Re: [PATCH 2/3] x86: add guest_late_init hook to hypervisor_x86 structure

From: Ingo Molnar <mingo@kernel.org>
To: Juergen Gross <jgross@suse.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
	kvm@vger.kernel.org, xen-devel@lists.xenproject.org,
	tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com,
	boris.ostrovsky@oracle.com, pbonzini@redhat.com,
	rkrcmar@redhat.com, rjw@rjwysocki.net, len.brown@intel.com,
	pavel@ucw.cz
Subject: Re: [PATCH 2/3] x86: add guest_late_init hook to hypervisor_x86 structure
Date: Wed, 8 Nov 2017 10:58:54 +0100	[thread overview]
Message-ID: <20171108095854.b7gqsc44x4jl7b4b@gmail.com> (raw)
In-Reply-To: <7ee9d814-9845-8145-d30a-9570f7cb43d8@suse.com>

* Juergen Gross <jgross@suse.com> wrote:

> On 08/11/17 10:40, Ingo Molnar wrote:
> > 
> > * Juergen Gross <jgross@suse.com> wrote:
> > 
> >>> Plus add a default empty function (which hypervisors can override). This avoids 
> >>> all the hidden conditions and wrappery.
> >>
> >> Hmm, x86_hyper is just a pointer being NULL on bare metal. So we would
> >> have to add a pre-filled struct with dummy functions and in case a
> >> hypervisor is detected we'd need to copy all non-NULL pointers of the
> >> hypervisor specific struct to the pre-filled one.
> > 
> > Ok, I missed that detail - but yeah, since this is mostly about boot code,
> > where readability is king, I still think it would be an overall improvement.
> > 
> > This is the pattern we are trying to use with x86_platform ops for example, and 
> > doing:
> > 
> >   git grep -w x86_platform arch/x86
> > 
> > gives a pretty clear idea about how it's used - while if it was all within 
> > wrappers it would be a lot more difficult to discover all the callsites.
> > 
> > Admittedly it's not done totally consistently:
> > 
> >  arch/x86/kernel/apic/probe_32.c:        if (x86_platform.apic_post_init)
> >  arch/x86/kernel/apic/probe_64.c:        if (x86_platform.apic_post_init)
> >  arch/x86/kernel/ebda.c: if (!x86_platform.legacy.reserve_bios_regions)
> >  arch/x86/kernel/platform-quirks.c:      if (x86_platform.set_legacy_features)
> >  arch/x86/platform/intel-mid/device_libs/platform_mrfld_rtc.c:   if (!x86_platform.legacy.rtc)
> > 
> > ... but the _idea_ behind it is consistent ;-)
> > 
> >> In case there are no objections I can add a patch to modify the current
> >> way x86_hyper is used to the pre-filled variant.
> > 
> > Yeah, sounds good to me!
> 
> Okay. With you mentioning x86_platform: should I make x86_hyper a member
> of x86_platform (e.g. x86_platform.hyper.) ?
> 
> I think this would fit quite nice.

Yeah, seems like a good idea!

Thanks,

	Ingo