linux-kernel - Re: [PATCH 5.10 049/101] KVM: selftests: Fix kvm_check

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Date:   Mon, 5 Jul 2021 08:10:47 +0100
From:   Fuad Tabba <tabba@...gle.com>
To:     Pavel Machek <pavel@...x.de>
Cc:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 5.10 049/101] KVM: selftests: Fix kvm_check_cap() assertion

 Hi Pavel,

On Sat, Jul 3, 2021 at 4:21 PM Pavel Machek <pavel@...x.de> wrote:
>
> Hi!
>
> > From: Fuad Tabba <tabba@...gle.com>
> >
> > [ Upstream commit d8ac05ea13d789d5491a5920d70a05659015441d ]
> >
> > KVM_CHECK_EXTENSION ioctl can return any negative value on error,
> > and not necessarily -1. Change the assertion to reflect that.
> >
> > Signed-off-by: Fuad Tabba <tabba@...gle.com>
>
> This is userland code, right?
>
> > +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> > @@ -55,7 +55,7 @@ int kvm_check_cap(long cap)
> >               exit(KSFT_SKIP);
> >
> >       ret = ioctl(kvm_fd, KVM_CHECK_EXTENSION, cap);
> > -     TEST_ASSERT(ret != -1, "KVM_CHECK_EXTENSION IOCTL failed,\n"
> > +     TEST_ASSERT(ret >= 0, "KVM_CHECK_EXTENSION IOCTL failed,\n"
> >               "  rc: %i errno: %i", ret, errno);

There's at least one case that I am aware of that potentially would
return a value other than -1 on error, which is a check for
KVM_CAP_MSI_DEVID (-EINVAL, -22):

https://elixir.bootlin.com/linux/latest/source/arch/arm64/kvm/arm.c#L229

Also, considering that this is test code, it might be good to have the
check be as strict as possible.

Cheers,
/fuad

> And syscalls return -1 on error in userland, not anything else. So
> this should not be needed.
>
> Best regards,
>                                                                 Pavel
> --
> DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany