Date:	Fri, 22 May 2015 21:53:37 -0400
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	david.vrabel@...rix.com, linux@...elenboom.it
CC:	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [Xen-devel] Regression due to "device property: Make it possible
 to use secondary firmware nodes" Re: Xen-unstable + linux 4.1-mergewindow:
 problems with PV guest pci passthrough: pcifront pci-0: pciback not responding!!!

On 05/22/2015 04:11 AM, Sander Eikelenboom wrote:
> Hello Sander,
>
> Friday, May 15, 2015, 12:47:27 AM, you wrote:
>
>> Sorry for the resend, i messed up the to's en from's.
>
>> Hi Konrad / David,
>
>> One big snip on this thread, got some more debug info, hopefully this will
>> lead to something:
>
>> On a working kernel (with the two seemingly non related patches reverted) i get:
>
>> [    0.717796] pcifront pci-0: Allocated pdev @ 0xffff880019e11780 pdev->sh_info @ 0xffff880018f58000
>> [    0.717848] pcifront pci-0: ?!?!? before alloc gntref: 0
>> [    0.717871] pcifront pci-0: ?!?!? after alloc gntref: 8
>> [    0.717892] pcifront pci-0: ?!?!? before alloc evtchn: -1
>> [    0.717915] pcifront pci-0: ?!?!? after alloc evtchn: 17
>> [    0.717984] pcifront pci-0: ?!?!? bound evtchn:17 to irqhandler:-1 err:31
>> [    0.721640] pcifront pci-0: publishing successful!
>> [    0.723684] usbcore: registered new interface driver udlfb
>> [    0.724664] xen:xen_evtchn: Event-channel device installed
>> [    0.726597] pcifront pci-0: Installing PCI frontend
>> [    0.726853] Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled
>> [    0.727059] pcifront pci-0: Creating PCI Frontend Bus 0000:00
>> [    0.727363] pcifront pci-0: PCI host bridge to bus 0000:00
>> [    0.727391] pci_bus 0000:00: root bus resource [io  0x0000-0xffff]
>> [    0.727417] pci_bus 0000:00: root bus resource [mem 0x00000000-0xffffffffffff]
>> [    0.727452] pci_bus 0000:00: root bus resource [bus 00-ff]
>> [    0.727475] pci_bus 0000:00: scanning bus
>> [    0.727503] pcifront pci-0: read dev=0000:00:00.0 - offset 0 size 4
>> [    0.728253] Linux agpgart interface v0.103
>> [    0.728387] Hangcheck: starting hangcheck timer 0.9.1 (tick is 180 seconds, margin is 60 seconds).
>> [    0.728474] [drm] Initialized drm 1.1.0 20060810
>> [    0.728551] [drm] radeon kernel modesetting enabled.
>> [    0.730319] pcifront pci-0: ?!?!? pciback responded !!! irq:31 irq_flags:ffff880019e100a8 ns: 1431641785551700000  ns_timeout: 1431641787541235000 evtchn:17 gnt_ref:8
>> [    0.730319] pcifront pci-0: ?!?!? op cmd:0 err:0 info:0 offset:0 size:4
>> [    0.730319] pcifront pci-0: ?!?!? active_op cmd:0 err:0 info:0 offset:0 size:4
>> [    0.730319] pcifront pci-0: read got back value 11113f6
>> [    0.738845] pcifront pci-0: read dev=0000:00:00.0 - offset e size 1
>> [    0.744976] brd: module loaded
>> [    0.745204] pcifront pci-0: ?!?!? pciback responded !!! irq:31 irq_flags:ffff880019e100a8 ns: 1431641785562852000  ns_timeout: 1431641787552580000 evtchn:17 gnt_ref:8
>> [    0.745204] pcifront pci-0: ?!?!? op cmd:0 err:0 info:0 offset:14 size:1
>> [    0.745204] pcifront pci-0: ?!?!? active_op cmd:0 err:0 info:0 offset:14 size:1
>> [    0.745204] pcifront pci-0: read got back value 0
