On 3/9/2020 8:22 PM, gregkh@xxxxxxxxxxxxxxxxxxx wrote: > > This is a note to let you know that I've just added the patch titled > > mm, hotplug: fix page online with DEBUG_PAGEALLOC compiled but not enabled > > to the 5.4-stable tree which can be found at: > http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary > > The filename of the patch is: > mm-hotplug-fix-page-online-with-debug_pagealloc-compiled-but-not-enabled.patch > and it can be found in the queue-5.4 subdirectory. > > If you, or anyone else, feels it should not be added to the stable tree, > please let <stable@xxxxxxxxxxxxxxx> know about it. > > > From c87cbc1f007c4b46165f05ceca04e1973cda0b9c Mon Sep 17 00:00:00 2001 > From: Vlastimil Babka <vbabka@xxxxxxx> > Date: Thu, 5 Mar 2020 22:28:42 -0800 > Subject: mm, hotplug: fix page online with DEBUG_PAGEALLOC compiled but not enabled > > From: Vlastimil Babka <vbabka@xxxxxxx> > > commit c87cbc1f007c4b46165f05ceca04e1973cda0b9c upstream. > > Commit cd02cf1aceea ("mm/hotplug: fix an imbalance with DEBUG_PAGEALLOC") > fixed memory hotplug with debug_pagealloc enabled, where onlining a page > goes through page freeing, which removes the direct mapping. Some arches > don't like when the page is not mapped in the first place, so > generic_online_page() maps it first. This is somewhat wasteful, but > better than special casing page freeing fast paths. > > The commit however missed that DEBUG_PAGEALLOC configured doesn't mean > it's actually enabled. One has to test debug_pagealloc_enabled() since > 031bc5743f15 ("mm/debug-pagealloc: make debug-pagealloc boottime > configurable"), or alternatively debug_pagealloc_enabled_static() since > 8e57f8acbbd1 ("mm, debug_pagealloc: don't rely on static keys too early"), > but this is not done. > > As a result, a s390 kernel with DEBUG_PAGEALLOC configured but not enabled > will crash: > > Unable to handle kernel pointer dereference in virtual kernel address space > Failing address: 0000000000000000 TEID: 0000000000000483 > Fault in home space mode while using kernel ASCE. > AS:0000001ece13400b R2:000003fff7fd000b R3:000003fff7fcc007 S:000003fff7fd7000 P:000000000000013d > Oops: 0004 ilc:2 [#1] SMP > CPU: 1 PID: 26015 Comm: chmem Kdump: loaded Tainted: GX 5.3.18-5-default #1 SLE15-SP2 (unreleased) > Krnl PSW : 0704e00180000000 0000001ecd281b9e (__kernel_map_pages+0x166/0x188) > R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3 > Krnl GPRS: 0000000000000000 0000000000000800 0000400b00000000 0000000000000100 > 0000000000000001 0000000000000000 0000000000000002 0000000000000100 > 0000001ece139230 0000001ecdd98d40 0000400b00000100 0000000000000000 > 000003ffa17e4000 001fffe0114f7d08 0000001ecd4d93ea 001fffe0114f7b20 > Krnl Code: 0000001ecd281b8e: ec17ffff00d8 ahik %r1,%r7,-1 > 0000001ecd281b94: ec111dbc0355 risbg %r1,%r1,29,188,3 >> 0000001ecd281b9e: 94fb5006 ni 6(%r5),251 > 0000001ecd281ba2: 41505008 la %r5,8(%r5) > 0000001ecd281ba6: ec51fffc6064 cgrj %r5,%r1,6,1ecd281b9e > 0000001ecd281bac: 1a07 ar %r0,%r7 > 0000001ecd281bae: ec03ff584076 crj %r0,%r3,4,1ecd281a5e > Call Trace: > [<0000001ecd281b9e>] __kernel_map_pages+0x166/0x188 > [<0000001ecd4d9516>] online_pages_range+0xf6/0x128 > [<0000001ecd2a8186>] walk_system_ram_range+0x7e/0xd8 > [<0000001ecda28aae>] online_pages+0x2fe/0x3f0 > [<0000001ecd7d02a6>] memory_subsys_online+0x8e/0xc0 > [<0000001ecd7add42>] device_online+0x5a/0xc8 > [<0000001ecd7d0430>] state_store+0x88/0x118 > [<0000001ecd5b9f62>] kernfs_fop_write+0xc2/0x200 > [<0000001ecd5064b6>] vfs_write+0x176/0x1e0 > [<0000001ecd50676a>] ksys_write+0xa2/0x100 > [<0000001ecda315d4>] system_call+0xd8/0x2c8 > > Fix this by checking debug_pagealloc_enabled_static() before calling > kernel_map_pages(). Backports for kernel before 5.5 should use > debug_pagealloc_enabled() instead. Also add comments. > > Fixes: cd02cf1aceea ("mm/hotplug: fix an imbalance with DEBUG_PAGEALLOC") > Reported-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> > Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> > Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > Cc: Qian Cai <cai@xxxxxx> > Link: http://lkml.kernel.org/r/20200224094651.18257-1-vbabka@xxxxxxx > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > > --- > include/linux/mm.h | 4 ++++ > mm/memory_hotplug.c | 8 +++++++- > 2 files changed, 11 insertions(+), 1 deletion(-) > > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2695,6 +2695,10 @@ static inline bool debug_pagealloc_enabl > #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) > { > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -598,7 +598,13 @@ EXPORT_SYMBOL_GPL(__online_page_free); > > static void generic_online_page(struct page *page, unsigned int order) > { > - kernel_map_pages(page, 1 << order, 1); > + /* > + * Freeing the page with debug_pagealloc enabled will try to unmap it, > + * so we should map it first. This is better than introducing a special > + * case in page freeing fast path. > + */ > + if (debug_pagealloc_enabled_static()) Won't build on 5.4, see in changelog "Backports for kernel before 5.5 should use debug_pagealloc_enabled() instead." > + kernel_map_pages(page, 1 << order, 1); > __free_pages_core(page, order); > totalram_pages_add(1UL << order); > #ifdef CONFIG_HIGHMEM > > > Patches currently in stable-queue which might be from vbabka@xxxxxxx are > > queue-5.4/mm-numa-fix-bad-pmd-by-atomically-check-for-pmd_trans_huge-when-marking-page-tables-prot_numa.patch > queue-5.4/mm-hotplug-fix-page-online-with-debug_pagealloc-compiled-but-not-enabled.patch > queue-5.4/mm-fix-possible-pmd-dirty-bit-lost-in-set_pmd_migration_entry.patch >
