linux-kernel - Re: [PATCH] KVM: x86: disable on 32-bit unless CONFIG

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Message-ID: <15291c3f-d55c-a206-9261-253a1a33dce1@redhat.com>
Date:   Wed, 28 Sep 2022 11:55:23 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: disable on 32-bit unless CONFIG_BROKEN

On 9/28/22 09:10, Maxim Levitsky wrote:
> I also think that outside KVM developers nobody should be using KVM on 32 bit host.
> 
> However for_developement_  I think that 32 bit KVM support is very useful, as it
> allows to smoke test the support for 32 bit nested hypervisors, which I do once in a while,
> and can even probably be useful to some users (e.g running some legacy stuff in a VM,
> which includes a hypervisor, especially to run really legacy OSes / custom bare metal software,
> using an old hypervisor) - or in other words, 32 bit nested KVM is mostly useless, but
> other 32 bit nested hypervisors can be useful.
> 
> Yes, I can always use an older 32 bit kernel in a guest with KVM support, but as long
> as current kernel works, it is useful to use the same kernel on host and guest.

Yeah, I would use older 32 bit kernels just like I use RHEL4 to test PIT 
reinjection. :)  But really the ultimate solution to this would be to 
improve kvm-unit-tests so that we can compile vmx.c and svm.c for 32-bit.

Paolo