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

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Date:	Thu, 15 Sep 2011 09:52:15 +0800
From:	Zhang Rui <rui.zhang@...el.com>
To:	Shaohua Li <shli@...nel.org>
Cc:	Matt Fleming <matt@...sole-pimps.org>,
	huang ying <huang.ying.caritas@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH] EFI: Do not use __pa() to get the physical address of
 an ioremapped memory range

On Thu, 2011-09-15 at 09:22 +0800, Shaohua Li wrote:
> 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.
> 
So what kinds of memory regions need ioremap_nocache?
should we make this decision based on the memory range type or attribute
or even both of them?

-rui

> > 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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