linux-stable.git/drivers/xen, branch linux-6.5.y Linux kernel stable tree xen/events: fix delayed eoi list handling 2023-11-28T17:14:55+00:00 Juergen Gross jgross@suse.com 2023-09-25T15:54:13+00:00 36fcea86f71d10e5b05537fb742dd8c7ea7a3ac0 [ Upstream commit 47d970204054f859f35a2237baa75c2d84fcf436 ] When delaying eoi handling of events, the related elements are queued into the percpu lateeoi list. In case the list isn't empty, the elements should be sorted by the time when eoi handling is to happen. Unfortunately a new element will never be queued at the start of the list, even if it has a handling time lower than all other list elements. Fix that by handling that case the same way as for an empty list. Fixes: e99502f76271 ("xen/events: defer eoi in case of excessive number of events") Reported-by: Jan Beulich <jbeulich@suse.com> Signed-off-by: Juergen Gross <jgross@suse.com> Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> Signed-off-by: Juergen Gross <jgross@suse.com> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 47d970204054f859f35a2237baa75c2d84fcf436 ]

When delaying eoi handling of events, the related elements are queued
into the percpu lateeoi list. In case the list isn't empty, the
elements should be sorted by the time when eoi handling is to happen.

Unfortunately a new element will never be queued at the start of the
list, even if it has a handling time lower than all other list
elements.

Fix that by handling that case the same way as for an empty list.

Fixes: e99502f76271 ("xen/events: defer eoi in case of excessive number of events")
Reported-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
xen/events: avoid using info_for_irq() in xen_send_IPI_one() 2023-11-28T17:14:54+00:00 Juergen Gross jgross@suse.com 2023-10-24T11:51:36+00:00 0ad883132835167457292f782ba957bdb4ff0972 [ Upstream commit e64e7c74b99ec9e439abca75f522f4b98f220bd1 ] xen_send_IPI_one() is being used by cpuhp_report_idle_dead() after it calls rcu_report_dead(), meaning that any RCU usage by xen_send_IPI_one() is a bad idea. Unfortunately xen_send_IPI_one() is using notify_remote_via_irq() today, which is using irq_get_chip_data() via info_for_irq(). And irq_get_chip_data() in turn is using a maple-tree lookup requiring RCU. Avoid this problem by caching the ipi event channels in another percpu variable, allowing the use notify_remote_via_evtchn() in xen_send_IPI_one(). Fixes: 721255b9826b ("genirq: Use a maple tree for interrupt descriptor management") Reported-by: David Woodhouse <dwmw@amazon.co.uk> Signed-off-by: Juergen Gross <jgross@suse.com> Tested-by: David Woodhouse <dwmw@amazon.co.uk> Acked-by: Stefano Stabellini <sstabellini@kernel.org> Signed-off-by: Juergen Gross <jgross@suse.com> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit e64e7c74b99ec9e439abca75f522f4b98f220bd1 ]

xen_send_IPI_one() is being used by cpuhp_report_idle_dead() after
it calls rcu_report_dead(), meaning that any RCU usage by
xen_send_IPI_one() is a bad idea.

Unfortunately xen_send_IPI_one() is using notify_remote_via_irq()
today, which is using irq_get_chip_data() via info_for_irq(). And
irq_get_chip_data() in turn is using a maple-tree lookup requiring
RCU.

Avoid this problem by caching the ipi event channels in another
percpu variable, allowing the use notify_remote_via_evtchn() in
xen_send_IPI_one().

