On Tue, Jul 05, 2022 at 04:34:09PM +0100, Catalin Marinas wrote:
> On Tue, Jul 05, 2022 at 06:02:02PM +0300, Mike Rapoport wrote:
> > +void __init remap_crashkernel(void)
> > +{
> > +#ifdef CONFIG_KEXEC_CORE
> > + phys_addr_t start, end, size;
> > + phys_addr_t aligned_start, aligned_end;
> > +
> > + if (can_set_direct_map() || IS_ENABLED(CONFIG_KFENCE))
> > + return;
> > +
> > + if (!crashk_res.end)
> > + return;
> > +
> > + start = crashk_res.start & PAGE_MASK;
> > + end = PAGE_ALIGN(crashk_res.end);
> > +
> > + aligned_start = ALIGN_DOWN(crashk_res.start, PUD_SIZE);
> > + aligned_end = ALIGN(end, PUD_SIZE);
> > +
> > + /* Clear PUDs containing crash kernel memory */
> > + unmap_hotplug_range(__phys_to_virt(aligned_start),
> > + __phys_to_virt(aligned_end), false, NULL);
>
> What I don't understand is what happens if there's valid kernel data
> between aligned_start and crashk_res.start (or the other end of the
> range).
Data shouldn't go anywhere :)
There is
+ /* map area from PUD start to start of crash kernel with large pages */
+ size = start - aligned_start;
+ __create_pgd_mapping(swapper_pg_dir, aligned_start,
+ __phys_to_virt(aligned_start),
+ size, PAGE_KERNEL, early_pgtable_alloc, 0);
and
+ /* map area from end of crash kernel to PUD end with large pages */
+ size = aligned_end - end;
+ __create_pgd_mapping(swapper_pg_dir, end, __phys_to_virt(end),
+ size, PAGE_KERNEL, early_pgtable_alloc, 0);
after the unmap, so after we tear down a part of a linear map we
immediately recreate it, just with a different page size.
This all happens before SMP, so there is no concurrency at that point.
> --
> Catalin
--
Sincerely yours,
Mike.
