linux-kernel - Re: [PATCH] iommu/vt-d: Fix modify

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Date:   Mon, 22 Aug 2016 21:32:56 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        iommu@...ts.linux-foundation.org,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Joerg Roedel <joro@...tes.org>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] iommu/vt-d: Fix modify_irte NULL pointer

2016-08-22 20:38 GMT+08:00 Thomas Gleixner <tglx@...utronix.de>:
> On Mon, 22 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
>>           -> parse_ioapics_under_ir   => return 0
>>                   -> ir_parse_ioapic_hpet_scope
>>                     -> ir_parse_one_ioapic_scope
>>           -> intel_setup_irq_remapping
>
>> IR table is setup even if noapic boot parameter is added.
>> index ac59692..f1cb7c6 100644
>> --- a/drivers/iommu/intel_irq_remapping.c
>> +++ b/drivers/iommu/intel_irq_remapping.c
>> @@ -854,6 +854,9 @@ static int ir_parse_one_ioapic_scope(struct acpi_dmar_device_scope *scope,
>>       count = (scope->length - sizeof(struct acpi_dmar_device_scope))
>>               / sizeof(struct acpi_dmar_pci_path);
>>
>> +     if (skip_ioapic_setup)
>> +             return -ENODEV;
>
> Why are you adding this in the iommu code? We should not call any of the apic
> functions when apic is disabled.

Good point, how about something like this(untested, I will test it tomorrow):

diff --git a/arch/x86/kernel/apic/probe_32.c b/arch/x86/kernel/apic/probe_32.c
index 7c43e71..152d627 100644
--- a/arch/x86/kernel/apic/probe_32.c
+++ b/arch/x86/kernel/apic/probe_32.c
@@ -154,6 +154,9 @@ void __init default_setup_apic_routing(void)
 {
        int version = apic_version[boot_cpu_physical_apicid];

+       if (skip_ioapic_setup)
+               return;
+
        if (num_possible_cpus() > 8) {
                switch (boot_cpu_data.x86_vendor) {
                case X86_VENDOR_INTEL:
diff --git a/arch/x86/kernel/apic/probe_64.c b/arch/x86/kernel/apic/probe_64.c
index c303054..ffc3ae2 100644
--- a/arch/x86/kernel/apic/probe_64.c
+++ b/arch/x86/kernel/apic/probe_64.c
@@ -29,6 +29,9 @@ void __init default_setup_apic_routing(void)
 {
        struct apic **drv;

+       if (skip_ioapic_setup)
+               return;
+
        enable_IR_x2apic();

Regards,
Wanpeng Li