Re: [Xen-devel] [PATCH] xen_pt: fix failure of attaching & detaching a PCI device to VM repeatedly

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 3 Dec 2015, Jianzhong,Chang wrote:
> From: jianzhong,Chang <jianzhongx.chang@xxxxxxxxx>
> 
> Add pci = [ '$VF_BDF', '$VF_BDF', '$VF_BDF'] in

This is a bit confusing: it is not actually correct to assign the same
device, even an SR_IOV VF, multiple times, so these must be all
different. More like:

pci = [ '$VF_BDF1', '$VF_BDF2', '$VF_BDF3']


> hvm guest configuration file. After the guest boot up,
> detach the VFs in sequence by "xl pci-detach $DOMID $VF_BDF",
> reattach the VFs by "xl pci-attach $VF_BDF" in sequence.

So do you mean:

xl pci-detach $DOMID $VF_BDF1
xl pci-detach $DOMID $VF_BDF2
xl pci-detach $DOMID $VF_BDF3
xl pci-attach $DOMID $VF_BDF1
xl pci-attach $DOMID $VF_BDF2
xl pci-attach $DOMID $VF_BDF3

?


> An error message will be reported like this:
> "libxl: error: libxl_qmp.c:287:qmp_handle_error_response: received
> an error message from QMP server: Duplicate ID 'pci-pt-07_10.1' for device"
> 
> When xen_pt_region_add/del() is called, MemoryRegion
> may not belong to the XenPCIPassthroughState.
> xen_pt_region_update() checks it but memory_region_ref/unref() does not.
> This case causes obj->ref issue and affects the release of related objects.
> So, the detection operation is moved from
> xen_pt_region_update to xen_pt_region_add/del.
> 
> Signed-off-by: Jianzhong,Chang <jianzhongx.chang@xxxxxxxxx>
> ---
>  hw/xen/xen_pt.c |   23 ++++++++++++++++++++---
>  1 files changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/xen/xen_pt.c b/hw/xen/xen_pt.c
> index aa96288..95b4970 100644
> --- a/hw/xen/xen_pt.c
> +++ b/hw/xen/xen_pt.c
> @@ -523,6 +523,14 @@ static int xen_pt_bar_from_region(XenPCIPassthroughState 
> *s, MemoryRegion *mr)
>      }
>      return -1;
>  }
> +static bool xen_pt_region_in_state(XenPCIPassthroughState *s, MemoryRegion 
> *mr)
> +{
> +    int bar = xen_pt_bar_from_region(s, mr);
> +    if (-1 == bar && (!s->msix || &s->msix->mmio != mr)) {
> +        return false;
> +    }
> +    return true;
> +}
>  
>  /*
>   * This function checks if an io_region overlaps an io_region from another
> @@ -587,9 +595,6 @@ static void xen_pt_region_update(XenPCIPassthroughState 
> *s,
>      };
>  
>      bar = xen_pt_bar_from_region(s, mr);
> -    if (bar == -1 && (!s->msix || &s->msix->mmio != mr)) {
> -        return;
> -    }
>  
>      if (s->msix && &s->msix->mmio == mr) {
>          if (adding) {
> @@ -642,6 +647,9 @@ static void xen_pt_region_add(MemoryListener *l, 
> MemoryRegionSection *sec)
>      XenPCIPassthroughState *s = container_of(l, XenPCIPassthroughState,
>                                               memory_listener);
>  
> +    if (!xen_pt_region_in_state(s, sec->mr)) {
> +        return;
> +    }
>      memory_region_ref(sec->mr);
>      xen_pt_region_update(s, sec, true);
>  }
> @@ -651,6 +659,9 @@ static void xen_pt_region_del(MemoryListener *l, 
> MemoryRegionSection *sec)
>      XenPCIPassthroughState *s = container_of(l, XenPCIPassthroughState,
>                                               memory_listener);
>  
> +    if (!xen_pt_region_in_state(s, sec->mr)) {
> +        return;
> +    }
>      xen_pt_region_update(s, sec, false);
>      memory_region_unref(sec->mr);
>  }
> @@ -660,6 +671,9 @@ static void xen_pt_io_region_add(MemoryListener *l, 
> MemoryRegionSection *sec)
>      XenPCIPassthroughState *s = container_of(l, XenPCIPassthroughState,
>                                               io_listener);
>  
> +    if (!xen_pt_region_in_state(s, sec->mr)) {
> +        return;
> +    }
>      memory_region_ref(sec->mr);
>      xen_pt_region_update(s, sec, true);
>  }
> @@ -669,6 +683,9 @@ static void xen_pt_io_region_del(MemoryListener *l, 
> MemoryRegionSection *sec)
>      XenPCIPassthroughState *s = container_of(l, XenPCIPassthroughState,
>                                               io_listener);
>  
> +    if (!xen_pt_region_in_state(s, sec->mr)) {
> +        return;
> +    }
>      xen_pt_region_update(s, sec, false);
>      memory_region_unref(sec->mr);
>  }

Wouldn't it make more sense to move the
memory_region_ref/memory_region_unref calls inside xen_pt_region_update?

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