From: Sean Christopherson <seanjc@google.com>
To: Maxim Levitsky <mlevitsk@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH] KVM: x86: disable on 32-bit unless CONFIG_BROKEN
Date: Wed, 28 Sep 2022 17:55:17 +0000 [thread overview]
Message-ID: <YzSKhUEg3L1eMKOR@google.com> (raw)
In-Reply-To: <ad97d0671774a873175c71c6435763a33569f669.camel@redhat.com>
On Wed, Sep 28, 2022, Maxim Levitsky wrote:
> On Wed, 2022-09-28 at 16:12 +0000, Sean Christopherson wrote:
> > On Wed, Sep 28, 2022, Paolo Bonzini wrote:
> > > 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.
> >
> > Agreed. I too use 32-bit KVM to validate KVM's handling of 32-bit L1 hypervisors,
> > but the maintenance cost is painfully high.
> >
>
> But is it actually? I test it routinely and it it does work quite well IMHO.
> I don't remember that there were that much breakage lately in this area.
Oh, I didn't mean that it actually requires a lot of attention in terms of bug
fixes, what I meant by "maintenance cost" is the cost of testing that all the
flavors of 32-bit KVM actually work. That can be automated to some extent, but
there's a non-trivial cost to maintaining all that automation.
> 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?
next prev parent reply other threads:[~2022-09-28 17:55 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-26 16:51 [PATCH] KVM: x86: disable on 32-bit unless CONFIG_BROKEN Paolo Bonzini
2022-09-27 17:07 ` Sean Christopherson
2022-09-28 7:10 ` Maxim Levitsky
2022-09-28 9:55 ` Paolo Bonzini
2022-09-28 16:12 ` Sean Christopherson
2022-09-28 17:43 ` Maxim Levitsky
2022-09-28 17:44 ` Maxim Levitsky
2022-09-28 17:55 ` Sean Christopherson [this message]
2022-09-29 13:26 ` Paolo Bonzini
2022-09-29 13:52 ` Maxim Levitsky
2022-09-29 15:07 ` Paolo Bonzini
2023-02-17 19:36 ` Thomas Huth
2023-02-22 22:27 ` Sean Christopherson
2023-02-23 7:01 ` Thomas Huth
2023-02-23 8:33 ` Maxim Levitsky
2023-02-23 22:10 ` Sean Christopherson
2023-02-24 6:28 ` Thomas Huth
2022-09-28 10:04 ` Paolo Bonzini
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