Fixes: 721255b9826b ("genirq: Use a maple tree for interrupt descriptor management")
Reported-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Juergen Gross <jgross@suse.com>
Tested-by: David Woodhouse <dwmw@amazon.co.uk>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
xen-pciback: Consider INTx disabled when MSI/MSI-X is enabled 2023-11-20T10:57:02+00:00 Marek Marczykowski-Górecki marmarek@invisiblethingslab.com 2023-10-16T13:13:25+00:00 2a57291a1131a15efa3e0dd1dd66721da324dd79 [ Upstream commit 2c269f42d0f382743ab230308b836ffe5ae9b2ae ] Linux enables MSI-X before disabling INTx, but keeps MSI-X masked until the table is filled. Then it disables INTx just before clearing MASKALL bit. Currently this approach is rejected by xen-pciback. According to the PCIe spec, device cannot use INTx when MSI/MSI-X is enabled (in other words: enabling MSI/MSI-X implicitly disables INTx). Change the logic to consider INTx disabled if MSI/MSI-X is enabled. This applies to three places: - checking currently enabled interrupts type, - transition to MSI/MSI-X - where INTx would be implicitly disabled, - clearing INTx disable bit - which can be allowed even if MSI/MSI-X is enabled, as device should consider INTx disabled anyway in that case Fixes: 5e29500eba2a ("xen-pciback: Allow setting PCI_MSIX_FLAGS_MASKALL too") Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com> Acked-by: Juergen Gross <jgross@suse.com> Link: https://lore.kernel.org/r/20231016131348.1734721-1-marmarek@invisiblethingslab.com Signed-off-by: Juergen Gross <jgross@suse.com> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 2c269f42d0f382743ab230308b836ffe5ae9b2ae ]

Linux enables MSI-X before disabling INTx, but keeps MSI-X masked until
the table is filled. Then it disables INTx just before clearing MASKALL
bit. Currently this approach is rejected by xen-pciback.
According to the PCIe spec, device cannot use INTx when MSI/MSI-X is
enabled (in other words: enabling MSI/MSI-X implicitly disables INTx).

Change the logic to consider INTx disabled if MSI/MSI-X is enabled. This
applies to three places:
 - checking currently enabled interrupts type,
 - transition to MSI/MSI-X - where INTx would be implicitly disabled,
 - clearing INTx disable bit - which can be allowed even if MSI/MSI-X is
   enabled, as device should consider INTx disabled anyway in that case

Fixes: 5e29500eba2a ("xen-pciback: Allow setting PCI_MSIX_FLAGS_MASKALL too")
Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Acked-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20231016131348.1734721-1-marmarek@invisiblethingslab.com
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
xenbus: fix error exit in xenbus_init() 2023-11-20T10:57:02+00:00 Juergen Gross jgross@suse.com 2023-08-22T09:11:38+00:00 ce60d6cc40fdc9581c49b571b05ccbe8aeff9eef [ Upstream commit 44961b81a9e9059b5c0443643915386db7035227 ] In case an error occurs in xenbus_init(), xen_store_domain_type should be set to XS_UNKNOWN. Fix one instance where this action is missing. Fixes: 5b3353949e89 ("xen: add support for initializing xenstore later as HVM domain") Reported-by: kernel test robot <lkp@intel.com> Reported-by: Dan Carpenter <error27@gmail.com> Link: https://lore.kernel.org/r/202304200845.w7m4kXZr-lkp@intel.com/ Signed-off-by: Juergen Gross <jgross@suse.com> Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> Link: https://lore.kernel.org/r/20230822091138.4765-1-jgross@suse.com Signed-off-by: Juergen Gross <jgross@suse.com> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 44961b81a9e9059b5c0443643915386db7035227 ]

In case an error occurs in xenbus_init(), xen_store_domain_type should
be set to XS_UNKNOWN.

Fix one instance where this action is missing.

