linux-kernel - Re: [PATCH] EFI: Do not use __pa() to get the physical address of an ioremapped memory range

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Message-ID: <CANejiEXSvT1hGasoowf1nCc5+EWyXr8PSmfpWDJOT0d_vEiKxA@mail.gmail.com>
Date:	Thu, 15 Sep 2011 09:22:24 +0800
From:	Shaohua Li <shli@...nel.org>
To:	Matt Fleming <matt@...sole-pimps.org>
Cc:	huang ying <huang.ying.caritas@...il.com>,
	Zhang Rui <rui.zhang@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Matthew Garrett <mjg59@...f.ucam.org>, x86@...nel.org
Subject: Re: [PATCH] EFI: Do not use __pa() to get the physical address of an
 ioremapped memory range

2011/9/12 Matt Fleming <matt@...sole-pimps.org>:
> On Fri, 2011-09-02 at 13:12 +0800, huang ying wrote:
>> On Thu, Sep 1, 2011 at 8:28 PM, Matt Fleming <matt@...sole-pimps.org> wrote:
>> >
>> > Hmm.. does anyone know why we ioremap_cache() the memory on
>> > CONFIG_X86_32 instead of ioremap_nocache()? In the case of
>> > EFI_MEMORY_MAPPED_IO the memory really needs to be uncached. Then if
>> > we've ioremap'd the memory we should skip set_memory_uc() altogether,
>> > no?
>>
>> Because whether the mapping should be cached is determined by md->attr
>> instead of md->type.  And besides UC, we may add WC, etc support.
>
> Confused.
>
> The CONFIG_X86_64 version of efi_ioremap() looks like this,
>
> void __iomem *__init efi_ioremap(unsigned long phys_addr, unsigned long size,
>                                 u32 type)
> {
>        unsigned long last_map_pfn;
>
>        if (type == EFI_MEMORY_MAPPED_IO)
>                return ioremap(phys_addr, size);
>
> Which uses md->type to figure out if we should call ioremap(), which on
> x86 is #define'd to ioremap_nocache(). CONFIG_X86_32 doesn't do this,
> but it looks to me like it should.
agree. mapping it wrong and fixing it later makes no sense. we should get
the mapping correct at the first.

> Zhang, I agree that calling __pa() on an ioremap()'d region is bogus,
> but I don't understand why no one is seeing this crash on x86-64. Is it
> something to do with the x86-64 memory map layout such that __pa() works
> on an ioremap()'d address?
x86-64 does identity mapping for larger space (from 0 to the last physical mem
even there is hole). Maybe this is the reason.
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