Re: [kvm-unit-tests PATCH 2/2] arm/run: Fix using qemu-system-aarch64 to run aarch32 tests on aarch64

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On Wed, Mar 09, 2022 at 05:12:05PM +0000, Alexandru Elisei wrote:
> Hi,
> 
> On Wed, Mar 09, 2022 at 05:58:12PM +0100, Andrew Jones wrote:
> > On Wed, Mar 09, 2022 at 04:21:17PM +0000, Alexandru Elisei wrote:
> > > From: Andrew Jones <drjones@xxxxxxxxxx>
> > > 
> > > KVM on arm64 can create 32 bit and 64 bit VMs. kvm-unit-tests tries to
> > > take advantage of this by setting the aarch64=off -cpu option. However,
> > > get_qemu_accelerator() isn't aware that KVM on arm64 can run both types
> > > of VMs and it selects qemu-system-arm instead of qemu-system-aarch64.
> > > This leads to an error in premature_failure() and the test is marked as
> > > skipped:
> > > 
> > > $ ./run_tests.sh selftest-setup
> > > SKIP selftest-setup (qemu-system-arm: -accel kvm: invalid accelerator kvm)
> > > 
> > > Fix this by setting QEMU to the correct qemu binary before calling
> > > get_qemu_accelerator().
> > > 
> > > Signed-off-by: Andrew Jones <drjones@xxxxxxxxxx>
> > > [ Alex E: Added commit message, changed the logic to make it clearer ]
> > > Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
> > > ---
> > >  arm/run | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > > 
> > > diff --git a/arm/run b/arm/run
> > > index 2153bd320751..5fe0a45c4820 100755
> > > --- a/arm/run
> > > +++ b/arm/run
> > > @@ -13,6 +13,11 @@ processor="$PROCESSOR"
> > >  ACCEL=$(get_qemu_accelerator) ||
> > >  	exit $?
> > >  
> > > +# KVM for arm64 can create a VM in either aarch32 or aarch64 modes.
> > > +if [ "$ACCEL" = kvm ] && [ -z "$QEMU" ] && [ "$HOST" = "aarch64" ]; then
> > > +	QEMU=qemu-system-aarch64
> > > +fi
> > > +
> > >  qemu=$(search_qemu_binary) ||
> > >  	exit $?
> > >  
> > > -- 
> > > 2.35.1
> > >
> > 
> > So there's a bug with this patch which was also present in the patch I
> > proposed. By setting $QEMU before we call search_qemu_binary() we may
> > force a "A QEMU binary was not found." failure even though a perfectly
> > good 'qemu-kvm' binary is present.
> 
> I noticed that search_qemu_binary() tries to search for both
> qemu-system-ARCH_NAME and qemu-kvm, and I first thought that qemu-kvm is a
> legacy name for qemu-system-ARCH_NAME.
> 
> I just did some googling, and I think it's actually how certain distros (like
> SLES) package qemu-system-ARCH_NAME, is that correct?

Right

> 
> If that is so, one idea I toyed with (for something else) is to move the error
> messages from search_qemu_binary() to the call sites, that way arm/run can first
> try to find qemu-system-aarch64, then fallback to qemu-kvm, and only after both
> aren't found exit with an error. Just a suggestion, in case you find it useful.

We don't have to move the error messages, even if we want to use
search_qemu_binary() as a silent check. We can just call it with
a &>/dev/null and then check its return code. I still need to
allocate some time to think more about this though.

Thanks,
drew

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