Re: [Xen-devel] Xen-unstable: pci-passthrough regression bisected to: x86/smp: use APIC ALLBUT destination shorthand when possible

["Roger Pau Monné" <roger.pau@citrix.com>]

Ping?

On Mon, Feb 03, 2020 at 02:21:08PM +0100, Roger Pau Monné wrote:
> On Mon, Feb 03, 2020 at 01:44:06PM +0100, Sander Eikelenboom wrote:
> > On 03/02/2020 13:41, Roger Pau Monné wrote:
> > > On Mon, Feb 03, 2020 at 01:30:55PM +0100, Sander Eikelenboom wrote:
> > >> On 03/02/2020 13:23, Roger Pau Monné wrote:
> > >>> On Mon, Feb 03, 2020 at 09:33:51AM +0100, Sander Eikelenboom wrote:
> > >>>> Hi Roger,
> > >>>>
> > >>>> Last week I encountered an issue with the PCI-passthrough of a USB controller. 
> > >>>> In the guest I get:
> > >>>>     [ 1143.313756] xhci_hcd 0000:00:05.0: xHCI host not responding to stop endpoint command.
> > >>>>     [ 1143.334825] xhci_hcd 0000:00:05.0: xHCI host controller not responding, assume dead
> > >>>>     [ 1143.347364] xhci_hcd 0000:00:05.0: HC died; cleaning up
> > >>>>     [ 1143.356407] usb 1-2: USB disconnect, device number 2
> > >>>>
> > >>>> Bisection turned up as the culprit: 
> > >>>>    commit 5500d265a2a8fa63d60c08beb549de8ec82ff7a5
> > >>>>    x86/smp: use APIC ALLBUT destination shorthand when possible
> > >>>
> > >>> Sorry to hear that, let see if we can figure out what's wrong.
> > >>
> > >> No problem, that is why I test stuff :)
> > >>
> > >>>> I verified by reverting that commit and now it works fine again.
> > >>>
> > >>> Does the same controller work fine when used in dom0?
> > >>
> > >> Will test that, but as all other pci devices in dom0 work fine,
> > >> I assume this controller would also work fine in dom0 (as it has also
> > >> worked fine for ages with PCI-passthrough to that guest and still works
> > >> fine when reverting the referenced commit).
> > > 
> > > Is this the only device that fails to work when doing pci-passthrough,
> > > or other devices also don't work with the mentioned change applied?
> > > 
> > > Have you tested on other boxes?
> > > 
> > >> I don't know if your change can somehow have a side effect
> > >> on latency around the processing of pci-passthrough ?
> > > 
> > > Hm, the mentioned commit should speed up broadcast IPIs, but I don't
> > > see how it could slow down other interrupts. Also I would think the
> > > domain is not receiving interrupts from the device, rather than
> > > interrupts being slow.
> > > 
> > > Can you also paste the output of lspci -v for that xHCI device from
> > > dom0?
> > > 
> > > Thanks, Roger.
> > 
> > Will do this evening including the testing in dom0 etc.
> > Will also see if there is any pattern when observing /proc/interrupts in
> > the guest.
> 
> Thanks! I also have some trivial patch that I would like you to try,
> just to discard send_IPI_mask clearing the scratch_cpumask under
> another function feet.
> 
> Roger.
> ---
> diff --git a/xen/arch/x86/smp.c b/xen/arch/x86/smp.c
> index 65eb7cbda8..aeeb506155 100644
> --- a/xen/arch/x86/smp.c
> +++ b/xen/arch/x86/smp.c
> @@ -66,7 +66,8 @@ static void send_IPI_shortcut(unsigned int shortcut, int vector,
>  void send_IPI_mask(const cpumask_t *mask, int vector)
>  {
>      bool cpus_locked = false;
> -    cpumask_t *scratch = this_cpu(scratch_cpumask);
> +    static DEFINE_PER_CPU(cpumask_t, send_ipi_cpumask);
> +    cpumask_t *scratch = &this_cpu(send_ipi_cpumask);
>  
>      /*
>       * This can only be safely used when no CPU hotplug or unplug operations
> 
> 
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