/selftests/kvm/include/kvm_util.h
+++ b/tools/testing/selftests/kvm/include/kvm_util.h
@@ -298,6 +298,8 @@ static __always_inline void static_assert_is_vm(struct kvm_vm *vm) { }
 	kvm_do_ioctl((vm)->fd, cmd, arg);			\
 })
 
+extern bool allow_ioctl_returning_eio;
+
 /*
  * Assert that a VM or vCPU ioctl() succeeded, with extra magic to detect if
  * the ioctl() failed because KVM killed/bugged the VM.  To detect a dead VM,
@@ -313,6 +315,8 @@ do {											\
 	static_assert_is_vm(vm);							\
 											\
 	if (cond)									\
+		break;									\
+	if (errno == EIO && allow_ioctl_returning_eio)					\
 		break;									\
 											\
 	if (errno == EIO &&								\
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index a2b7df5f1d39..d9834421ab12 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -25,6 +25,8 @@ static uint32_t last_guest_seed;
 
 static int vcpu_mmap_sz(void);
 
+bool allow_ioctl_returning_eio = false;
+
 int open_path_or_exit(const char *path, int flags)
 {
 	int fd;

-- 
Without deviation from the norm, progress is not possible.