Fixes: 5b3353949e89 ("xen: add support for initializing xenstore later as HVM domain")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <error27@gmail.com>
Link: https://lore.kernel.org/r/202304200845.w7m4kXZr-lkp@intel.com/
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Link: https://lore.kernel.org/r/20230822091138.4765-1-jgross@suse.com
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
xen/events: replace evtchn_rwlock with RCU 2023-10-10T20:03:06+00:00 Juergen Gross jgross@suse.com 2023-08-28T06:09:47+00:00 76b33722e2d2336a6e2a7d9eacbbb8988478cf98 commit 87797fad6cce28ec9be3c13f031776ff4f104cfc upstream. In unprivileged Xen guests event handling can cause a deadlock with Xen console handling. The evtchn_rwlock and the hvc_lock are taken in opposite sequence in __hvc_poll() and in Xen console IRQ handling. Normally this is no problem, as the evtchn_rwlock is taken as a reader in both paths, but as soon as an event channel is being closed, the lock will be taken as a writer, which will cause read_lock() to block: CPU0 CPU1 CPU2 (IRQ handling) (__hvc_poll()) (closing event channel) read_lock(evtchn_rwlock) spin_lock(hvc_lock) write_lock(evtchn_rwlock) [blocks] spin_lock(hvc_lock) [blocks] read_lock(evtchn_rwlock) [blocks due to writer waiting, and not in_interrupt()] This issue can be avoided by replacing evtchn_rwlock with RCU in xen_free_irq(). Note that RCU is used only to delay freeing of the irq_info memory. There is no RCU based dereferencing or replacement of pointers involved. In order to avoid potential races between removing the irq_info reference and handling of interrupts, set the irq_info pointer to NULL only when freeing its memory. The IRQ itself must be freed at that time, too, as otherwise the same IRQ number could be allocated again before handling of the old instance would have been finished. This is XSA-441 / CVE-2023-34324. Fixes: 54c9de89895e ("xen/events: add a new "late EOI" evtchn framework") Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com> Signed-off-by: Juergen Gross <jgross@suse.com> Reviewed-by: Julien Grall <jgrall@amazon.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 87797fad6cce28ec9be3c13f031776ff4f104cfc upstream.

In unprivileged Xen guests event handling can cause a deadlock with
Xen console handling. The evtchn_rwlock and the hvc_lock are taken in
opposite sequence in __hvc_poll() and in Xen console IRQ handling.
Normally this is no problem, as the evtchn_rwlock is taken as a reader
in both paths, but as soon as an event channel is being closed, the
lock will be taken as a writer, which will cause read_lock() to block:

CPU0                     CPU1                CPU2
(IRQ handling)           (__hvc_poll())      (closing event channel)

read_lock(evtchn_rwlock)
                         spin_lock(hvc_lock)
                                             write_lock(evtchn_rwlock)
                                                 [blocks]
spin_lock(hvc_lock)
    [blocks]
                        read_lock(evtchn_rwlock)
                            [blocks due to writer waiting,
                             and not in_interrupt()]

This issue can be avoided by replacing evtchn_rwlock with RCU in
xen_free_irq(). Note that RCU is used only to delay freeing of the
irq_info memory. There is no RCU based dereferencing or replacement of
pointers involved.

In order to avoid potential races between removing the irq_info
reference and handling of interrupts, set the irq_info pointer to NULL
only when freeing its memory. The IRQ itself must be freed at that
time, too, as otherwise the same IRQ number could be allocated again
before handling of the old instance would have been finished.

This is XSA-441 / CVE-2023-34324.

Fixes: 54c9de89895e ("xen/events: add a new "late EOI" evtchn framework")
Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
xen: speed up grant-table reclaim 2023-07-27T05:53:12+00:00 Demi Marie Obenour demi@invisiblethingslab.com 2023-07-26T16:52:41+00:00 c04e9894846c663f3278a414f34416e6e45bbe68 When a grant entry is still in use by the remote domain, Linux must put it on a deferred list. Normally, this list is very short, because the PV network and block protocols expect the backend to unmap the grant first. However, Qubes OS's GUI protocol is subject to the constraints of the X Window System, and as such winds up with the frontend unmapping the window first. As a result, the list can grow very large, resulting in a massive memory leak and eventual VM freeze. To partially solve this problem, make the number of entries that the VM will attempt to free at each iteration tunable. The default is still 10, but it can be overridden via a module parameter. This is Cc: stable because (when combined with appropriate userspace changes) it fixes a severe performance and stability problem for Qubes OS users. Cc: stable@vger.kernel.org Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com> Reviewed-by: Juergen Gross <jgross@suse.com> Link: https://lore.kernel.org/r/20230726165354.1252-1-demi@invisiblethingslab.com Signed-off-by: Juergen Gross <jgross@suse.com> 
When a grant entry is still in use by the remote domain, Linux must put
it on a deferred list.  Normally, this list is very short, because
the PV network and block protocols expect the backend to unmap the grant
first.  However, Qubes OS's GUI protocol is subject to the constraints
of the X Window System, and as such winds up with the frontend unmapping
the window first.  As a result, the list can grow very large, resulting
in a massive memory leak and eventual VM freeze.

