From: Thomas Huth <thuth@redhat.com>
To: Sean Christopherson <seanjc@google.com>,
Maxim Levitsky <mlevitsk@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
"Daniel P. Berrange" <berrange@redhat.com>
Subject: Re: [PATCH] KVM: x86: disable on 32-bit unless CONFIG_BROKEN
Date: Fri, 24 Feb 2023 07:28:30 +0100 [thread overview]
Message-ID: <1fc187c0-e1b1-bb8c-bee2-0820598a8cd9@redhat.com> (raw)
In-Reply-To: <Y/fkTs5ajFy0hP1U@google.com>
On 23/02/2023 23.10, Sean Christopherson wrote:
> On Thu, Feb 23, 2023, Maxim Levitsky wrote:
>> On Thu, 2023-02-23 at 08:01 +0100, Thomas Huth wrote:
>>> On 22/02/2023 23.27, Sean Christopherson wrote:
>>>> On Fri, Feb 17, 2023, Thomas Huth wrote:
>>>>> On 29/09/2022 15.52, Maxim Levitsky wrote:
>>>>>> 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.
>>>>>
>>>>> FWIW, from the QEMU perspective, it would be very helpful to remove 32-bit
>>>>> KVM support from the kernel. The QEMU project currently struggles badly with
>>>>> keeping everything tested in the CI in a reasonable amount of time. The
>>>>> 32-bit KVM kernel support is the only reason to keep the qemu-system-i386
>>>>> binary around - everything else can be covered with the qemu-system-x86_64
>>>>> binary that is a superset of the -i386 variant (except for the KVM part as
>>>>> far as I know).
>>>>> Sure, we could also drop qemu-system-i386 from the CI without dropping the
>>>>> 32-bit KVM code in the kernel, but I guess things will rather bitrot there
>>>>> even faster in that case, so I'd appreciate if the kernel could drop the
>>>>> 32-bit in the near future, too.
>>>>
>>>> Ya, I would happily drop support for 32-bit kernels today, the only sticking point
>>>> is the lack of 32-bit shadow paging test coverage, which unfortunately is a rather
>>>> large point. :-(
>>>
>>> From your point of view, would it be OK if QEMU dropped qemu-system-i386?
>>> I.e. would it be fine to use older versions of QEMU only for that test
>>> coverage (or do you even use a different userspace for testing that)?
>
> For me personally, I have no objection to dropping qemu-system-i386 support in
> future QEMU releases. I update my 32-bit images very, very infrequently, so I
> probably wouldn't even notice for like 5 years :-)
>
>> From my point of view qemu-system-x86_64 does run 32 bit guests just fine.
>
> Right, but unless I seriously misunderstand what qemu-system-x86_64 ecompasses,
> it can't be used to run guests of 32-bit _hosts_, which is what we need to test
> shadowing of 32-bit NPT.
That's what I've been told in the past, too, and that's why I asked. Thanks
for the clarification!
To summarize: My takeaway is that nobody really needs qemu-system-i386
anymore for recent development - the remaining 32-bit KVM use cases can be
done with older versions of QEMU instead, thus it should be fine for the
QEMU project to drop qemu-system-i386 nowadays.
Thanks,
Thomas
next prev parent reply other threads:[~2023-02-24 6:29 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
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 [this message]
2022-09-28 10:04 ` Paolo Bonzini
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