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Re: [RFC PATCH 1/2] hw/i386: -cpu model,-feature,+feature should enable
From: |
David Edmondson |
Subject: |
Re: [RFC PATCH 1/2] hw/i386: -cpu model,-feature,+feature should enable feature |
Date: |
Wed, 20 Jan 2021 10:17:36 +0000 |
On Wednesday, 2021-01-20 at 10:08:03 GMT, Daniel P. Berrangé wrote:
> On Tue, Jan 19, 2021 at 11:30:52AM -0500, Eduardo Habkost wrote:
>> On Tue, Jan 19, 2021 at 04:27:56PM +0000, David Edmondson wrote:
>> > On Tuesday, 2021-01-19 at 10:20:56 -05, Eduardo Habkost wrote:
>> >
>> > > Hi,
>> > >
>> > > Thanks for the patch. Getting rid of special -feature/+feature
>> > > behavior was in our TODO list for a long time.
>> > >
>> > > On Tue, Jan 19, 2021 at 02:22:06PM +0000, David Edmondson wrote:
>> > >> "Minus" features are applied after "plus" features, so ensure that a
>> > >> later "plus" feature causes an earlier "minus" feature to be removed.
>> > >>
>> > >> This has no effect on the existing "-feature,feature=on" backward
>> > >> compatibility code (which warns and turns the feature off).
>> > >
>> > > If we are changing behavior, why not change behavior of
>> > > "-feature,feature=on" at the same time? This would allow us to
>> > > get rid of plus_features/minus_features completely and just make
>> > > +feature/-feature synonyms to feature=on/feature=off.
>> >
>> > Okay, I'll do that.
>> >
>> > Given that there have been warnings associated with
>> > "-feature,feature=on" for a while, changing that behaviour seems
>> > acceptable.
>> >
>> > Would the same be true for changing "-feature,+feature"? (i.e. what this
>> > patch does) Really: can this just be changed, or does there have to be
>> > some period where the behaviour stays the same with a warning?
>>
>> I actually expected warnings to be triggered when using
>> "-feature,+feature" as well. If we were not generating warnings
>> for that case, it will need more careful evaluation, just to be
>> sure it's safe. Igor, do you remember the details here?
>
> Where are you expecting warnings ? I don't see any when launching QEMU
qemu-system-x86_64 -display none -cpu Westmere,-vmx,+vmx
Warnings because the result of this is "-vmx".
> IMHO just leave the parsing unchanged, deprecate it, and then delete
> the code. We don't need to "improve" usability semantics of something
> that we want to delete anyway.
/me nods.
dme.
--
I just bite it, it's for the look I don't light it.
- [RFC PATCH 0/2] x86 CPU feature +/- fiddling and +kvm-no-defaults, David Edmondson, 2021/01/19
- [RFC PATCH 2/2] target/i386: Add "-cpu +kvm-no-defaults", David Edmondson, 2021/01/19
- [RFC PATCH 1/2] hw/i386: -cpu model, -feature, +feature should enable feature, David Edmondson, 2021/01/19
- Re: [RFC PATCH 1/2] hw/i386: -cpu model,-feature,+feature should enable feature, Eduardo Habkost, 2021/01/19
- Re: [External] : Re: [RFC PATCH 1/2] hw/i386: -cpu model,-feature,+feature should enable feature, David Edmondson, 2021/01/19
- Re: [External] : Re: [RFC PATCH 1/2] hw/i386: -cpu model,-feature,+feature should enable feature, Eduardo Habkost, 2021/01/19
- Re: [External] : Re: [RFC PATCH 1/2] hw/i386: -cpu model,-feature,+feature should enable feature, Igor Mammedov, 2021/01/20
- Re: [RFC PATCH 1/2] hw/i386: -cpu model,-feature,+feature should enable feature, David Edmondson, 2021/01/20
- Re: [External] : Re: [RFC PATCH 1/2] hw/i386: -cpu model,-feature,+feature should enable feature, Daniel P . Berrangé, 2021/01/20
- Re: [RFC PATCH 1/2] hw/i386: -cpu model,-feature,+feature should enable feature,
David Edmondson <=
- Re: [RFC PATCH 1/2] hw/i386: -cpu model,-feature,+feature should enable feature, Eduardo Habkost, 2021/01/20
- Re: [RFC PATCH 1/2] hw/i386: -cpu model,-feature,+feature should enable feature, Igor Mammedov, 2021/01/20
- [PATCH] docs/system: Deprecate `-cpu ...,+feature,-feature` syntax, Eduardo Habkost, 2021/01/20
- Re: [PATCH] docs/system: Deprecate `-cpu ..., +feature, -feature` syntax, David Edmondson, 2021/01/20
- Re: [PATCH] docs/system: Deprecate `-cpu ...,+feature,-feature` syntax, Daniel P . Berrangé, 2021/01/21
- Re: [PATCH] docs/system: Deprecate `-cpu ...,+feature,-feature` syntax, John Snow, 2021/01/26
- Re: [PATCH] docs/system: Deprecate `-cpu ...,+feature,-feature` syntax, Igor Mammedov, 2021/01/21
Re: [RFC PATCH 0/2] x86 CPU feature +/- fiddling and +kvm-no-defaults, Daniel P . Berrangé, 2021/01/19