To partially solve this problem, make the number of entries that the VM
will attempt to free at each iteration tunable.  The default is still
10, but it can be overridden via a module parameter.

This is Cc: stable because (when combined with appropriate userspace
changes) it fixes a severe performance and stability problem for Qubes
OS users.

Cc: stable@vger.kernel.org
Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20230726165354.1252-1-demi@invisiblethingslab.com
Signed-off-by: Juergen Gross <jgross@suse.com>
xen/evtchn: Introduce new IOCTL to bind static evtchn 2023-07-26T06:42:34+00:00 Rahul Singh rahul.singh@arm.com 2023-07-18T11:31:07+00:00 58f6259b7a08f8d47d4629609703d358b042f0fd Xen 4.17 supports the creation of static evtchns. To allow user space application to bind static evtchns introduce new ioctl "IOCTL_EVTCHN_BIND_STATIC". Existing IOCTL doing more than binding that’s why we need to introduce the new IOCTL to only bind the static event channels. Static evtchns to be available for use during the lifetime of the guest. When the application exits, __unbind_from_irq() ends up being called from release() file operations because of that static evtchns are getting closed. To avoid closing the static event channel, add the new bool variable "is_static" in "struct irq_info" to mark the event channel static when creating the event channel to avoid closing the static evtchn. Also, take this opportunity to remove the open-coded version of the evtchn close in drivers/xen/evtchn.c file and use xen_evtchn_close(). Signed-off-by: Rahul Singh <rahul.singh@arm.com> Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> Acked-by: Stefano Stabellini <sstabellini@kernel.org> Link: https://lore.kernel.org/r/ae7329bf1713f83e4aad4f3fa0f316258c40a3e9.1689677042.git.rahul.singh@arm.com Signed-off-by: Juergen Gross <jgross@suse.com> 
Xen 4.17 supports the creation of static evtchns. To allow user space
application to bind static evtchns introduce new ioctl
"IOCTL_EVTCHN_BIND_STATIC". Existing IOCTL doing more than binding
that’s why we need to introduce the new IOCTL to only bind the static
event channels.

Static evtchns to be available for use during the lifetime of the
guest. When the application exits, __unbind_from_irq() ends up being
called from release() file operations because of that static evtchns
are getting closed. To avoid closing the static event channel, add the
new bool variable "is_static" in "struct irq_info" to mark the event
channel static when creating the event channel to avoid closing the
static evtchn.

Also, take this opportunity to remove the open-coded version of the
evtchn close in drivers/xen/evtchn.c file and use xen_evtchn_close().

Signed-off-by: Rahul Singh <rahul.singh@arm.com>
Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Link: https://lore.kernel.org/r/ae7329bf1713f83e4aad4f3fa0f316258c40a3e9.1689677042.git.rahul.singh@arm.com
Signed-off-by: Juergen Gross <jgross@suse.com>
xenbus: check xen_domain in xenbus_probe_initcall 2023-07-25T15:36:36+00:00 Stefano Stabellini sstabellini@kernel.org 2023-07-21T23:13:03+00:00 0d8f7cc8057890db08c54fe610d8a94af59da082 The same way we already do in xenbus_init. Fixes the following warning: [ 352.175563] Trying to free already-free IRQ 0 [ 352.177355] WARNING: CPU: 1 PID: 88 at kernel/irq/manage.c:1893 free_irq+0xbf/0x350 [...] [ 352.213951] Call Trace: [ 352.214390] <TASK> [ 352.214717] ? __warn+0x81/0x170 [ 352.215436] ? free_irq+0xbf/0x350 [ 352.215906] ? report_bug+0x10b/0x200 [ 352.216408] ? prb_read_valid+0x17/0x20 [ 352.216926] ? handle_bug+0x44/0x80 [ 352.217409] ? exc_invalid_op+0x13/0x60 [ 352.217932] ? asm_exc_invalid_op+0x16/0x20 [ 352.218497] ? free_irq+0xbf/0x350 [ 352.218979] ? __pfx_xenbus_probe_thread+0x10/0x10 [ 352.219600] xenbus_probe+0x7a/0x80 [ 352.221030] xenbus_probe_thread+0x76/0xc0 Fixes: 5b3353949e89 ("xen: add support for initializing xenstore later as HVM domain") Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com> Tested-by: Petr Mladek <pmladek@suse.com> Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> Link: https://lore.kernel.org/r/alpine.DEB.2.22.394.2307211609140.3118466@ubuntu-linux-20-04-desktop Signed-off-by: Juergen Gross <jgross@suse.com> 
The same way we already do in xenbus_init.
Fixes the following warning:

