linux-kernel - Re: __virt_addr_valid vs virtual percpu areas

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Message-ID: <49AF0C81.7060908@gmail.com>
Date:	Thu, 05 Mar 2009 00:19:29 +0100
From:	Jiri Slaby <jirislaby@...il.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
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

On 4.3.2009 23:57, Jeremy Fitzhardinge wrote:
> On i386, __virt_addr_valid() has the test:
>
> if (system_state != SYSTEM_BOOTING && is_vmalloc_addr((void *) x))
> return false;
>
>
> Why is the vmalloc area a valid virtual address while the system is
> booting?

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.

> 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?

> 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.
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