linux-kernel - Re: [PATCH v2] ARM: early fixmap support for earlycon

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Date:	Wed, 21 Jan 2015 09:59:10 +0100
From:	Stefan Agner <stefan@...er.ch>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Mark Salter <msalter@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	Laura Abbott <lauraa@...eaurora.org>,
	Arnd Bergmann <arnd@...db.de>, Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v2] ARM: early fixmap support for earlycon

On 2015-01-21 00:48, Russell King - ARM Linux wrote:
> On Wed, Jan 21, 2015 at 12:37:44AM +0100, Stefan Agner wrote:
>> Add early fixmap support, initially to support permanent, fixed
>> mapping support for early console. A temporary, early pte is
>> created which is migrated to a permanent mapping in paging_init.
>> This is also needed since the attributs may change as the memory
>> types are initialized. The 3MiB range of fixmap spans two pte
>> tables, but currently only one pte is created for early fixmap
>> support.
> 
> I think this needs to be done more carefully - I think the entry(ies)
> should be removed, the TLBs flushed, and the new entry established.
> So:

I'm not experienced in mm development, hence please review critical.
 
> 
>> +static void __init early_fixmap_shutdown(void)
>> +{
>> +	int i;
>> +
>> +	pte_offset_fixmap = &pte_offset_late_fixmap;
>> +	pmd_clear(fixmap_pmd(fix_to_virt(__end_of_permanent_fixed_addresses - 1)));
> 
> I think you should flush tlbs here.

Even this shutdown function is still before preemption or SMP, hence
local_flush_tlb_kernel_page should be fine here?

--
Stefan
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