Re: [Xen-devel] Physical memory start contraints in the Linux kernel (Was: Re: Xen osstest on Calxeda midway progress (Was: Re: [xen-unstable test] 21486: tolerable FAIL - PUSHED))

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 11/12/2013 03:32 PM, Ian Campbell wrote:
> On Tue, 2013-11-12 at 15:24 +0000, Julien Grall wrote:
> > On 11/12/2013 02:57 PM, Ian Campbell wrote:
> > > On Tue, 2013-11-12 at 14:52 +0000, Julien Grall wrote:
> > > > On 11/12/2013 02:41 PM, Russell King - ARM Linux wrote:
> > > > > On Tue, Nov 12, 2013 at 02:35:10PM +0000, Julien Grall wrote:
> > > > > > During some debugging on the Arndale and Midway, I found another
> > > > > > constraint with CONFIG_ARM_PATCH_PHYS_VIRT.
> > > > > > I have noticed that all the kernel physical addresses must be lower than
> > > > > > the corresponding virtual addresses. So the delta offset compute in
> > > > > > __fixup_pv_table (arch/arm/kernel/head.S) must always be negative.
> > > > > > If this assertion is not validated, when the kernel will browse the
> > > > > > memory bank (sanity_check_info in arch/arm/mm/mmu.c), __phys(...) will
> > > > > > compute a wrong address and will result to consider all memory bank as
> > > > > > highmem.
> > > > > >
> > > > > > After digging in the code, it seems it's due to some optimization during
> > > > > > opcode fixup in __fixup_a_pvtable. Is it a wanted constraint?
> > > > > Are you talking about the code in v3.12 or the code in -next ?
> > > > I was talking about 3.12. I have just checked -next and my issue seems
> > > > to be fixed by the commit f52bb722547f43caeaecbcc62db9f3c3b80ead9b.
> > > > I should have checked earlier, thanks.
> > > Should we revert your Xen side fix^Wworkaround then:
> > For now it's only in -next. I would wait until this commit is at least
> > in Linux master, otherwise we will likely break vanilla/distro kernel
> > for Xen 4.4.
> OK. Can you keep an eye on it and let me know if/when the time comes to
> revert?
No problem.

> Is the fix a candidate for stable? Seems like a bit of a big exciting
> fix for what was an quite recently an obscure corner case...
I think yes, as soon as Linux contains this fix we will be able to 
revert the commit in Xen.
--
Julien Grall

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