linux-kernel - Re: [PATCH 2/3] x86: add guest_late_init hook to hypervisor

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Date:   Wed, 8 Nov 2017 10:40:13 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Juergen Gross <jgross@...e.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org,
        xen-devel@...ts.xenproject.org, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com, boris.ostrovsky@...cle.com,
        pbonzini@...hat.com, rkrcmar@...hat.com, rjw@...ysocki.net,
        len.brown@...el.com, pavel@....cz
Subject: Re: [PATCH 2/3] x86: add guest_late_init hook to hypervisor_x86
 structure


* Juergen Gross <jgross@...e.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!

Thanks,

	Ingo