[  352.175563] Trying to free already-free IRQ 0
[  352.177355] WARNING: CPU: 1 PID: 88 at kernel/irq/manage.c:1893 free_irq+0xbf/0x350
[...]
[  352.213951] Call Trace:
[  352.214390]  <TASK>
[  352.214717]  ? __warn+0x81/0x170
[  352.215436]  ? free_irq+0xbf/0x350
[  352.215906]  ? report_bug+0x10b/0x200
[  352.216408]  ? prb_read_valid+0x17/0x20
[  352.216926]  ? handle_bug+0x44/0x80
[  352.217409]  ? exc_invalid_op+0x13/0x60
[  352.217932]  ? asm_exc_invalid_op+0x16/0x20
[  352.218497]  ? free_irq+0xbf/0x350
[  352.218979]  ? __pfx_xenbus_probe_thread+0x10/0x10
[  352.219600]  xenbus_probe+0x7a/0x80
[  352.221030]  xenbus_probe_thread+0x76/0xc0

Fixes: 5b3353949e89 ("xen: add support for initializing xenstore later as HVM domain")
Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com>
Tested-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>

Link: https://lore.kernel.org/r/alpine.DEB.2.22.394.2307211609140.3118466@ubuntu-linux-20-04-desktop
Signed-off-by: Juergen Gross <jgross@suse.com>
Merge tag 'for-linus-6.5-rc2-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip 2023-07-13T20:39:36+00:00 Linus Torvalds torvalds@linux-foundation.org 2023-07-13T20:39:36+00:00 15999328946bd778b7bbf57179ee871dd5279b04 Pull xen fixes from Juergen Gross: - a cleanup of the Xen related ELF-notes - a fix for virtio handling in Xen dom0 when running Xen in a VM * tag 'for-linus-6.5-rc2-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip: xen/virtio: Fix NULL deref when a bridge of PCI root bus has no parent x86/Xen: tidy xen-head.S 
Pull xen fixes from Juergen Gross:

