Subject: Re: [Xen-devel] [PATCH v3 1/2] xen/pvhvm: If xen_platform_pci=0 is set don't blow up (v3).

From: Konrad Rzeszutek Wilk <[email-masked]>
Date: Thu, 2 Jan 2014 14:16:09 -0500

On Thu, Jan 02, 2014 at 03:09:44PM +0000, David Vrabel wrote:
> On 31/12/13 14:32, Konrad Rzeszutek Wilk wrote:
> >> That is because 'disks' is incorrect. It should have been 'ide-disks'
> >>
> >> [    0.000000] unrecognised option 'disks' in parameter 'xen_emul_unplug'
> >>
> >> With the 'ide-disks' it should work. I will update the description to
> >> mention 'ide-disks' instead of 'disks'. Thank you for finding this!
> >>
> > 
> > I've v4 with said update and will push it to Linus shortly.
> > 
> > Thanks!
> > 
> > P.S.
> > Here is v4:
> > 
> >>From 275a81e7496d3532e5b4752703c50a7c8355a6c7 Mon Sep 17 00:00:00 2001
> > From: Konrad Rzeszutek Wilk <[email-masked]>
> > Date: Tue, 26 Nov 2013 15:05:40 -0500
> > Subject: [PATCH] xen/pvhvm: If xen_platform_pci=0 is set don't blow up (v4).
> > 
> > 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 any 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.
> >  - (v2) if running in HVM, and if the user wanted 'xen_emul_unplug=ide-disks',
> >    then bail out for all PV devices _except_ the block one.
> >    Ditto for the network one ('nics').
> >  - (v2) if running in HVM, and if the user wanted 'xen_emul_unplug=unnecessary'
> >    then load block PV driver, and also setup the legacy IDE paths.
> >    In (v3) make it actually load PV drivers.
> [...]
> > --- a/arch/x86/xen/platform-pci-unplug.c
> > +++ b/arch/x86/xen/platform-pci-unplug.c
> > @@ -69,6 +69,80 @@ static int check_platform_magic(void)
> >  	return 0;
> >  }
> >  
> > +bool xen_has_pv_devices()
> > +{
> > +	if (!xen_domain())
> > +		return false;
> > +
> > +	/* PV domains always have them. */
> > +	if (xen_pv_domain())
> > +		return true;
> > +
> > +	/* And user has xen_platform_pci=0 set in guest config as
> > +	 * driver did not modify the value. */
> > +	if (xen_platform_pci_unplug == 0)
> > +		return false;
> > +
> > +	if (xen_platform_pci_unplug & XEN_UNPLUG_NEVER)
> > +		return false;
> > +
> > +	if (xen_platform_pci_unplug & XEN_UNPLUG_ALL)
> > +		return true;
> > +
> > +	/* This is an odd one - we are going to run legacy
> > +	 * and PV drivers at the same time. */
> > +	if (xen_platform_pci_unplug & XEN_UNPLUG_UNNECESSARY)
> > +		return true;
> > +
> > +	/* And the caller has to follow with xen_pv_{disk,nic}_devices
> > +	 * to be certain which driver can load. */
> > +	return false;
> 
> This may result in:
> 
> xen_has_pv_devices() == false
> xen_has_pv_disk_devices() == true

Yes.
> 
> which looks odd to me.  Surely xen_has_pv_*_devices() is a subset of
> xen_has_pv_devices()?

I wish, this thing drives me nuts and I couldn't come up with a sensible
way to make this work for those special ones that have their own
xen_emul_unplug parameter without special casing the
'xen_has_pv_devices'.

Perhaps it should be renamed to 'xen_has_pv_generic_devices' ?

> David