On Wed, Oct 28, 2020 at 09:15:38PM +0000, Edgecombe, Rick P wrote:
> On Sun, 2020-10-25 at 12:15 +0200, Mike Rapoport wrote:
> > + if (IS_ENABLED(CONFIG_ARCH_HAS_SET_DIRECT_MAP)) {
> > + unsigned long addr = (unsigned
> > long)page_address(page);
> > + int ret;
> > +
> > + if (enable)
> > + ret = set_direct_map_default_noflush(page);
> > + else
> > + ret = set_direct_map_invalid_noflush(page);
> > +
> > + if (WARN_ON(ret))
> > + return;
> > +
> > + flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
> > + } else {
> > + debug_pagealloc_map_pages(page, 1, enable);
> > + }
>
> Looking at the arm side again, I think this might actually introduce a
> regression for the arm/hibernate/DEBUG_PAGEALLOC combo.
>
> Unlike __kernel_map_pages(), it looks like arm's cpa will always bail
> in the set_direct_map_() functions if rodata_full is false.
>
> So if rodata_full was disabled but debug page alloc is on, then this
> would now skip remapping the pages. I guess the significance depends
> on whether hibernate could actually try to save any DEBUG_PAGEALLOC
> unmapped pages. Looks like it to me though.
__kernel_map_pages() on arm64 will also bail out if rodata_full is
false:
void __kernel_map_pages(struct page *page, int numpages, int enable)
{
if (!debug_pagealloc_enabled() && !rodata_full)
return;
set_memory_valid((unsigned long)page_address(page), numpages, enable);
}
So using set_direct_map() to map back pages removed from the direct map
with __kernel_map_pages() seems safe to me.
--
Sincerely yours,
Mike.
