linux-kernel - Re: [PATCH] x86: define arch_vm_get_page_prot to set _PAGE_IOMAP on VM

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Message-ID: <4CC1E40F.60708@zytor.com>
Date:	Fri, 22 Oct 2010 12:20:47 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	"Xen-devel@...ts.xensource.com" <Xen-devel@...ts.xensource.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: define arch_vm_get_page_prot to set _PAGE_IOMAP
 on VM_IO vmas

On 10/22/2010 12:06 PM, Jeremy Fitzhardinge wrote:
> 
> Well, if you want to map a normal memory page, you'd use, say,
> pfn_pte(pfn, PAGE_KERNEL) to generate the pte.  The pfn is a
> domain-local pseudo-physical address.  When it ends up in
> xen_make_pte(), it will translate the the pfn into a machine-global mfn
> to generate a pte_t which can be inserted into a pagetable.  (And when
> that pagetable starts being used as such, Xen will validate that the mfn
> is actually one the domain is allowed to address.)
> 
> However, if you're doing an ioremap(), then the mapped address is a
> hardware one.  In that case, we construct the pte with
> pfn_pte(device_pfn, PAGE_KERNEL_IO), which sets the _PAGE_IOMAP flag in
> the pte flags.  When it gets to xen_make_pte(), it sees _PAGE_IOMAP and
> constructs a pte_t containing the literal untranslated device_pfn
> (really an mfn).  (And again, Xen will check that the domain has access
> to that mfn before allowing the mapping to be used.)
> 

When you're doing an ioremap(), then the mapped address is *both* a PFN
and an MFN, right?  So why do your need a flag?  That is the part I
don't get...

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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