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; } _
