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

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Date:   Mon, 5 Jul 2021 14:00:34 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Fuad Tabba <tabba@...gle.com>, Pavel Machek <pavel@...x.de>
Cc:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH 5.10 049/101] KVM: selftests: Fix kvm_check_cap()
 assertion

On 05/07/21 09:10, Fuad Tabba wrote:
>>>
>>>        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

In userspace that becomes -1, errno == EINVAL.  I probably just misread 
the "ret != -1" as "ret == 0" when applying this patch; it doesn't hurt 
but it is certainly not needed for stable.

Paolo