linux-kernel - Re: [PATCH RFC] paravirt_ops: refactor struct paravirt_ops into smaller pv_*

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Date:	Fri, 28 Sep 2007 11:49:06 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Zachary Amsden <zach@...are.com>
CC:	Andi Kleen <ak@...e.de>, Rusty Russell <rusty@...tcorp.com.au>,
	Avi Kivity <avi@...ranet.com>,
	Glauber de Oliveira Costa <glommer@...il.com>,
	Anthony Liguori <anthony@...emonkey.ws>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Virtualization Mailing List <virtualization@...ts.osdl.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH RFC] paravirt_ops: refactor struct paravirt_ops into	smaller
 pv_*_ops

Zachary Amsden wrote:
> On Fri, 2007-09-28 at 11:10 -0700, Jeremy Fitzhardinge wrote:
>   
>> This patch refactors the paravirt_ops structure into groups of
>> functionally related ops:
>>
>> pv_info - random info, rather than function entrypoints
>> pv_init_ops - functions used at boot time (some for module_init too)
>> pv_misc_ops - lazy mode, which didn't fit well anywhere else
>> pv_time_ops - time-related functions
>> pv_cpu_ops - various privileged instruction ops
>> pv_irq_ops - operations for managing interrupt state
>> pv_apic_ops - APIC operations
>> pv_mmu_ops - operations for managing pagetables
>>
>> There are several motivations for this:
>>
>> 1. Some of these ops will be general to all x86, and some will be
>>    i386/x86-64 specific.  This makes it easier to share common stuff
>>    while allowing separate implementations where needed.
>>
>> 2. At the moment we must export all of paravirt_ops, but modules only
>>    need selected parts of it.  This allows us to export on a case by case
>>    basis (and also choose which export license we want to apply).
>>     
>
> We shouldn't need to export pv_init_ops.  

No.  The only ones I export are:

EXPORT_SYMBOL_GPL(pv_time_ops);
EXPORT_SYMBOL_GPL(pv_cpu_ops);
EXPORT_SYMBOL_GPL(pv_mmu_ops);
EXPORT_SYMBOL_GPL(pv_apic_ops);
EXPORT_SYMBOL    (pv_irq_ops);


> It is debatable whether
> CR2/CR3 should be part of CPU or MMU ops.

Yeah, I was in two minds.  CR3, at least, should be grouped with the
other tlb operations, wherever they go.  And while they're privileged
CPU instructions (cpu_ops), they're more logically related to the rest
of the mmu state.  On the other hand, we could have an ops structure
specifically dedicated to pagetable manipulations, and put the cr3/tlb
ops elsewhere.

>   Also, can we drop write_cr2?
> It isn't used anywhere, so the only reason to keep it is symmetry.
> Which was a fine argument when it was an inline, but now it just adds
> unused junk to the code.
>   

I think its used in some cpu state save/restore code, but its not
relevant to pv-ops.

    J
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