linux-kernel - Re: [PATCH 2/4] PM: hibernate: improve robustness of mapping pages in the direct map

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Date:   Wed, 28 Oct 2020 21:15:38 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
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Subject: Re: [PATCH 2/4] PM: hibernate: improve robustness of mapping pages in
 the direct map

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.