 - a cleanup of the Xen related ELF-notes

 - a fix for virtio handling in Xen dom0 when running Xen in a VM

* tag 'for-linus-6.5-rc2-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip:
  xen/virtio: Fix NULL deref when a bridge of PCI root bus has no parent
  x86/Xen: tidy xen-head.S
xen/virtio: Fix NULL deref when a bridge of PCI root bus has no parent 2023-07-04T06:18:21+00:00 Petr Pavlu petr.pavlu@suse.com 2023-06-21T13:12:13+00:00 21a235bce12361e64adfc2ef97e4ae2e51ad63d4 When attempting to run Xen on a QEMU/KVM virtual machine with virtio devices (all x86_64), function xen_dt_get_node() crashes on accessing bus->bridge->parent->of_node because a bridge of the PCI root bus has no parent set: [ 1.694192][ T1] BUG: kernel NULL pointer dereference, address: 0000000000000288 [ 1.695688][ T1] #PF: supervisor read access in kernel mode [ 1.696297][ T1] #PF: error_code(0x0000) - not-present page [ 1.696297][ T1] PGD 0 P4D 0 [ 1.696297][ T1] Oops: 0000 [#1] PREEMPT SMP NOPTI [ 1.696297][ T1] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.3.7-1-default #1 openSUSE Tumbleweed a577eae57964bb7e83477b5a5645a1781df990f0 [ 1.696297][ T1] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.15.0-0-g2dd4b9b-rebuilt.opensuse.org 04/01/2014 [ 1.696297][ T1] RIP: e030:xen_virtio_restricted_mem_acc+0xd9/0x1c0 [ 1.696297][ T1] Code: 45 0c 83 e8 c9 a3 ea ff 31 c0 eb d7 48 8b 87 40 ff ff ff 48 89 c2 48 8b 40 10 48 85 c0 75 f4 48 8b 82 10 01 00 00 48 8b 40 40 <48> 83 b8 88 02 00 00 00 0f 84 45 ff ff ff 66 90 31 c0 eb a5 48 89 [ 1.696297][ T1] RSP: e02b:ffffc90040013cc8 EFLAGS: 00010246 [ 1.696297][ T1] RAX: 0000000000000000 RBX: ffff888006c75000 RCX: 0000000000000029 [ 1.696297][ T1] RDX: ffff888005ed1000 RSI: ffffc900400f100c RDI: ffff888005ee30d0 [ 1.696297][ T1] RBP: ffff888006c75010 R08: 0000000000000001 R09: 0000000330000006 [ 1.696297][ T1] R10: ffff888005850028 R11: 0000000000000002 R12: ffffffff830439a0 [ 1.696297][ T1] R13: 0000000000000000 R14: ffff888005657900 R15: ffff888006e3e1e8 [ 1.696297][ T1] FS: 0000000000000000(0000) GS:ffff88804a000000(0000) knlGS:0000000000000000 [ 1.696297][ T1] CS: e030 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 1.696297][ T1] CR2: 0000000000000288 CR3: 0000000002e36000 CR4: 0000000000050660 [ 1.696297][ T1] Call Trace: [ 1.696297][ T1] <TASK> [ 1.696297][ T1] virtio_features_ok+0x1b/0xd0 [ 1.696297][ T1] virtio_dev_probe+0x19c/0x270 [ 1.696297][ T1] really_probe+0x19b/0x3e0 [ 1.696297][ T1] __driver_probe_device+0x78/0x160 [ 1.696297][ T1] driver_probe_device+0x1f/0x90 [ 1.696297][ T1] __driver_attach+0xd2/0x1c0 [ 1.696297][ T1] bus_for_each_dev+0x74/0xc0 [ 1.696297][ T1] bus_add_driver+0x116/0x220 [ 1.696297][ T1] driver_register+0x59/0x100 [ 1.696297][ T1] virtio_console_init+0x7f/0x110 [ 1.696297][ T1] do_one_initcall+0x47/0x220 [ 1.696297][ T1] kernel_init_freeable+0x328/0x480 [ 1.696297][ T1] kernel_init+0x1a/0x1c0 [ 1.696297][ T1] ret_from_fork+0x29/0x50 [ 1.696297][ T1] </TASK> [ 1.696297][ T1] Modules linked in: [ 1.696297][ T1] CR2: 0000000000000288 [ 1.696297][ T1] ---[ end trace 0000000000000000 ]--- The PCI root bus is in this case created from ACPI description via acpi_pci_root_add() -> pci_acpi_scan_root() -> acpi_pci_root_create() -> pci_create_root_bus() where the last function is called with parent=NULL. It indicates that no parent is present and then bus->bridge->parent is NULL too. Fix the problem by checking bus->bridge->parent in xen_dt_get_node() for NULL first. Fixes: ef8ae384b4c9 ("xen/virtio: Handle PCI devices which Host controller is described in DT") Signed-off-by: Petr Pavlu <petr.pavlu@suse.com> Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> Reviewed-by: Stefano Stabellini <sstabellini@kernel.org> Link: https://lore.kernel.org/r/20230621131214.9398-2-petr.pavlu@suse.com Signed-off-by: Juergen Gross <jgross@suse.com> 
When attempting to run Xen on a QEMU/KVM virtual machine with virtio
devices (all x86_64), function xen_dt_get_node() crashes on accessing
bus->bridge->parent->of_node because a bridge of the PCI root bus has no
parent set:

