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SubjectRe: [PATCH] ARM: fix bug which lowmem size is limited to 760MB
On Tue, 8 Sep 2015, Russell King - ARM Linux wrote:

> On Mon, Sep 07, 2015 at 03:40:36PM -0400, Nicolas Pitre wrote:
> > On Mon, 7 Sep 2015, Arnd Bergmann wrote:
> >
> > > On Thursday 03 September 2015 21:24:00 Nicolas Pitre wrote:
> > > > If 768MB targets were common place then it could be worth changing the
> > > > default vmalloc size to accommodate this memory size and testing all the
> > > > other targets to make sure no regressions are introduced. But given it
> > > > is easy to change the default via the kernel cmdline, and that you lose
> > > > only 8 MB otherwise, I don't think it is worth the trouble and/or the
> > > > risk.
> > >
> > > Agreed.
> >
> > Well... I think there is a better solution.
>
> Doesn't this clash with things like:
>
> #define UNCACHEABLE_ADDR 0xff000000 /* IRQ_STAT */
>
> ?

It looks like the move might actually "fix" it. That UNCACHEABLE_ADDR
is mapped with:

static struct map_desc ebsa110_io_desc[] __initdata = {
/*
* sparse external-decode ISAIO space
*/
{ /* IRQ_STAT/IRQ_MCLR */
.virtual = (unsigned long)IRQ_STAT,
.pfn = __phys_to_pfn(TRICK4_PHYS),
.length = TRICK4_SIZE,
.type = MT_DEVICE
},
[...]
};

This is passed to iotable_init(), then to create_mapping(). There you
have:

if ((md->type == MT_DEVICE || md->type == MT_ROM) &&
md->virtual >= PAGE_OFFSET &&
(md->virtual < VMALLOC_START || md->virtual >= VMALLOC_END)) {
pr_warn("BUG: mapping for 0x%08llx at 0x%08lx out of vmalloc space\n",
(long long)__pfn_to_phys((u64)md->pfn), md->virtual);
}

So you must have hit the above warning somehow. Incidentally, this
IRQ_STAT entry is the only one that happened to be outside the vmalloc
area. By moving VMALLOC_END from 0xff000000 to 0xff800000 the warning
will be gone.


Nicolas


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