Re: [Xen-devel] [BUG] Xen vm kernel crash in get_free_entries.

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 26 Nov 2013, Konrad Rzeszutek Wilk wrote:
> On Wed, Nov 13, 2013 at 09:40:58AM +0000, Ian Campbell wrote:
> > On Tue, 2013-11-12 at 10:56 -0500, Konrad Rzeszutek Wilk wrote:
> > > On Thu, Nov 07, 2013 at 01:47:03PM +0000, Ian Campbell wrote:
> > > > On Thu, 2013-11-07 at 09:20 +0400, Astarta wrote:
> > > > > Hello,
> > > > > 
> > > > > Let me bring some new life to this discussion.
> > > > > 
> > > > > I've investigated a bit and found another way to make  kernels 
> > > > > starting 
> > > > > from 3.8.x to boot on the VMs with platform device_id 0002.
> > > > > Reverting of 
> > > > > xen-grant-table-correctly-initialize-grant-table-version-1 
> > > > > patch is not necessary.
> > > > > 
> > > > > We can simply modify struct pci_device_id platform_pci_tbl[] (in 
> > > > > drivers/xen/platform-pci.c) to respect 0002 and 0000 device ids.
> > > > > That makes the kernel (3.8.x and 3.11.6) to boot correctly, disks and 
> > > > > network are also recognized.
> > > > 
> > > > I think this is just working around the problem, by avoiding the
> > > > situation where the error occurs. You could just as well switch to
> > > > platform device id < 2.
> > > 
> > > I am bit late to this discussion - but shouldn't there be something
> > > in the kernel to deal with this?
> > 
> > Well, ideally the kernel wouldn't crash ;-)
> 
> This patch should solve that (untested, but at least compile tested):
> Please test it.
> 
> >From f7d3581aa19a35ea3ff10b965b2b08843e923635 Mon Sep 17 00:00:00 2001
> From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Date: Tue, 26 Nov 2013 15:05:40 -0500
> Subject: [PATCH] xen/pvhvm: If xen_platform_pci=0 is set don't blow up.
> 
> *TODO*
> 
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> ---
>  drivers/block/xen-blkfront.c               |  2 +-
>  drivers/input/misc/xen-kbdfront.c          |  4 ++++
>  drivers/net/xen-netfront.c                 |  2 +-
>  drivers/xen/xenbus/xenbus_probe_frontend.c |  2 +-
>  include/xen/platform_pci.h                 | 13 +++++++++++++
>  5 files changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 432db1b..bcbaf0b 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -2074,7 +2074,7 @@ static int __init xlblk_init(void)
>       if (!xen_domain())
>               return -ENODEV;
>  
> -     if (xen_hvm_domain() && !xen_platform_pci_unplug)
> +     if (xen_err_out())
>               return -ENODEV;
>  
>       if (register_blkdev(XENVBD_MAJOR, DEV_NAME)) {
> diff --git a/drivers/input/misc/xen-kbdfront.c 
> b/drivers/input/misc/xen-kbdfront.c
> index e21c181..9d250cf 100644
> --- a/drivers/input/misc/xen-kbdfront.c
> +++ b/drivers/input/misc/xen-kbdfront.c
> @@ -29,6 +29,7 @@
>  #include <xen/interface/io/fbif.h>
>  #include <xen/interface/io/kbdif.h>
>  #include <xen/xenbus.h>
> +#include <xen/platform_pci.h>
>  
>  struct xenkbd_info {
>       struct input_dev *kbd;
> @@ -380,6 +381,9 @@ static int __init xenkbd_init(void)
>       if (xen_initial_domain())
>               return -ENODEV;
>  
> +     if (xen_err_out())
> +             return -ENODEV;

Why do we error out here? There is nothing to unplug in this case.


>       return xenbus_register_frontend(&xenkbd_driver);
>  }
>  
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index e59acb1..be2744b 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -2115,7 +2115,7 @@ static int __init netif_init(void)
>       if (!xen_domain())
>               return -ENODEV;
>  
> -     if (xen_hvm_domain() && !xen_platform_pci_unplug)
> +     if (xen_err_out())
>               return -ENODEV;
>  
>       pr_info("Initialising Xen virtual ethernet driver\n");
> diff --git a/drivers/xen/xenbus/xenbus_probe_frontend.c 
> b/drivers/xen/xenbus/xenbus_probe_frontend.c
> index 129bf84..b1c0f2a 100644
> --- a/drivers/xen/xenbus/xenbus_probe_frontend.c
> +++ b/drivers/xen/xenbus/xenbus_probe_frontend.c
> @@ -496,7 +496,7 @@ subsys_initcall(xenbus_probe_frontend_init);
>  #ifndef MODULE
>  static int __init boot_wait_for_devices(void)
>  {
> -     if (xen_hvm_domain() && !xen_platform_pci_unplug)
> +     if (xen_err_out())
>               return -ENODEV;
>  
>       ready_to_wait_for_devices = 1;
> diff --git a/include/xen/platform_pci.h b/include/xen/platform_pci.h
> index 438c256..a5bbd0b 100644
> --- a/include/xen/platform_pci.h
> +++ b/include/xen/platform_pci.h
> @@ -47,5 +47,18 @@ static inline int xen_must_unplug_disks(void) {
>  }
>  
>  extern int xen_platform_pci_unplug;
> +static  bool xen_err_out(void)
> +{

static inline


> +     if (!xen_domain())
> +             return true;
> +
> +     if (xen_hvm_domain()) {
> +             if (xen_platform_pci_unplug & (XEN_UNPLUG_UNNECESSARY | 
> XEN_UNPLUG_NEVER))

This check wasn't present before and I don't think should be present
now: xen_platform_pci_unplug cannot be set to XEN_UNPLUG_NEVER, see the
beginning of xen_unplug_emulated_devices. Also XEN_UNPLUG_UNNECESSARY is
meant to say that the user knows what she is doing and no unplug is
necessary to safely use PV drivers, see the commit message of
1dc7ce99b091a11cce0f34456c1ffcb928f17edd.


> +                     return true;
> +             if (xen_platform_pci_unplug == 0)
> +                     return true;
> +     }
> +     return false;
> +}
>  #endif /* _XEN_PLATFORM_PCI_H */


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