Date:	Mon, 29 Apr 2013 20:34:17 +0000
From:	"Duran, Leo" <leo.duran@....com>
To:	Don Dutile <ddutile@...hat.com>,
	"Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>
CC:	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: RFC: IOMMU/AMD: Error Handling

I'm wondering if resetting the IOMMU at init-time (once) would clear any BIOS induced noise.
Leo

> -----Original Message-----
> From: iommu-bounces@...ts.linux-foundation.org [mailto:iommu-
> bounces@...ts.linux-foundation.org] On Behalf Of Don Dutile
> Sent: Monday, April 29, 2013 3:10 PM
> To: Suthikulpanit, Suravee
> Cc: iommu@...ts.linux-foundation.org; linux-kernel@...r.kernel.org
> Subject: Re: RFC: IOMMU/AMD: Error Handling
> 
> On 04/29/2013 03:45 PM, Suravee Suthikulanit wrote:
> > Joerg,
> >
> > We are in the process of implementing AMD IOMMU error handling, and I
> would like some comments from you and the community.
> >
> > Currently, the AMD IOMMU driver only reports events from the event log
> in the dmesg, and does not try to handle them in case of errors. AMD
> IOMMU errors can be categorized as device-specific errors and IOMMU
> errors.
> >
> > 1. For IOMMU errors such as:
> > - DEV_TAB_HADWARE_ERROR
> > - PAGE_TAB_ERROR
> > - COMMAND_HARDWARE_ERROR
> > If the error is detected during IOMMU initialization, we could disable
> IOMMU and proceed. If the error occurs after IOMMU is initialized, we won't
> be able to recover from this, and might need to result in panic.
> >
> > 2. For device-specific errors such as:
> > - ILLEGAL_DEV_TABLE_ENTRY
> > - IO_PAGE_FAULT
> > - INVALDE_DEVICE_REQUEST
> > We think the AMD IOMMU driver should try to isolate the device. This
> involves blocking device transactions at IOMMU DTE and tries to disable the
> device (e.g. calling the remove(struct pci_dev *pdev) interface generally
> provides by device drivers). This could prevents the device from continuing
> to fail and to risk of system instability.
> >
> disabling the device is not an option.
> We've seen mis-configured ACPI tables generate storms of invalide dte
> messages after iommu setup but before they are cleared up when the OS
> driver is started & resets the device. The original storm is from bios-use of
> IOMMU with a device.
> I'd recommend creating a filter that prevents further logging from a device
> for 5 mins at a time if a storm of DTE-related errors are seen.
> by definition, the DMA is blocked from corrupting/changing memory, so
> isolation has been established; keeping the failure log from consuming the
> system is the needed fix.
> 
> > 3. In case of posted memory write transaction, device driver might not be
> aware that the transaction has failed and blocked at IOMMU. If there is no
> HW IOMMU, I believe this is handled by PCI error handling code. If the
> IOMMU hardware reporth such case, could this potentially leverage the
> Linux IOMMU fault handling interface, iommu_set_fault_handler() and
> report_iommu_fault(), to communicate to device driver or PCI driver?
> >
> Wondering if you could use AER-like callback mechanism so a driver can be
> invoked when IOMMU error occurs, so the device driver can quiesce or reset
> the device if it deems it transient.
> 
> 
> > Any feedback or comments are appreciated.
> >
> > Thank you,
> > Suravee
> >
> >
> >
> >
> > _______________________________________________
> > iommu mailing list
> > iommu@...ts.linux-foundation.org
> > https://lists.linuxfoundation.org/mailman/listinfo/iommu
> 
> _______________________________________________
> iommu mailing list
> iommu@...ts.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu


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