[    1.694192][    T1] BUG: kernel NULL pointer dereference, address: 0000000000000288
[    1.695688][    T1] #PF: supervisor read access in kernel mode
[    1.696297][    T1] #PF: error_code(0x0000) - not-present page
[    1.696297][    T1] PGD 0 P4D 0
[    1.696297][    T1] Oops: 0000 [#1] PREEMPT SMP NOPTI
[    1.696297][    T1] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.3.7-1-default #1 openSUSE Tumbleweed a577eae57964bb7e83477b5a5645a1781df990f0
[    1.696297][    T1] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.15.0-0-g2dd4b9b-rebuilt.opensuse.org 04/01/2014
[    1.696297][    T1] RIP: e030:xen_virtio_restricted_mem_acc+0xd9/0x1c0
[    1.696297][    T1] Code: 45 0c 83 e8 c9 a3 ea ff 31 c0 eb d7 48 8b 87 40 ff ff ff 48 89 c2 48 8b 40 10 48 85 c0 75 f4 48 8b 82 10 01 00 00 48 8b 40 40 <48> 83 b8 88 02 00 00 00 0f 84 45 ff ff ff 66 90 31 c0 eb a5 48 89
[    1.696297][    T1] RSP: e02b:ffffc90040013cc8 EFLAGS: 00010246
[    1.696297][    T1] RAX: 0000000000000000 RBX: ffff888006c75000 RCX: 0000000000000029
[    1.696297][    T1] RDX: ffff888005ed1000 RSI: ffffc900400f100c RDI: ffff888005ee30d0
[    1.696297][    T1] RBP: ffff888006c75010 R08: 0000000000000001 R09: 0000000330000006
[    1.696297][    T1] R10: ffff888005850028 R11: 0000000000000002 R12: ffffffff830439a0
[    1.696297][    T1] R13: 0000000000000000 R14: ffff888005657900 R15: ffff888006e3e1e8
[    1.696297][    T1] FS:  0000000000000000(0000) GS:ffff88804a000000(0000) knlGS:0000000000000000
[    1.696297][    T1] CS:  e030 DS: 0000 ES: 0000 CR0: 0000000080050033
[    1.696297][    T1] CR2: 0000000000000288 CR3: 0000000002e36000 CR4: 0000000000050660
[    1.696297][    T1] Call Trace:
[    1.696297][    T1]  <TASK>
[    1.696297][    T1]  virtio_features_ok+0x1b/0xd0
[    1.696297][    T1]  virtio_dev_probe+0x19c/0x270
[    1.696297][    T1]  really_probe+0x19b/0x3e0
[    1.696297][    T1]  __driver_probe_device+0x78/0x160
[    1.696297][    T1]  driver_probe_device+0x1f/0x90
[    1.696297][    T1]  __driver_attach+0xd2/0x1c0
[    1.696297][    T1]  bus_for_each_dev+0x74/0xc0
[    1.696297][    T1]  bus_add_driver+0x116/0x220
[    1.696297][    T1]  driver_register+0x59/0x100
[    1.696297][    T1]  virtio_console_init+0x7f/0x110
[    1.696297][    T1]  do_one_initcall+0x47/0x220
[    1.696297][    T1]  kernel_init_freeable+0x328/0x480
[    1.696297][    T1]  kernel_init+0x1a/0x1c0
[    1.696297][    T1]  ret_from_fork+0x29/0x50
[    1.696297][    T1]  </TASK>
[    1.696297][    T1] Modules linked in:
[    1.696297][    T1] CR2: 0000000000000288
[    1.696297][    T1] ---[ end trace 0000000000000000 ]---

The PCI root bus is in this case created from ACPI description via
acpi_pci_root_add() -> pci_acpi_scan_root() -> acpi_pci_root_create() ->
pci_create_root_bus() where the last function is called with
parent=NULL. It indicates that no parent is present and then
bus->bridge->parent is NULL too.

Fix the problem by checking bus->bridge->parent in xen_dt_get_node() for
NULL first.

Fixes: ef8ae384b4c9 ("xen/virtio: Handle PCI devices which Host controller is described in DT")
Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Link: https://lore.kernel.org/r/20230621131214.9398-2-petr.pavlu@suse.com
Signed-off-by: Juergen Gross <jgross@suse.com>