lkml.org 
[lkml]   [2013]   [May]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] xen: reuse the same pirq allocated when driver load first time
On Fri, 10 May 2013, Konrad Rzeszutek Wilk wrote:
> On Wed, May 08, 2013 at 04:18:24PM +0800, Zhenzhong Duan wrote:
> > When driver load and unload in a loop, pirq will exhaust finally.
> > Try to use the same pirq which was already mapped and binded at first time
>
> So what happens if I unload and reload two drivers in random order?
>
> > when driver loaded.
> >
> > Read pirq from msix entry and test if data is XEN_PIRQ_MSI_DATA
> > xen_irq_from_pirq(pirq) < 0 checking is wrong as irq will be freed
> > when driver unload, it's always true in second load.
>
> If my understanding is right the issue at hand is that the caching
> information about the pirq disappears once the driver has been
> unloaded b/c the event's irq-info is removed (as the driver is
> unloaded and free_irq is called).
>
> Stefano,
> Is there a specific write to the MSI structure that would cause the
> hypervisor to drop the PIRQ? Or a nice hypercall to "free" an
> PIRQ in usage?

We already have a "free PIRQ" hypercall, it's called
PHYSDEVOP_unmap_pirq and should be called by QEMU.
Linux should disable the MSI bit in the PCI config options of the
device:

pci_disable_msi -> pci_msi_shutdown -> msi_set_enable(0)

That should cause QEMU to issue a xc_physdev_unmap_pirq that actually
unmaps the pirq. If it doesn't, it's a bug :)


> I presume that on the first load the msg.data value is
> ALWAYS != XEN_PIRQ_MSI_DATA right? Is that somethign we can ALWAYS
> depend? Or is there a possibility that it could be that when the
> PCI device is unplugged from one guest and plugged in another?
>
> Could we use PHYSDEVOP_irq_status_query to figure out if the PIRQ
> has been already allocated? Ah, does not look like it.
>
> I am a bit worried about depending on just msg.data to tells us
> whether the device had been initialized before.

Data comes from QEMU, I think it is zeroed at init time.


\
 
 \ /
  Last update: 2013-05-13 13:41    [W:0.114 / U:0.652 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site