[PATCH v24 5/9] arm64: kdump: add kdump support

[Pratyush Anand]

On 22/08/2016:10:29:20 AM, AKASHI Takahiro wrote:
> On Fri, Aug 19, 2016 at 04:52:17PM +0530, Pratyush Anand wrote:
> > On 19/08/2016:10:26:52 AM, AKASHI Takahiro wrote:
> > > >From 740563e4a437f0d6ecf6e421c91433f9b8f19041 Mon Sep 17 00:00:00 2001
> > > From: AKASHI Takahiro <takahiro.akashi at linaro.org>
> > > Date: Fri, 19 Aug 2016 09:57:52 +0900
> > > Subject: [PATCH] arm64: mark reserved memblock regions explicitly
> > > 
> > > ---
> > >  arch/arm64/kernel/setup.c | 9 +++++++--
> > >  1 file changed, 7 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> > > index 38eda13..38589b5 100644
> > > --- a/arch/arm64/kernel/setup.c
> > > +++ b/arch/arm64/kernel/setup.c
> > > @@ -205,10 +205,15 @@ static void __init request_standard_resources(void)
> > >  
> > >  	for_each_memblock(memory, region) {
> > >  		res = alloc_bootmem_low(sizeof(*res));
> > > -		res->name  = "System RAM";
> > > +		if (memblock_is_nomap(region)) {
> > > +			res->name  = "reserved";
> > > +			res->flags = IORESOURCE_MEM | IORESOURCE_BUSY;
> > > +		} else {
> > > +			res->name  = "System RAM";
> > > +			res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
> > > +		}
> > >  		res->start = __pfn_to_phys(memblock_region_memory_base_pfn(region));
> > >  		res->end = __pfn_to_phys(memblock_region_memory_end_pfn(region)) - 1;
> > > -		res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
> > >  
> > >  		request_resource(&iomem_resource, res);
> > 
> > 
> > It will help kexec-tools to prevent copying  of any unnecessary data. I
> > think, then you also need to change phys_offset calculation in kexec-tools. That
> > should be start of either of first "reserved" or "System RAM" block.
> 
> Good point, but I'm not sure this is always true.
> Is there any system whose ACPI memory is *not* part of DRAM
> (so not part of linear mapping)?
> 

Looking into kernel/resource.c:reserve_setup(), it seems that there could be
some none-DRAM area as well, which could be marked as "reserved". So, I think if
we mark nomap region as "reserved" then applications like kexec-tools may not
always identify start of DRAM correctly. Probably, we should give an unique name
to reserved system ram area.

~Pratyush