Re: [PATCH 2.6.20.3] Flush writes to MSI-X table

Kok, Auke
2007-03-23T21:50:57Z

Greg KH wrote:
> On Thu, Mar 22, 2007 at 02:08:19PM -0700, Mitch Williams wrote:
>> Because both MSI-X interrupt messages and MSI-X table writes are posted,
>> it's possible for them to cross while in-flight. This results in
>> interrupts being received long after the kernel thinks they're disabled,
>> and in interrupts being sent to stale vectors after rebalancing.
>>
>> This patch performs a read flush after writes to the MSI-X table for
>> enable/disable and rebalancing operations. Because this is an expensive
>> operation, we do not perform the read flush after mask/unmask
>> operations. Hardware which supports MSI-X typically also supports some
>> sort of interrupt moderation, so a read-flush is not necessary for
>> mask/unmask operations.
>>
>> This patch has been validated with (unreleased) network hardware which
>> uses MSI-X.
>
> Is this needed for any hardware that is public today?

yes. Every msi-x capable piece of hardware in the field will crash if it does
any form of interrupt balancing. (okay that is not that much stuff out there...
I know, but the patch is not that big at all - all it does is subtly add a few
read flushes to make sure that critical changes in the msix vector tables are
pushed out at the proper time).

> Also, it seems a bit too big of a patch for -stable right now,
> especially as the mainline patch will not make it into 2.6.22 at the
> earliest.

I think Mitch was way too sensitive when he worded his e-mail. We should really
be trying to get this fix into 2.6.21 at least.

Mitch, can you re-post this and include Eric Biederman, linux-pci, our intel
platform guys and perhaps Linus and Andrew?

A lot of vendors (not just us) will be pushing msi-x capable hardware out, and
this fix is absolutely needed. Getting it in soon is really preferred. Not to
mention that Mitch has spent well over 8 weeks I think making sure that this is
indeed the issue and the proper fix...

Auke