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Subject: Re: [PATCH v4 2/4] PM: hibernate: make direct map manipulations more
 explicit
To: Mike Rapoport <rppt@kernel.org>, Andrew Morton <akpm@linux-foundation.org>
References: <20201103162057.22916-1-rppt@kernel.org>
 <20201103162057.22916-3-rppt@kernel.org>
From: Vlastimil Babka <vbabka@suse.cz>
Message-ID: <9a0780b4-35f8-0ded-c473-d8ab4a26ade5@suse.cz>
Date: Wed, 4 Nov 2020 18:40:28 +0100
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Cc: "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
 David Hildenbrand <david@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
 Dave Hansen <dave.hansen@linux.intel.com>, linux-mm@kvack.org,
 Paul Mackerras <paulus@samba.org>, Pavel Machek <pavel@ucw.cz>,
 "H. Peter Anvin" <hpa@zytor.com>, sparclinux@vger.kernel.org,
 Christoph Lameter <cl@linux.com>, Will Deacon <will@kernel.org>,
 linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, x86@kernel.org,
 Mike Rapoport <rppt@linux.ibm.com>,
 Christian Borntraeger <borntraeger@de.ibm.com>, Ingo Molnar <mingo@redhat.com>,
 Catalin Marinas <catalin.marinas@arm.com>, Len Brown <len.brown@intel.com>,
 Albert Ou <aou@eecs.berkeley.edu>, Vasily Gorbik <gor@linux.ibm.com>,
 linux-pm@vger.kernel.org, Heiko Carstens <hca@linux.ibm.com>,
 David Rientjes <rientjes@google.com>, Borislav Petkov <bp@alien8.de>,
 Andy Lutomirski <luto@kernel.org>, Paul Walmsley <paul.walmsley@sifive.com>,
 "Kirill A. Shutemov" <kirill@shutemov.name>,
 Thomas Gleixner <tglx@linutronix.de>, linux-arm-kernel@lists.infradead.org,
 "Rafael J. Wysocki" <rjw@rjwysocki.net>, linux-kernel@vger.kernel.org,
 Pekka Enberg <penberg@kernel.org>, Palmer Dabbelt <palmer@dabbelt.com>,
 Joonsoo Kim <iamjoonsoo.kim@lge.com>, "Edgecombe,
 Rick P" <rick.p.edgecombe@intel.com>, linuxppc-dev@lists.ozlabs.org,
 "David S. Miller" <davem@davemloft.net>,
 "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org
Sender: "Linuxppc-dev"
 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

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);
>   	}
>   }
>   
>