linux-kernel - Re: [PATCH v2] x86/apic: Fix modify

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Date:   Tue, 23 Aug 2016 19:47:07 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>, Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH v2] x86/apic: Fix modify_irte NULL pointer

2016-08-23 19:31 GMT+08:00 Thomas Gleixner <tglx@...utronix.de>:
> On Tue, 23 Aug 2016, Wanpeng Li wrote:
>
>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>
>> native_smp_prepare_cpus
>>   -> default_setup_apic_routing
>>     -> enable_IR_x2apic
>>       -> irq_remapping_prepare
>>         -> intel_prepare_irq_remapping
>>           -> intel_setup_irq_remapping
>>
>> IR table is setup even if noapic boot parameter is added.
>>
>> As a result:
>>
>>     BUG: unable to handle kernel NULL pointer dereference at           (null)
>>     IP: [<ffffffff8d5a5e58>] modify_irte+0x58/0x140
>>     PGD 209638067 PUD 2105f4067 PMD 0
>>     Oops: 0000 [#1] SMP
>>     RIP: 0010:[<ffffffff8d5a5e58>]  [<ffffffff8d5a5e58>] modify_irte+0x58/0x140
>>     Call Trace:
>>      intel_ir_set_affinity+0xa3/0xb0
>>      msi_domain_set_affinity+0x21/0x70
>>      ? __irq_set_affinity+0x34/0x70
>>      irq_do_set_affinity+0x1d/0x70
>>      irq_set_affinity_locked+0xc2/0x100
>>      __irq_set_affinity+0x47/0x70
>>      write_irq_affinity.isra.7+0xcc/0xf0
>>      irq_affinity_proc_write+0x19/0x20
>>      proc_reg_write+0x3d/0x70
>>      ? rcu_sync_lockdep_assert+0x2f/0x60
>>      __vfs_write+0x28/0x120
>>      ? percpu_down_read+0x5c/0xa0
>>      ? __sb_start_write+0xca/0xe0
>>      ? __sb_start_write+0xca/0xe0
>>      vfs_write+0xb5/0x1b0
>>      SyS_write+0x49/0xa0
>>      do_syscall_64+0x81/0x220
>>      entry_SYSCALL64_slow_path+0x25/0x25
>>     RIP  [<ffffffff8d5a5e58>] modify_irte+0x58/0x140
>>      RSP <ffff8e9ad01b7c78>
>>     CR2: 0000000000000000
>>
>> irqbalance is running at the end of booting and changes the irq affinity,
>> then irte is flushed. We should not have MSI and such if apic is disabled.
>> This patch fix it by return -ENODEV if apic is disabled in order to avoid
>> to setup ir table for ioapic.
>
> I don't see any ENODEV here in the patch. This changelog sucks. The problem is

It is the leftover in v1.

> neither irqbalance nor MSI. The problem is simply that we try to setup irq
> remapping even if "noapic" is on the kernel command line and therefor ioapic
> support is disabled.
>
>> @@ -154,6 +154,9 @@ void __init default_setup_apic_routing(void)
>>  {
>>       int version = apic_version[boot_cpu_physical_apicid];
>>
>> +     if (skip_ioapic_setup)
>> +             return;
>
> So you skip the whole APIC setup as well. APIC != IOAPIC. This check belongs
> into enable_IR_x2apic().

I just aware noapic boot parameter disables ioapic instead of lapic +
ioapic. I will send out another version to fix it.

Regards,
Wanpeng Li