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xen-devel
Re: [Xen-devel] Re: [PATCH 04/10] xen/mmu: For 1-1 mapping, automaticall
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To: |
Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> |
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Subject: |
Re: [Xen-devel] Re: [PATCH 04/10] xen/mmu: For 1-1 mapping, automatically set _PAGE_IOMAP. |
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From: |
Ian Campbell <Ian.Campbell@xxxxxxxxxx> |
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Date: |
Wed, 22 Dec 2010 16:27:24 +0000 |
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Cc: |
Jeremy Fitzhardinge <jeremy@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>, "hpa@xxxxxxxxx" <hpa@xxxxxxxxx> |
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Wed, 22 Dec 2010 08:28:54 -0800 |
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<20101222150258.GD1760@xxxxxxxxxxxx> |
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<1292967460-15709-1-git-send-email-konrad.wilk@xxxxxxxxxx> <1292967460-15709-5-git-send-email-konrad.wilk@xxxxxxxxxx> <4D112A4B.5000503@xxxxxxxx> <20101222150258.GD1760@xxxxxxxxxxxx> |
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On Wed, 2010-12-22 at 15:02 +0000, Konrad Rzeszutek Wilk wrote:
> On Tue, Dec 21, 2010 at 02:29:31PM -0800, Jeremy Fitzhardinge wrote:
> > On 12/21/2010 01:37 PM, Konrad Rzeszutek Wilk wrote:
> > > @@ -832,6 +832,9 @@ static pteval_t pte_pfn_to_mfn(pteval_t val)
> > > pteval_t flags = val & PTE_FLAGS_MASK;
> > > unsigned long mfn = pfn_to_mfn(pfn);
> > >
> > > + if (mfn == pfn)
> > > + flags |= _PAGE_IOMAP;
> >
> > Why? Does it really make sense to set _PAGE_IOMAP if they just happen
> > to be the same value?
>
> Yes. Without this, user applications, such as 'dmidecode' cannot get
> data.
I think Jeremy's point is that the "mfn == pfn" here has false
positives, since it is possible that a normal RAM page has identical mfn
and pfn by pure chance.
Ian.
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