RE: Qemu Guest kernel 4.20-rc1 PCIe hotplug issue

[Shameerali Kolothum Thodi]

> -----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.

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