The patch titled
Subject: kfence, x86: fix preemptible warning on KPTI-enabled systems
has been added to the -mm tree. Its filename is
kfence-x86-fix-preemptible-warning-on-kpti-enabled-systems.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/kfence-x86-fix-preemptible-warning-on-kpti-enabled-systems.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/kfence-x86-fix-preemptible-warning-on-kpti-enabled-systems.patch
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------------------------------------------------------
From: Marco Elver <elver@xxxxxxxxxx>
Subject: kfence, x86: fix preemptible warning on KPTI-enabled systems
On systems with KPTI enabled, we can currently observe the following
warning:
BUG: using smp_processor_id() in preemptible
caller is invalidate_user_asid+0x13/0x50
CPU: 6 PID: 1075 Comm: dmesg Not tainted 5.12.0-rc4-gda4a2b1a5479-kfence_1+ #1
Hardware name: Hewlett-Packard HP Pro 3500 Series/2ABF, BIOS 8.11 10/24/2012
Call Trace:
dump_stack+0x7f/0xad
check_preemption_disabled+0xc8/0xd0
invalidate_user_asid+0x13/0x50
flush_tlb_one_kernel+0x5/0x20
kfence_protect+0x56/0x80
...
While it normally makes sense to require preemption to be off, so that the
expected CPU's TLB is flushed and not another, in our case it really is
best-effort (see comments in kfence_protect_page()).
Avoid the warning by disabling preemption around flush_tlb_one_kernel().
Link: https://lore.kernel.org/lkml/YGIDBAboELGgMgXy@xxxxxxxxxxxxxxxx/
Link: https://lkml.kernel.org/r/20210330065737.652669-1-elver@xxxxxxxxxx
Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
Reported-by: Tomi Sarvela <tomi.p.sarvela@xxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/kfence.h | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
--- a/arch/x86/include/asm/kfence.h~kfence-x86-fix-preemptible-warning-on-kpti-enabled-systems
+++ a/arch/x86/include/asm/kfence.h
@@ -56,8 +56,13 @@ static inline bool kfence_protect_page(u
else
set_pte(pte, __pte(pte_val(*pte) | _PAGE_PRESENT));
- /* Flush this CPU's TLB. */
+ /*
+ * Flush this CPU's TLB, assuming whoever did the allocation/free is
+ * likely to continue running on this CPU.
+ */
+ preempt_disable();
flush_tlb_one_kernel(addr);
+ preempt_enable();
return true;
}
_
Patches currently in -mm which might be from elver@xxxxxxxxxx are
kfence-x86-fix-preemptible-warning-on-kpti-enabled-systems.patch
kfence-zero-guard-page-after-out-of-bounds-access.patch
