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Thu, 01 Apr 2021 02:11:31 -0700 (PDT) MIME-Version: 1.0 References: <20210330065737.652669-1-elver@google.com> In-Reply-To: <20210330065737.652669-1-elver@google.com> From: Alexander Potapenko Date: Thu, 1 Apr 2021 11:11:19 +0200 Message-ID: Subject: Re: [PATCH mm] kfence, x86: fix preemptible warning on KPTI-enabled systems To: Marco Elver Cc: Andrew Morton , Dmitriy Vyukov , Andrey Konovalov , Jann Horn , LKML , Linux Memory Management List , kasan-dev , "the arch/x86 maintainers" , Tomi Sarvela Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: C51AD2000262 X-Stat-Signature: z78nrcxy5yttjqtbmq1mu7dttg7swsz5 Received-SPF: none (google.com>: No applicable sender policy available) receiver=imf11; identity=mailfrom; envelope-from=""; helo=mail-qk1-f169.google.com; client-ip=209.85.222.169 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617268290-727355 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Mar 30, 2021 at 8:57 AM Marco Elver wrote: > > 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@elver.google.com/ > Reported-by: Tomi Sarvela > Signed-off-by: Marco Elver Acked-by: Alexander Potapenko