Re: [PATCH v3 2/4] PM: hibernate: make direct map manipulations more explicit

[David Hildenbrand]

On 01.11.20 18:08, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@xxxxxxxxxxxxx>
>
> When DEBUG_PAGEALLOC or ARCH_HAS_SET_DIRECT_MAP is enabled a page may be
> not present in the direct map and has to be explicitly mapped before it
> could be copied.
>
> Introduce hibernate_map_page() that will explicitly use
> set_direct_map_{default,invalid}_noflush() for ARCH_HAS_SET_DIRECT_MAP case
> and debug_pagealloc_map_pages() for DEBUG_PAGEALLOC case.
>
> The remapping of the pages in safe_copy_page() presumes that it only
> changes protection bits in an existing PTE and so it is safe to ignore
> return value of set_direct_map_{default,invalid}_noflush().
>
> Still, add a WARN_ON() so that future changes in set_memory APIs will not
> silently break hibernation.
>
> Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> ---
>   include/linux/mm.h      | 12 ------------
>   kernel/power/snapshot.c | 30 ++++++++++++++++++++++++++++--
>   2 files changed, 28 insertions(+), 14 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 1fc0609056dc..14e397f3752c 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2927,16 +2927,6 @@ static inline bool debug_pagealloc_enabled_static(void)
>   #if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_ARCH_HAS_SET_DIRECT_MAP)
>   extern void __kernel_map_pages(struct page *page, int numpages, int enable);
>   
> -/*
> - * When called in DEBUG_PAGEALLOC context, the call should most likely be
> - * guarded by debug_pagealloc_enabled() or debug_pagealloc_enabled_static()
> - */
> -static inline void
> -kernel_map_pages(struct page *page, int numpages, int enable)
> -{
> -	__kernel_map_pages(page, numpages, enable);
> -}
> -
>   static inline void debug_pagealloc_map_pages(struct page *page,
>   					     int numpages, int enable)
>   {
> @@ -2948,8 +2938,6 @@ static inline void debug_pagealloc_map_pages(struct page *page,
>   extern bool kernel_page_present(struct page *page);
>   #endif	/* CONFIG_HIBERNATION */
>   #else	/* CONFIG_DEBUG_PAGEALLOC || CONFIG_ARCH_HAS_SET_DIRECT_MAP */
> -static inline void
> -kernel_map_pages(struct page *page, int numpages, int enable) {}
>   static inline void debug_pagealloc_map_pages(struct page *page,
>   					     int numpages, int enable) {}
>   #ifdef CONFIG_HIBERNATION
> diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
> index 46b1804c1ddf..054c8cce4236 100644
> --- a/kernel/power/snapshot.c
> +++ b/kernel/power/snapshot.c
> @@ -76,6 +76,32 @@ static inline void hibernate_restore_protect_page(void *page_address) {}
>   static inline void hibernate_restore_unprotect_page(void *page_address) {}
>   #endif /* CONFIG_STRICT_KERNEL_RWX  && CONFIG_ARCH_HAS_SET_MEMORY */
>   
> +static inline void hibernate_map_page(struct page *page, int enable)
> +{
> +	if (IS_ENABLED(CONFIG_ARCH_HAS_SET_DIRECT_MAP)) {
> +		unsigned long addr = (unsigned long)page_address(page);
> +		int ret;
> +
> +		/*
> +		 * This should not fail because remapping a page here means
> +		 * that we only update protection bits in an existing PTE.
> +		 * It is still worth to have WARN_ON() here if something
> +		 * changes and this will no longer be the case.
> +		 */
> +		if (enable)
> +			ret = set_direct_map_default_noflush(page);
> +		else
> +			ret = set_direct_map_invalid_noflush(page);
> +
> +		if (WARN_ON(ret))
> +			return;

People seem to prefer pr_warn() now that production kernels have panic 
on warn enabled. It's weird.

> +
> +		flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
> +	} else {
> +		debug_pagealloc_map_pages(page, 1, enable);

Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>

--
Thanks,

David / dhildenb