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

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Date:	Mon, 12 Sep 2011 15:52:10 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	huang ying <huang.ying.caritas@...il.com>
Cc:	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

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.

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?

-- 
Matt Fleming, Intel Open Source Technology Center

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