Re: [PATCH] xen/pvhvm: If xen_platform_pci=0 is set don't blow up.

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

Hi Konrad,

On Tue, Dec 03, 2013 at 04:14:06PM -0500, Konrad Rzeszutek Wilk wrote:
> The user has the option of disabling the platform driver:
> 00:02.0 Unassigned class [ff80]: XenSource, Inc. Xen Platform Device (rev 01)
> 
> which is used to unplug the emulated drivers (IDE, Realtek 8169, etc)
> and allow the PV drivers to take over. If the user wishes
> to disable that they can set:
> 
>   xen_platform_pci=0
>   (in the guest config file)
> 
> or
>   xen_emul_unplug=never
>   (on the Linux command line)
> 
> except it does not work properly. The PV drivers still try to
> load and since the Xen platform driver is not run - and it
> has not initialized the grant tables, most of the PV drivers
> stumble upon:
> 
> input: Xen Virtual Keyboard as /devices/virtual/input/input5
> input: Xen Virtual Pointer as /devices/virtual/input/input6M
> ------------[ cut here ]------------
> kernel BUG at /home/konrad/ssd/konrad/linux/drivers/xen/grant-table.c:1206!
> invalid opcode: 0000 [#1] SMP
> Modules linked in: xen_kbdfront(+) xenfs xen_privcmd
> CPU: 6 PID: 1389 Comm: modprobe Not tainted 3.13.0-rc1upstream-00021-ga6c892b-dirty #1
> Hardware name: Xen HVM domU, BIOS 4.4-unstable 11/26/2013
> RIP: 0010:[<ffffffff813ddc40>]  [<ffffffff813ddc40>] get_free_entries+0x2e0/0x300
> Call Trace:
>  [<ffffffff8150d9a3>] ? evdev_connect+0x1e3/0x240
>  [<ffffffff813ddd0e>] gnttab_grant_foreign_access+0x2e/0x70
>  [<ffffffffa0010081>] xenkbd_connect_backend+0x41/0x290 [xen_kbdfront]
>  [<ffffffffa0010a12>] xenkbd_probe+0x2f2/0x324 [xen_kbdfront]
>  [<ffffffff813e5757>] xenbus_dev_probe+0x77/0x130
>  [<ffffffff813e7217>] xenbus_frontend_dev_probe+0x47/0x50
>  [<ffffffff8145e9a9>] driver_probe_device+0x89/0x230
>  [<ffffffff8145ebeb>] __driver_attach+0x9b/0xa0
>  [<ffffffff8145eb50>] ? driver_probe_device+0x230/0x230
>  [<ffffffff8145eb50>] ? driver_probe_device+0x230/0x230
>  [<ffffffff8145cf1c>] bus_for_each_dev+0x8c/0xb0
>  [<ffffffff8145e7d9>] driver_attach+0x19/0x20
>  [<ffffffff8145e260>] bus_add_driver+0x1a0/0x220
>  [<ffffffff8145f1ff>] driver_register+0x5f/0xf0
>  [<ffffffff813e55c5>] xenbus_register_driver_common+0x15/0x20
>  [<ffffffff813e76b3>] xenbus_register_frontend+0x23/0x40
>  [<ffffffffa0015000>] ? 0xffffffffa0014fff
>  [<ffffffffa001502b>] xenkbd_init+0x2b/0x1000 [xen_kbdfront]
>  [<ffffffff81002049>] do_one_initcall+0x49/0x170
> 
> .. snip..
> 
> which is hardly nice. This patch fixes this by having each
> PV driver check for:
>  - if running in PV, then it is fine to execute (as that is their
>    native environment).
>  - if running in HVM, check if user wanted 'xen_emul_unplug=never',
>    in which case bail out and don't load PV drivers.
>  - if running in HVM, and if PCI device 5853:0001 (xen_platform_pci)
>    does not exist, then bail out and not load PV drivers.
> 
> P.S.
> Ian Campbell suggested getting rid of 'xen_platform_pci_unplug'
> but unfortunatly the xen-blkfront driver is using it, so we
> cannot do it.
> 
> Reported-by: Sander Eikelenboom <linux@eikelenboom.it
> Reported-by: Anthony PERARD <anthony.perard@citrix.com>
> Reported-by: Fabio Fantoni <fabio.fantoni@m2r.biz>

For input:

Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

...

> +#if defined(CONFIG_XEN_PVHVM)
> +extern bool xen_has_pv_devices(void);
> +#else
> +static inline bool xen_has_pv_devices(void)
> +{
> +#if defined(CONFIG_XEN)
> +	return true;
> +#else
> +	return false;
> +#endif

	return IS_ENABLED(CONFIG_XEN);

?

Thanks.

-- 
Dmitry