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SubjectRe: [PATCH v3 2/4] PM: hibernate: make direct map manipulations more explicit
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On 01.11.20 18:08, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
>
> 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@linux.ibm.com>
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
> 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@redhat.com>

--
Thanks,

David / dhildenb

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