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

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Message-ID: <b8fa9561295bb6af2b7fcaa8125c6a3b89b305c7.camel@redhat.com>
Date:   Thu, 29 Sep 2022 16:52:26 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Paolo Bonzini <pbonzini@...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 Thu, 2022-09-29 at 15:26 +0200, Paolo Bonzini wrote:
> On 9/28/22 19:55, Sean Christopherson wrote:
> > > As far as my opinion goes I do volunteer to test this code more often,
> > > and I do not want to see the 32 bit KVM support be removed*yet*.
> > 
> > Yeah, I 100% agree that it shouldn't be removed until we have equivalent test
> > coverage.  But I do think it should an "off-by-default" sort of thing.  Maybe
> > BROKEN is the wrong dependency though?  E.g. would EXPERT be a better option?
> 
> Yeah, maybe EXPERT is better but I'm not sure of the equivalent test 
> coverage.  32-bit VMX/SVM kvm-unit-tests are surely a good idea, but 
> what's wrong with booting an older guest?

>From my point of view, using the same kernel source for host and the guest
is easier because you know that both kernels behave the same.

About EXPERT, IMHO these days most distros already dropped 32 bit suport thus anyway
one needs to compile a recent 32 bit kernel manually - thus IMHO whoever
these days compiles a 32 bit kernel, knows what they are doing.

I personally would wait few more releases when there is a pressing reason to remove
this support.

AFAIK, it is not really possible to remove most of the legacy direct mmu
because shadowing mmu still can use it (I think Sean told me that once).

Best regards,
	Maxim Levitsky

> 
> Paolo
>