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

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Date:   Thu, 4 Jan 2018 18:07:12 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Thomas Zeitlhofer <thomas.zeitlhofer+lkml@...it.at>,
        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 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?

---
diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index 8f0aace08b87..8156e47da7ba 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -5,6 +5,7 @@
 
 #include <asm/cpu_entry_area.h>
 #include <asm/perf_event.h>
+#include <asm/tlbflush.h>
 #include <asm/insn.h>
 
 #include "../perf_event.h"
@@ -283,20 +284,35 @@ static DEFINE_PER_CPU(void *, insn_buffer);
 
 static void ds_update_cea(void *cea, void *addr, size_t size, pgprot_t prot)
 {
+	unsigned long start = (unsigned long)cea;
 	phys_addr_t pa;
 	size_t msz = 0;
 
 	pa = virt_to_phys(addr);
+
+	preempt_disable();
 	for (; msz < size; msz += PAGE_SIZE, pa += PAGE_SIZE, cea += PAGE_SIZE)
 		cea_set_pte(cea, pa, prot);
+
+	/*
+	 * This is a cross-CPU update of the cpu_entry_area, we must shoot down
+	 * all TLB entries for it.
+	 */
+	flush_tlb_kernel_range(start, start + size);
+	preempt_enable();
 }
 
 static void ds_clear_cea(void *cea, size_t size)
 {
+	unsigned long start = (unsigned long)cea;
 	size_t msz = 0;
 
+	preempt_disable();
 	for (; msz < size; msz += PAGE_SIZE, cea += PAGE_SIZE)
 		cea_set_pte(cea, 0, PAGE_NONE);
+
+	flush_tlb_kernel_range(start, start + size);
+	preempt_enable();
 }
 
 static void *dsalloc_pages(size_t size, gfp_t flags, int cpu)