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Date:   Fri, 6 Mar 2020 11:29:30 -0800
From:   Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Marc Zyngier <maz@...nel.org>, x86@...nel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        Keith Busch <kbusch@...nel.org>
Subject: Re: [patch 7/7] PCI/AER: Fix the broken interrupt injection


On 3/6/20 10:32 AM, Kuppuswamy Sathyanarayanan wrote:
>
> On 3/6/20 5:03 AM, Thomas Gleixner wrote:
>> The AER error injection mechanism just blindly abuses 
>> generic_handle_irq()
>> which is really not meant for consumption by random drivers. The 
>> include of
>> linux/irq.h should have been a red flag in the first place. Driver code,
>> unless implementing interrupt chips or low level hypervisor 
>> functionality
>> has absolutely no business with that.
>>
>> Invoking generic_handle_irq() from non interrupt handling context can 
>> have
>> nasty side effects at least on x86 due to the hardware trainwreck which
>> makes interrupt affinity changes a fragile beast. Sathyanarayanan 
>> triggered
>> a NULL pointer dereference in the low level APIC code that way. While 
>> the
>> particular pointer could be checked this would only paper over the issue
>> because there are other ways to trigger warnings or silently corrupt 
>> state.
>>
>> Invoke the new irq_inject_interrupt() mechanism, which has the necessary
>> sanity checks in place and injects the interrupt via the irq_retrigger()
>> mechanism, which is at least halfways safe vs. the fragile x86 affinity
>> change mechanics.
>>
>> It's safe on x86 as it does not corrupt state, but it still can cause a
>> premature completion of an interrupt affinity change causing the 
>> interrupt
>> line to become stale. Very unlikely, but possible.
>>
>> For regular operations this is a non issue as AER error injection is 
>> meant
>> for debugging and testing and not for usage on production systems. 
>> People
>> using this should better know what they are doing.
> It looks good to me.
>
> Reviewed-by: Kuppuswamy Sathyanarayanan 
> <sathyanarayanan.kuppuswamy@...ux.intel.com>
> Tested-by: Kuppuswamy Sathyanarayanan 
> <sathyanarayanan.kuppuswamy@...ux.intel.com>
>>
>> Fixes: 390e2db82480 ("PCI/AER: Abstract AER interrupt handling")
This patch is merged in v4.20 kernel. So this fix could be a candidate 
for stable fix.
>> Reported-by: sathyanarayanan.kuppuswamy@...ux.intel.com
>> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
>> ---
>>   drivers/pci/pcie/Kconfig      |    1 +
>>   drivers/pci/pcie/aer_inject.c |    6 ++----
>>   2 files changed, 3 insertions(+), 4 deletions(-)
>>
>> --- a/drivers/pci/pcie/Kconfig
>> +++ b/drivers/pci/pcie/Kconfig
>> @@ -34,6 +34,7 @@ config PCIEAER
>>   config PCIEAER_INJECT
>>       tristate "PCI Express error injection support"
>>       depends on PCIEAER
>> +    select GENERIC_IRQ_INJECTION
>>       help
>>         This enables PCI Express Root Port Advanced Error Reporting
>>         (AER) software error injector.
>> --- a/drivers/pci/pcie/aer_inject.c
>> +++ b/drivers/pci/pcie/aer_inject.c
>> @@ -16,7 +16,7 @@
>>     #include <linux/module.h>
>>   #include <linux/init.h>
>> -#include <linux/irq.h>
>> +#include <linux/interrupt.h>
>>   #include <linux/miscdevice.h>
>>   #include <linux/pci.h>
>>   #include <linux/slab.h>
>> @@ -468,9 +468,7 @@ static int aer_inject(struct aer_error_i
>>           }
>>           pci_info(edev->port, "Injecting errors %08x/%08x into 
>> device %s\n",
>>                einj->cor_status, einj->uncor_status, pci_name(dev));
>> -        local_irq_disable();
>> -        generic_handle_irq(edev->irq);
>> -        local_irq_enable();
>> +        ret = irq_inject_interrupt(edev->irq);
>>       } else {
>>           pci_err(rpdev, "AER device not found\n");
>>           ret = -ENODEV;
>>
-- 
Sathyanarayanan Kuppuswamy
Linux kernel developer

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