RE: Qemu Guest kernel 4.20-rc1 PCIe hotplug issue

[Shameerali Kolothum Thodi]

> -----Original Message-----
> From: Linuxarm [mailto:linuxarm-bounces@xxxxxxxxxx] On Behalf Of
> Shameerali Kolothum Thodi
> Sent: 13 November 2018 12:36
> To: mika.westerberg@xxxxxxxxxxxxxxx
> Cc: linux-pci@xxxxxxxxxxxxxxx; Lukas Wunner <lukas@xxxxxxxxx>; linux-
> kernel@xxxxxxxxxxxxxxx; Linuxarm <linuxarm@xxxxxxxxxx>
> Subject: RE: Qemu Guest kernel 4.20-rc1 PCIe hotplug issue
> 
> 
> 
> > -----Original Message-----
> > From: mika.westerberg@xxxxxxxxxxxxxxx
> > [mailto:mika.westerberg@xxxxxxxxxxxxxxx]
> > Sent: 13 November 2018 12:25
> > To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@xxxxxxxxxx>
> > Cc: linux-pci@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Wangzhou (B)
> > <wangzhou1@xxxxxxxxxxxxx>; Linuxarm <linuxarm@xxxxxxxxxx>; Lukas
> > Wunner <lukas@xxxxxxxxx>
> > Subject: Re: Qemu Guest kernel 4.20-rc1 PCIe hotplug issue
> >
> > +Lukas
> >
> > On Tue, Nov 13, 2018 at 11:45:42AM +0000, Shameerali Kolothum Thodi
> wrote:
> > > Hi Mika,
> >
> > Hi,
> >
> > > Since the commit commit 720d6a671a6e("PCI: pciehp: Do not handle events
> > > if interrupts are masked"), the hotplug support on Qemu Guest(4.120-rc1)
> > > with a vfio passthrough device seems to be broken. This is on an ARM64
> > platform.
> > >
> > > I am booting a Guest with below command line options with the intention of
> > > hot add a ixgbevf dev later,
> > >
> > > ./qemu-system-aarch64 -machine virt,kernel_irqchip=on,gic-version=3 -cpu
> > host \
> > >  -kernel Image_4.20-rc1 \
> > >  -initrd rootfs-iperf.cpio \
> > >  -device ioh3420,id=rp1 \
> > >  -net none \
> > >  -m 4096 \
> > >  -nographic -D -d -enable-kvm \
> > >  -append "console=ttyAMA0 root=/dev/vda -m 4096 rw
> > pciehp.pciehp_debug=1
> > >   pcie_ports=native searlycon=pl011,0x9000000"
> > >
> > > But receives this on boot,
> > >
> > > [    1.327852] pciehp 0000:00:01.0:pcie004: Timeout
> > > on hotplug command 0x03f1 (issued 1016 msec ago)
> > > [    1.335842] pciehp 0000:00:01.0:pcie004: Timeout on hotplug command
> > > 0x03f1 (issued 1024 msec ago)
> > > [    3.847843] pciehp 0000:00:01.0:pcie004: Failed to check link status
> > > [    3.855843] pciehp 0000:00:01.0:pcie004: Timeout on hotplug command
> > > 0x02f1 (issued 2520 msec ago)
> > > [    4.879846] pciehp 0000:00:01.0:pcie004: Timeout on hotplug command
> > > 0x06f1 (issued 1024 msec ago)
> > > [    5.911840] pciehp 0000:00:01.0:pcie004: Timeout on hotplug command
> > > 0x06f1 (issued 2056 msec ago)
> > > [    6.927844] pciehp 0000:00:01.0:pcie004: Timeout on hotplug command
> > > 0x07f1 (issued 1016 msec ago)
> > > [    7.951843] pciehp 0000:00:01.0:pcie004: Timeout on hotplug command
> > > 0x0771 (issued 1024 msec ago)
> > >
> > > Trying to hot add using "device_addvfio-
> > pci,host=0000:01:10.1,id=net0,bus=rp1"
> > > doesn't work either. And if I boot the guest with an assigned device
> > > (-device vfio-pci,host=0000:01:10.1,id=net0,bus=rp1), I can see the dev
> listed
> > in
> > > the Guest but then hot remove doesn't work.
> > >
> > > This all works on 4.19 and bisect points to the above mentioned commit,
> > where an
> > > additional check is added in pciehp_isr(),
> > >
> > > -	 * Interrupts only occur in D3hot or shallower (PCIe r4.0, sec 6.7.3.4).
> > > +	 * Interrupts only occur in D3hot or shallower and only if enabled
> > > +	 * in the Slot Control register (PCIe r4.0, sec 6.7.3.4).
> > >  	 */
> > > -	if (pdev->current_state == PCI_D3cold)
> > > +	if (pdev->current_state == PCI_D3cold ||
> > > +	    (!(ctrl->slot_ctrl & PCI_EXP_SLTCTL_HPIE) && !pciehp_poll_mode))
> > >  		return IRQ_NONE;
> > >
> > > I think this doesn't work for the first time, where the cmd with
> > PCI_EXP_SLTCTL_HPIE bit set
> > > is written,
> > > pciehp_probe()
> > >   pcie_init_notification()
> > >     pcie_enable_notification()
> > >        pcie_do_write_cmd()
> > >
> > > to begin with, ctrl->slot_ctrl = 0 in pciehp_isr() as this is only set once the
> > write
> > > is returned.
> > >
> > > Or else I am missing something here. Please take a look and let me know.
> >
> > Thanks for the detailed report and analysis. I think you are right and
> > the ctrl->slot_ctrl is only set after the actual value has been
> > programmed to the hardware, so if there was interrupt "pending" it will
> > trigger immediately (just to find ctrl->slot_ctrl == 0).
> >
> > I wonder if the following change helps here?
> >
> > diff --git a/drivers/pci/hotplug/pciehp_hpc.c
> > b/drivers/pci/hotplug/pciehp_hpc.c
> > index 7dd443aea5a5..cd9eae650aa5 100644
> > --- a/drivers/pci/hotplug/pciehp_hpc.c
> > +++ b/drivers/pci/hotplug/pciehp_hpc.c
> > @@ -156,9 +156,9 @@ static void pcie_do_write_cmd(struct controller *ctrl,
> > u16 cmd,
> >  	slot_ctrl |= (cmd & mask);
> >  	ctrl->cmd_busy = 1;
> >  	smp_mb();
> > +	ctrl->slot_ctrl = slot_ctrl;
> 
> Actually I tried this one, but it doesn't help in this case as the initial
> pcie_capability_read_word() returns the slot_ctrl without
> PCI_EXP_SLTCTL_HPIE
> bit set.  It looks to me  pcie_enable_notification() function enables this,
> 
> 	if (!pciehp_poll_mode)
> 		cmd |= PCI_EXP_SLTCTL_HPIE | PCI_EXP_SLTCTL_CCIE;
> 
> I don't know this is as per the spec or not as the initial cap read doesn't seems
> to
> have the PCI_EXP_SLTCTL_HPIE bit set.

Hang on..I think this should work as you are setting the ctrl->slot_ctrl after updating
it with the cmd | mask. I will try this and report back.

Thanks,
Shameer
 
> Thanks,
> Shameer
> 
> >  	pcie_capability_write_word(pdev, PCI_EXP_SLTCTL, slot_ctrl);
> >  	ctrl->cmd_started = jiffies;
> > -	ctrl->slot_ctrl = slot_ctrl;
> >
> >  	/*
> >  	 * Controllers with the Intel CF118 and similar errata advertise
> 
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