Re: [patch 7/7] PCI/AER: Fix the broken interrupt injection

[Kuppuswamy Sathyanarayanan]

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@xxxxxxxxxxxxxxx>
Tested-by: Kuppuswamy Sathyanarayanan 
<sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> Fixes: 390e2db82480 ("PCI/AER: Abstract AER interrupt handling")
> Reported-by: sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> ---
>   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