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    SubjectRe: [PATCH v4 2/4] PM: hibernate: make direct map manipulations more explicit
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    On 11/3/20 5:20 PM, 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 pr_warn() 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>
    > Reviewed-by: David Hildenbrand <david@redhat.com>
    > Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

    Acked-by: Vlastimil Babka <vbabka@suse.cz>

    The bool param is a bit more acceptable here, being a private API. But if
    debug_pagealloc_map_pages() becomes split, then it might be easier to split this
    one too...

    > ---
    > include/linux/mm.h | 12 ------------
    > kernel/power/snapshot.c | 32 ++++++++++++++++++++++++++++++--
    > 2 files changed, 30 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..57d54b9d84bb 100644
    > --- a/kernel/power/snapshot.c
    > +++ b/kernel/power/snapshot.c
    > @@ -76,6 +76,34 @@ 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 a warning 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 (ret) {
    > + pr_warn_once("Failed to remap page\n");
    > + return;
    > + }
    > +
    > + flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
    > + } else {
    > + debug_pagealloc_map_pages(page, 1, enable);
    > + }
    > +}
    > +
    > static int swsusp_page_is_free(struct page *);
    > static void swsusp_set_page_forbidden(struct page *);
    > static void swsusp_unset_page_forbidden(struct page *);
    > @@ -1355,9 +1383,9 @@ static void safe_copy_page(void *dst, struct page *s_page)
    > if (kernel_page_present(s_page)) {
    > do_copy_page(dst, page_address(s_page));
    > } else {
    > - kernel_map_pages(s_page, 1, 1);
    > + hibernate_map_page(s_page, 1);
    > do_copy_page(dst, page_address(s_page));
    > - kernel_map_pages(s_page, 1, 0);
    > + hibernate_map_page(s_page, 0);
    > }
    > }
    >
    >

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