>> [    0.749204] pcifront pci-0: read dev=0000:00:00.0 - offset 6 size 2
>> [    0.750155] loop: module loaded
>> [    0.752527] pcifront pci-0: ?!?!? pciback responded !!! irq:31 irq_flags:ffff880019e100a8 ns: 1431641785570841000  ns_timeout: 1431641787562917000 evtchn:17 gnt_ref:8
>> [    0.752527] pcifront pci-0: ?!?!? op cmd:0 err:0 info:0 offset:6 size:2
>> [    0.752527] pcifront pci-0: ?!?!? active_op cmd:0 err:0 info:0 offset:6 size:2
>> [    0.752527] pcifront pci-0: read got back value 210
>> [    0.757187] pcifront pci-0: read dev=0000:00:00.0 - offset 34 size 1
>
>
>> Were as in the non-working situation i get:
>
>> [    0.751244] pcifront pci-0: Allocated pdev @ 0xffff880019ec2e00 pdev->sh_info @ 0xffff88001aa51000
>> [    0.751295] pcifront pci-0: ?!?!? before alloc gntref: 0
>> [    0.751315] pcifront pci-0: ?!?!? after alloc gntref: 8
>> [    0.751334] pcifront pci-0: ?!?!? before alloc evtchn: -1
>> [    0.751355] pcifront pci-0: ?!?!? after alloc evtchn: 17
>> [    0.751422] pcifront pci-0: ?!?!? bound evtchn:17 to irqhandler:-1 err:31
>> [    0.755215] pcifront pci-0: publishing successful!
>> [    0.757341] usbcore: registered new interface driver udlfb
>> [    0.758365] xen:xen_evtchn: Event-channel device installed
>> [    0.760419] Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled
>> [    0.760819] pcifront pci-0: Installing PCI frontend
>> [    0.761518] pcifront pci-0: Creating PCI Frontend Bus 0000:00
>> [    0.761684] pcifront pci-0: PCI host bridge to bus 0000:00
>> [    0.761710] pci_bus 0000:00: root bus resource [io  0x0000-0xffff]
>> [    0.761733] pci_bus 0000:00: root bus resource [mem 0x00000000-0xffffffffffff]
>> [    0.761763] pci_bus 0000:00: root bus resource [bus 00-ff]
>> [    0.761783] pci_bus 0000:00: scanning bus
>> [    0.761805] pcifront pci-0: read dev=0000:00:00.0 - offset 0 size 4
>> [    0.767207] Linux agpgart interface v0.103
>> [    0.767362] Hangcheck: starting hangcheck timer 0.9.1 (tick is 180 seconds, margin is 60 seconds).
>> [    0.767439] [drm] Initialized drm 1.1.0 20060810
>> [    0.767515] [drm] radeon kernel modesetting enabled.
>> [    0.766948] pcifront pci-0: pciback not responding!!! irq:31 irq_flags:ffff880019ec0028 ns: 1431641983026498000  ns_timeout: 1431641983026497000 evtchn:0 gnt_ref:0
>> [    0.766948] pcifront pci-0: ?!?!? op cmd:0 err:0 info:0 offset:0 size:4
>> [    0.766948] pcifront pci-0: ?!?!? active_op cmd:0 err:0 info:0 offset:0 size:4
>> [    0.766948] pcifront pci-0: other err read got back err: ffffffff value: 0
>> [    2.762062] pcifront pci-0: read dev=0000:00:01.0 - offset 0 size 4
>> [    2.765203] pcifront pci-0: pciback not responding!!! irq:31 irq_flags:ffff880019ec0028 ns: 1431641985026742000  ns_timeout: 1431641985026741000 evtchn:0 gnt_ref:0
>> [    2.765203] pcifront pci-0: ?!?!? op cmd:0 err:0 info:0 offset:0 size:4
>> [    2.765203] pcifront pci-0: ?!?!? active_op cmd:0 err:0 info:0 offset:0 size:4
>> [    2.765203] pcifront pci-0: other err read got back err: ffffffff value: 0
>> [    4.762172] pcifront pci-0: read dev=0000:00:02.0 - offset 0 size 4
>> [    4.764231] brd: module loaded
>> [    4.765508] loop: module loaded
