linux-kernel - Re: "BUG: using smp_processor_id() in preemptible" with KPTI on 4.14.11

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Message-ID: <20180104183800.ewx42etmmzk5b544@toau>
Date:   Thu, 4 Jan 2018 19:38:00 +0100
From:   Thomas Zeitlhofer <thomas.zeitlhofer+lkml@...it.at>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: "BUG: using smp_processor_id() in preemptible" with KPTI on
 4.14.11

On Thu, Jan 04, 2018 at 06:07:12PM +0100, Peter Zijlstra wrote:
> On Thu, Jan 04, 2018 at 04:37:24PM +0100, Thomas Gleixner wrote:
> > > Yes:
> > > 
> > >    BUG: using smp_processor_id() in preemptible [00000000] code: ovsdb-server/4498
> > >    caller is native_flush_tlb_single+0x57/0xc0
> > >    CPU: 2 PID: 4498 Comm: ovsdb-server Not tainted 4.15.0-rc6-kvm-00423-gea1908c252eb #3
> > >    Hardware name: MSI MS-7798/B75MA-P45 (MS-7798), BIOS V1.9 09/30/2013
> > >    Call Trace:
> > >     dump_stack+0x5c/0x86
> > >     check_preemption_disabled+0xdd/0xe0
> > >     native_flush_tlb_single+0x57/0xc0
> > >     ? __set_pte_vaddr+0x2d/0x40
> > >     __set_pte_vaddr+0x2d/0x40
> > >     set_pte_vaddr+0x2f/0x40
> > >     cea_set_pte+0x30/0x40
> > >     ds_update_cea.constprop.4+0x4d/0x70
> > >     reserve_ds_buffers+0x159/0x410
> > >     ? wp_page_copy+0x370/0x6c0
> > >     x86_reserve_hardware+0x150/0x160
> > >     x86_pmu_event_init+0x3e/0x1f0
> > >     perf_try_init_event+0x69/0x80
> > >     perf_event_alloc+0x652/0x740
> > >     SyS_perf_event_open+0x3f6/0xd60
> > >     do_syscall_64+0x5c/0x190
> > >     entry_SYSCALL64_slow_path+0x25/0x25
> > >    RIP: 0033:0x72bff0a3c0b9
> > >    RSP: 002b:00007ffed11c2f18 EFLAGS: 00000206 ORIG_RAX: 000000000000012a
> > >    RAX: ffffffffffffffda RBX: 00007ffed11c30f0 RCX: 000072bff0a3c0b9
> > >    RDX: 00000000ffffffff RSI: 0000000000000000 RDI: 00007ffed11c2f20
> > >    RBP: 0000000000000000 R08: 0000000000000000 R09: 0000007000000000
> > >    R10: 00000000ffffffff R11: 0000000000000206 R12: 0000000000000008
> > >    R13: 0000000000000000 R14: 00007ffed11c30d0 R15: 000060986ecfb600
> 
> Fun, so set_pte_vaddr() and the whole cpu_entry_area are supposed to be
> per CPU. But the DS crud does cross CPU updates of those tables.
> 
> So we need some additional fun and games..
> 
> How's the below?
[...]

Looks good - I have successfully tested it on top of 4.14.11 and
4.15-rc6. In both cases, the error message is gone when this patch is
applied.

Thanks,

Thomas