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xen-devel
[Xen-devel] Re: [PATCH 6/8] xen/debug: WARN_ON when 1-1 but no _PAGE_IOM
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To: |
Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> |
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Subject: |
[Xen-devel] Re: [PATCH 6/8] xen/debug: WARN_ON when 1-1 but no _PAGE_IOMAP flag set. |
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From: |
Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx> |
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Date: |
Tue, 4 Jan 2011 19:20:56 +0000 |
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Cc: |
Jeremy Fitzhardinge <jeremy@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>, "hpa@xxxxxxxxx" <hpa@xxxxxxxxx> |
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Tue, 04 Jan 2011 11:22:29 -0800 |
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<20110104184604.GB1505@xxxxxxxxxxxx> |
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Citrix Systems, Inc. |
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References: |
<1293738517-7287-1-git-send-email-konrad.wilk@xxxxxxxxxx> <1293738517-7287-7-git-send-email-konrad.wilk@xxxxxxxxxx> <1294161878.3831.654.camel@xxxxxxxxxxxxxxxxxxxxxx> <20110104184604.GB1505@xxxxxxxxxxxx> |
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On Tue, 2011-01-04 at 18:46 +0000, Konrad Rzeszutek Wilk wrote:
> On Tue, Jan 04, 2011 at 05:24:38PM +0000, Ian Campbell wrote:
> > On Thu, 2010-12-30 at 19:48 +0000, Konrad Rzeszutek Wilk wrote:
> > > Only enabled if XEN_DEBUG_FS is enabled.
> >
> > Bit of an odd configuration option to use. Perhaps co-opt
> > CONFIG_PARAVIRT_DEBUG instead?
> >
> > Or maybe we need a new XEN_DEBUG option? or just make it a developer
> > only EXTRA_CFLAGS +=-DDEBUG thing?
>
> I think the 'XEN_DEBUG' works better.
> >
> > Is this only temporary until the need for _PAGE_IOMAP is removed anyway?
>
> I was thinking to leave it as a way to weed out bugs, but I could as well
> just leave it in my "debug" branch and not propose it upstream.
>
> I am not sure how to remove the _PAGE_IOMAP fully. We need some _flag_ to
> signal 'xen_pte_val' that the PTE should not be looked up in the M2P.
>
> Otherwise, for identity mappings, the value is 0xfffff.. (or 0x55555..
> sometimes)
> and the PTE ends up being messed up. Instead there is a check to see if
> _PAGE_IOMAP is part of the PTE, and if so, no M2P lookup is done.
>
> I guess we could do the M2P irregardless and just see if it is 0xfffff... and
> if so just return the PTE without any changes.
Perhaps this ties in with the m2p overlay which Stefano+Jeremy have been
working on to deal with granted foreign pages? I/O pages are a bit like
foreign memory (if you squint enough)...
Ian.
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