Message-ID: <1768370.Rs1vKzEP4D@vostro.rjw.lan>
Date:	Tue, 26 May 2015 01:22:12 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Sander Eikelenboom <linux@...elenboom.it>
Cc:	david.vrabel@...rix.com, linux@...elenboom.it,
	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
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 Friday, May 22, 2015 09:53:37 PM Boris Ostrovsky wrote:
> 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).

Thanks for the analysis!

OK, so the pcibios_root_bridge_prepare() in arch/x86/pci/acpi.c assumes
that bridge->bus->sysdata points to a struct pci_sysdata which has a
'companion' of type struct acpi_device.

This is supposed to come from pci_acpi_scan_root() and not something else.

> 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 *'.

That's because other architectures pass different things through it IIRC.

It should be a struct pci_sysdata pointer on x86 and ia64 at least.  It is a bug
otherwise and things only worked by accident before.  In particular, the ACPI
companion of bridge->dev was set to something random located at the end of
the struct pcifront_sd or behind it (on 64 bit).  If referenced, that would
crash the kernel.

Padding struct pcifront_sd to match the layout of struct pci_sysdata should
make it work.  Of course, a real fix would be to use a different
pcibios_root_bridge_prepare() for Xen.

Sander, can you please check if the patch below (untested) makes any difference?

---
 drivers/pci/xen-pcifront.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Index: linux-pm/drivers/pci/xen-pcifront.c
===================================================================
--- linux-pm.orig/drivers/pci/xen-pcifront.c
+++ linux-pm/drivers/pci/xen-pcifront.c
@@ -53,6 +53,8 @@ struct pcifront_device {
 
 struct pcifront_sd {
 	int domain;
+	int node;
+	void *padding[2];
 	struct pcifront_device *pdev;
 };
 
@@ -465,7 +467,7 @@ static int pcifront_scan_root(struct pci
 		 domain, bus);
 
 	bus_entry = kmalloc(sizeof(*bus_entry), GFP_KERNEL);
-	sd = kmalloc(sizeof(*sd), GFP_KERNEL);
+	sd = kzalloc(sizeof(*sd), GFP_KERNEL);
 	if (!bus_entry || !sd) {
 		err = -ENOMEM;
 		goto err_out;

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