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Date:   Tue, 04 Aug 2020 18:16:30 +0100
From:   Marc Zyngier <maz@kernel.org>
To:     =?UTF-8?Q?Alex_Benn=C3=A9e?= <alex.bennee@linaro.org>
Cc:     kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, kvmarm@lists.cs.columbia.edu,
        christoffer.dall@arm.com
Subject: Re: [PATCH  v1 3/3] kernel/configs: don't include PCI_QUIRKS in KVM
 guest configs
In-Reply-To: <87lfiumnc8.fsf@linaro.org>
References: <20200804124417.27102-1-alex.bennee@linaro.org>
 <20200804124417.27102-4-alex.bennee@linaro.org>
 <f80cfa932a650d8f7e8fc02a1656b4c2@kernel.org> <87r1smmpw5.fsf@linaro.org>
 <b78f8715bbaec8fc728a85d614b00688@kernel.org> <87lfiumnc8.fsf@linaro.org>
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On 2020-08-04 16:40, Alex Bennée wrote:
> Marc Zyngier <maz@kernel.org> writes:
> 
>> On 2020-08-04 15:44, Alex Bennée wrote:
>>> Marc Zyngier <maz@kernel.org> writes:
>>> 
>>>> On 2020-08-04 13:44, Alex Bennée wrote:
>>>>> The VIRTIO_PCI support is an idealised PCI bus, we don't need a 
>>>>> bunch
>>>>> of bloat for real world hardware for a VirtIO guest.
>>>> 
>>>> Who says this guest will only have virtio devices?
>>> 
>>> This is true - although what is the point of kvm_guest.config? We
>>> certainly turn on a whole bunch of virt optimised pathways with
>>> PARAVIRT
>>> and HYPERVISOR_GUEST along with the rest of VirtIO.
>> 
>> Most of which actually qualifies as bloat itself as far as KVM/arm64
>> is concerned...
> 
> So here is the question - does the kernel care about having a blessed
> config for a minimal viable guest? They are certainly used in the cloud
> but I understand the kernel is trying to get away from having a zoo of
> configs. What is the actual point of kvm_guest.config? Just an easy
> enabling for developers?

The cloud vendor I know certainly doesn't provide a "dumbed down"
kernel configuration. What they run is either a distro kernel
or something that fits their environment (which does include
HW PCI devices, and hardly any virtio device).

My take is that this kvm-special config isn't that useful in
the real world, and I don't believe there is such thing as a
"minimal viable guest" config, certainly not across architectures
and VMMs. Hopefully it fits someone's development workflow, but
that's probably it.

          M.
-- 
Jazz is not dead. It just smells funny...