>> [    4.766748] pcifront pci-0: pciback not responding!!! irq:31 irq_flags:ffff880019ec0028 ns: 1431641987026850000  ns_timeout: 1431641987026849000 evtchn:0 gnt_ref:0
>> [    4.766748] pcifront pci-0: ?!?!? op cmd:0 err:0 info:0 offset:0 size:4
>> [    4.766748] pcifront pci-0: ?!?!? active_op cmd:0 err:0 info:0 offset:0 size:4
>> [    4.766748] pcifront pci-0: other err read got back err: ffffffff value: 0
>> [    6.762248] pcifront pci-0: read dev=0000:00:03.0 - offset 0 size 4
>> [    6.765545] pcifront pci-0: pciback not responding!!! irq:31 irq_flags:ffff880019ec0028 ns: 1431641989026930000  ns_timeout: 1431641989026929000 evtchn:0 gnt_ref:0
>> [    6.765545] pcifront pci-0: ?!?!? op cmd:0 err:0 info:0 offset:0 size:4
>> [    6.765545] pcifront pci-0: ?!?!? active_op cmd:0 err:0 info:0 offset:0 size:4
>> [    6.765545] pcifront pci-0: other err read got back err: ffffffff value: 0
>> [    8.762329] pcifront pci-0: read dev=0000:00:04.0 - offset 0 size 4
>> [    8.765626] pcifront pci-0: pciback not responding!!! irq:31 irq_flags:ffff880019ec0028 ns: 1431641991027006000  ns_timeout: 1431641991027005000 evtchn:0 gnt_ref:0
>> [    8.765626] pcifront pci-0: ?!?!? op cmd:0 err:0 info:0 offset:0 size:4
>> [    8.765626] pcifront pci-0: ?!?!? active_op cmd:0 err:0 info:0 offset:0 size:4
>> [    8.765626] pcifront pci-0: other err read got back err: ffffffff value: 0
>> [   10.762410] pcifront pci-0: read dev=0000:00:05.0 - offset 0 size 4
>> [   10.765701] pcifront pci-0: pciback not responding!!! irq:31 irq_flags:ffff880019ec0028 ns: 1431641993027087000  ns_timeout: 1431641993027086000 evtchn:0 gnt_ref:0
>> [   10.765701] pcifront pci-0: ?!?!? op cmd:0 err:0 info:0 offset:0 size:4
>> [   10.765701] pcifront pci-0: ?!?!? active_op cmd:0 err:0 info:0 offset:0 size:4
>> [   10.765701] pcifront pci-0: other err read got back err: ffffffff value: 0
>> [   12.762472] pcifront pci-0: read dev=0000:00:06.0 - offset 0 size 4
>
>
>> So somehow in the non-working situation, pdev->evtchn and pdev->gnt_ref are 0 in
>> xen-pcifront.c:do_pci_op(), so no wonder it's not getting a response back ...
>
>> Question is .. why ?
>
>> --
>> Sander
>
>
> Ping ?
>
> David / Boris,
>
> Any idea, since Konrad seems to be off for 2 weeks and we are at rc4 now.
>

(+Rafael again)

So the immediate cause of those errors is that pdev->evtchn is 0. 
Backend is not notified and things not go well then.

And it is indeed caused by 97badf873ab60e841243b66133ff9eff2a46ef29:

We allocate pcifront_sd in pcifront_scan_root() and then pass it to 
pci_scan_bus_parented() as sysdata. Eventually this sysdata is used in 
pcibios_root_bridge_prepare() as pci_sysdata. It is dereferenced as 
pci_sysdata->companion (which I believe is aliased to pcifront_sd->pdev) 
and then set_primary_fwnode() writes it, thus corrupting 
pcifront_sd->pdev (and I think this is what sets evtchn to zero).

I don't have a fix for that. I will see what we can do on Tuesday since 
I am out on Monday.

Question to Rafael about commit 97badf873ab60e84124: is it really safe 
to assume that bridge->bus->sysdata is a pointer to  pci_sysdata in 
pcibios_root_bridge_prepare()? It is declared as 'void *'.

-boris


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