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    SubjectRe: [PATCH v3 2/4] PM: hibernate: make direct map manipulations more explicit
    On Mon, Nov 02, 2020 at 10:19:36AM +0100, David Hildenbrand wrote:
    > 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.

    Weird indeed as the whole point of WARN to yell without causing a
    crash...
    I can change to pr_warn though...

    > > +
    > > + flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
    > > + } else {
    > > + debug_pagealloc_map_pages(page, 1, enable);
    >
    > Reviewed-by: David Hildenbrand <david@redhat.com>

    Thanks!

    > --
    > Thanks,
    >
    > David / dhildenb
    >

    --
    Sincerely yours,
    Mike.

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