Messages in this thread | | | Date | Wed, 11 Mar 2020 12:04:47 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH -next] x86/mm/pat: mark an intentional data race |
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On Wed, Mar 11, 2020 at 05:17:56PM +0100, Borislav Petkov wrote: > + Paul. > > On Mon, Feb 10, 2020 at 09:10:16AM -0500, Qian Cai wrote: > > cpa_4k_install could be accessed concurrently as noticed by KCSAN, > > > > read to 0xffffffffaa59a000 of 8 bytes by interrupt on cpu 7: > > cpa_inc_4k_install arch/x86/mm/pat/set_memory.c:131 [inline] > > __change_page_attr+0x10cf/0x1840 arch/x86/mm/pat/set_memory.c:1514 > > __change_page_attr_set_clr+0xce/0x490 arch/x86/mm/pat/set_memory.c:1636 > > __set_pages_np+0xc4/0xf0 arch/x86/mm/pat/set_memory.c:2148 > > __kernel_map_pages+0xb0/0xc8 arch/x86/mm/pat/set_memory.c:2178 > > kernel_map_pages include/linux/mm.h:2719 [inline] <snip> > > > > write to 0xffffffffaa59a000 of 8 bytes by task 1 on cpu 6: > > cpa_inc_4k_install arch/x86/mm/pat/set_memory.c:131 [inline] > > __change_page_attr+0x10ea/0x1840 arch/x86/mm/pat/set_memory.c:1514 > > __change_page_attr_set_clr+0xce/0x490 arch/x86/mm/pat/set_memory.c:1636 > > __set_pages_p+0xc4/0xf0 arch/x86/mm/pat/set_memory.c:2129 > > __kernel_map_pages+0x2e/0xc8 arch/x86/mm/pat/set_memory.c:2176 > > kernel_map_pages include/linux/mm.h:2719 [inline] <snip> > > > > Both accesses are due to the same "cpa_4k_install++" in > > cpa_inc_4k_install. A data race here could be potentially undesirable: > > depending on compiler optimizations or how x86 executes a non-LOCK'd > > increment, it may lose increments, corrupt the counter, etc. Since this > > counter only seems to be used for printing some stats, this data race > > itself is unlikely to cause harm to the system though. Thus, mark this > > intentional data race using the data_race() marco. > > > > Suggested-by: Macro Elver <elver@google.com> > > Signed-off-by: Qian Cai <cai@lca.pw> > > --- > > arch/x86/mm/pat/set_memory.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c > > index c4aedd00c1ba..ea0b6df950ee 100644 > > --- a/arch/x86/mm/pat/set_memory.c > > +++ b/arch/x86/mm/pat/set_memory.c > > @@ -128,7 +128,7 @@ static inline void cpa_inc_2m_checked(void) > > > > static inline void cpa_inc_4k_install(void) > > { > > - cpa_4k_install++; > > + data_race(cpa_4k_install++); > > } > > > > static inline void cpa_inc_lp_sameprot(int level) > > -- > > Acked-by: Borislav Petkov <bp@suse.de>
Applied, thank you both!
Thanx, Paul
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