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Re: [RFC PATCH v2 02/22] xen: add CONFIG_XENFV_MACHINE and CONFIG_XEN_EM


From: Paolo Bonzini
Subject: Re: [RFC PATCH v2 02/22] xen: add CONFIG_XENFV_MACHINE and CONFIG_XEN_EMU options for Xen emulation
Date: Tue, 13 Dec 2022 01:39:57 +0100



Il lun 12 dic 2022, 23:23 David Woodhouse <dwmw2@infradead.org> ha scritto:
On Mon, 2022-12-12 at 18:07 +0100, Paolo Bonzini wrote:
> On 12/9/22 10:55, David Woodhouse wrote:
> >   config KVM
> >       bool
> > +    imply XEN_EMU if (I386 || X86_64)
>
> No need for the "imply", just make it "default y" below and it will have
> the same effect.
>
> >
> > diff --git a/target/Kconfig b/target/Kconfig
> > index 83da0bd293..e19c9d77b5 100644
> > --- a/target/Kconfig
> > +++ b/target/Kconfig
> > @@ -18,3 +18,7 @@ source sh4/Kconfig
> >  source sparc/Kconfig
> >  source tricore/Kconfig
> >  source xtensa/Kconfig
> > +
> > +config XEN_EMU
> > +    bool
> > +    depends on KVM && (I386 || X86_64)
>
> Please place it in hw/xen/Kconfig.

Perhaps I misunderstand, but I'm not sure that is consistent with what
Philippe was asking for in 
d203e13d-e2f9-5816-030d-c1449bde364d@linaro.org/" rel="noreferrer noreferrer" target="_blank">https://lore.kernel.org/qemu-devel/d203e13d-e2f9-5816-030d-c1449bde364d@linaro.org/
specifically:

>> I rather have hw/ and target/ features disentangled, so I'd use
>> CONFIG_XEN_EMU under target/ and CONFIG_XENFV_MACHINE under hw/,
>> eventually having CONFIG_XEN_EMU depending on CONFIG_XENFV_MACHINE
>> and -- for now -- CONFIG_KVM.

However the dependency of the xenfv machine is misguided. In principle there is no reason to depend on KVM as opposed to TCG, too, which is why I didn't suggest hw/i386/kvm for either the devices or the Kconfig file.

The idea there seems to be that XEN_EMU is a *target* feature since it
covers the support in target/i386/kvm.

But yes, it *also* covers the devices I'm adding to hw/i386/kvm. Do I
want a *separate* config symbol for that? Or just make those depend on
XENFV_MACHINE && XEN_EMU ?

I'll move XEN_EMU to hw/i386/Kconfig for now, thereby doing what
*neither* of you said (I don't think hw/xen/Kconfig is the best choice
when the *code* it enables is under hw/i386/kvm?)

Yeah there is no especially better match. I guess hw/i386 is fine, since there will be code in mc->kvm_type. It would be either there or in target/i386/Kconfig, but not target/Kconfig.

Paolo 

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