On 10/12/16 at 02:39pm, Pratyush Anand wrote:
> On Wednesday 12 October 2016 05:56 AM, Baoquan He wrote:
> > > PAGE_OFFSET can be get via vaddr - paddr from elf pt_loads so only
> > > > VMALLOC_BASE and VMEMMAP_BASE is necessary..
> > Well, yes, I was wrong. I wrongly thought of kernel text virtual address
> > when I wrote the reply
> So, if you can get PAGE_OFFSET then, probably you do not need to know
> anything else.
> I think, we can simplify makedumpfile code, where we do not need to depend
> on VMALLOC_START or VMEMMAP_START etc.
> "If we know PAGE_OFFSET, we can read from swapper space. If we can read from
> swapper space, then we can know PA of any kernel VA, whether it is VMALLOC,
> or vmemmap or module or kernel text area."
Check makedumpfile code and re-think about this, it's really like you
said, we can convert VA to PA by swapper_pg_dir or init_level4_pgt. But the
reason why we have to involve VMALLOC_START and VMEMMAP_START is that in
x86_64 direct mapping and kernel text mapping are all linear mapping.
Linear mapping can let us do a very efficient translation from VA to
PA. Especially for page filtering, we need get PA of mm related data.
All of them need convert by swapper_pg_dir or init_level4_pgt, that's
inefficient, imagine the current system usually own many Tera bytes of
So here though we can pick up crash memory regions from elf program
header of vmcore and calculate the PAGE_OFFSET, we still need
VMALLOC_START and VMEMMAP_START.
> In fact, I have cleanup patches for ARM64 , which take above approach and
> get rid of need of VMALLOC_START or VMEMMAP_START etc. I will be sending
> them upstream soon.
> Probably, x86 can take the similar approach.
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