linux-kernel - Re: __virt_addr_valid vs virtual percpu areas

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Message-ID: <49AF135A.4060604@goop.org>
Date:	Wed, 04 Mar 2009 15:48:42 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Jiri Slaby <jirislaby@...il.com>
CC:	Tejun Heo <htejun@...il.com>, Ingo Molnar <mingo@...e.hu>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Vegard Nossum <vegard.nossum@...il.com>
Subject: Re: __virt_addr_valid vs virtual percpu areas

Jiri Slaby wrote:
> It's not (in the meaning of virt_* functions), but while booting we 
> don't have variables used in VMALLOC_START and VMALLOC_END ready for 
> use on i386.
>
> Maybe we can introduce more clever method/state which would say: hey, 
> vmalloc framework is up and running. And use instead (system_state != 
> SYSTEM_BOOTING) hack.

Yeah, I pieced that together.  I'm just testing a patch with a specific 
__vmalloc_start_set flag to test.

>> This is biting me because I need to translate percpu addresses
>> to pfns, but I only bother doing the full pagetable walk if
>> virt_addr_valid() is false (otherwise I just use __pa()).
>
> Do you need to bother also with vmalloc space?

percpu data gets mapped into the vmalloc region now (when using 4k page 
mappings, at least).

>> Removing this test doesn't seem to harm anything at first glance. Is
>> this OK to do in general (and can we quietly set fire to system_state
>> while we're about it)?
>
> I wouldn't do that, since vmalloc addr is not virt addr, again in the 
> meaning of virt_* functions. And the function wouldn't do the right 
> thing, at least in the RUNNING state anymore.

OK.

    J
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