On 04/18/16 at 09:36am, Russell King - ARM Linux wrote:
> On Mon, Apr 18, 2016 at 01:38:20PM +0800, Baoquan He wrote:
> > On 04/14/16 at 09:00pm, Russell King wrote:
> > > On PAE systems (eg, ARM LPAE) the vmcore note may be located above
> > > 4GB physical on 32-bit architectures, so we need a wider type than
> > > "unsigned long" here. Arrange for paddr_vmcoreinfo_note() to return
> > > a phys_addr_t, thereby allowing it to be located above 4GB.
> >
> > At first glance, it sounds great. But I can't imagine a scenario where
> > on pae system kernel can be located above 4G. As far as I know i386 and
> > its pae can't do this because the current linux VM implementation can't
> > allow that. I am not familiar with arm system. So please correct me if
> > I was wrong.
>
> You are wrong. That's precisely why this patch exists.
I don't know arm is different then i386. On i386 the kernel text mapping
is linear, just as follow:
#define __phys_addr_nodebug(x) ((x) - PAGE_OFFSET)
But arm seems not linear.
static inline phys_addr_t __virt_to_phys(unsigned long x)
{
phys_addr_t t;
if (sizeof(phys_addr_t) == 4) {
__pv_stub(x, t, "add", __PV_BITS_31_24);
} else {
__pv_stub_mov_hi(t);
__pv_add_carry_stub(x, t);
}
return t;
}
So on arm PAE this change makes sense.
Besides, I checked kexec/arch/arm/kexec-zImage-arm.c and found function
locate_hole() is used to find position for arm kernel.
unsigned long locate_hole(struct kexec_info *info,
unsigned long hole_size, unsigned long hole_align,
unsigned long hole_min, unsigned long hole_max,
int hole_end)
The type unsigned long for hole_max limit the region where arm kernel is
loaded. So withough modifying this I doubt arm PAE can really be loaded
above 4G.
Thanks
Baoquan
>
> --
> RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/
> FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
> according to speedtest.net.
>
> _______________________________________________
> kexec mailing list
> kexec at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec
