linux-kernel - Re: [PATCHv2 4/6] iommu/intel: Handle DMAR faults on workqueue

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Message-ID: <1518543533.2849.25.camel@arista.com>
Date:   Tue, 13 Feb 2018 17:38:53 +0000
From:   Dmitry Safonov <dima@...sta.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     linux-kernel@...r.kernel.org, 0x7f454c46@...il.com,
        Alex Williamson <alex.williamson@...hat.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        iommu@...ts.linux-foundation.org
Subject: Re: [PATCHv2 4/6] iommu/intel: Handle DMAR faults on workqueue

On Tue, 2018-02-13 at 17:35 +0100, Joerg Roedel wrote:
> On Mon, Feb 12, 2018 at 04:48:23PM +0000, Dmitry Safonov wrote:
> > dmar_fault() reports/handles/cleans DMAR faults in a cycle one-by-
> > one.
> > The nuisance is that it's set as a irq handler and runs with
> > disabled
> > interrupts - which works OK if you have only a couple of DMAR
> > faults,
> > but becomes a problem if your intel iommu has a plenty of mappings.
> 
> I don't think that a work-queue is the right solution here, it adds a
> long delay until the log is processed. During that delay, and with
> high
> fault rates the error log will overflow during that delay.
> 
> Here is what I think you should do instead to fix the soft-lockups:
> 
> First, unmask the fault reporting irq so that you will get subsequent
> irqs. Then:
> 
> 	* For Primary Fault Reporting just cycle once through all
> 	  supported fault recording registers.
> 
> 	* For Advanced Fault Reporting, read start and end pointer of
> 	  the log and process all entries.
> 
> After that return from the fault handler and let the next irq handle
> additional faults that might have been recorded while the previous
> handler was running.

Ok, will re-do this way, thanks.

> And of course, ratelimiting the fault printouts is always a good
> idea.

-- 
            Dima