From: Varad Gautam <vrd@amazon.de>
XEN_DOMCTL_destroydomain creates a continuation if domain_kill -ERESTARTS.
In that scenario, it is possible to receive multiple __pirq_guest_unbind
calls for the same pirq from domain_kill, if the pirq has not yet been
removed from the domain's pirq_tree, as:
domain_kill()
-> domain_relinquish_resources()
-> pci_release_devices()
-> pci_clean_dpci_irq()
-> pirq_guest_unbind()
-> __pirq_guest_unbind()
For a shared pirq (nr_guests > 1), the first call would zap the current
domain from the pirq's guests[] list, but the action handler is never freed
as there are other guests using this pirq. As a result, on the second call,
__pirq_guest_unbind searches for the current domain which has been removed
from the guests[] list, and hits a BUG_ON.
Make __pirq_guest_unbind safe to be called multiple times by letting xen
continue if a shared pirq has already been unbound from this guest. The
PIRQ will be cleaned up from the domain's pirq_tree during the destruction
in complete_domain_destroy anyway.
Signed-off-by: Varad Gautam <vrd@amazon.de>
[taking over from Varad at v4]
Signed-off-by: Paul Durrant <paul@xen.org>
---
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Julien Grall <julien@xen.org>
Cc: Roger Pau Monné <roger.pau@citrix.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Roger suggested cleaning the entry from the domain pirq_tree so that
we need not make it safe to re-call __pirq_guest_unbind(). This seems like
a reasonable suggestion but the semantics of the code are almost
impenetrable (e.g. 'pirq' is used to mean an index, a pointer and is also
the name of struct so you generally have little idea what it actally means)
so I prefer to stick with a small fix that I can actually reason about.
v5:
- BUG_ON(!shareable) rather than ASSERT(shareable)
- Drop ASSERT on nr_guests
v4:
- Re-work the guest array search to make it clearer
v3:
- Style fixups
v2:
- Split the check on action->nr_guests > 0 and make it an ASSERT
---
xen/arch/x86/irq.c | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)
diff --git a/xen/arch/x86/irq.c b/xen/arch/x86/irq.c
index cc2eb8e925..a3701354e6 100644
--- a/xen/arch/x86/irq.c
+++ b/xen/arch/x86/irq.c
@@ -1680,9 +1680,22 @@ static irq_guest_action_t *__pirq_guest_unbind(
BUG_ON(!(desc->status & IRQ_GUEST));
- for ( i = 0; (i < action->nr_guests) && (action->guest[i] != d); i++ )
- continue;
- BUG_ON(i == action->nr_guests);
+ for ( i = 0; i < action->nr_guests; i++ )
+ if ( action->guest[i] == d )
+ break;
+
+ if ( i == action->nr_guests ) /* No matching entry */
+ {
+ /*
+ * In case the pirq was shared, unbound for this domain in an earlier
+ * call, but still existed on the domain's pirq_tree, we still reach
+ * here if there are any later unbind calls on the same pirq. Return
+ * if such an unbind happens.
+ */
+ BUG_ON(!action->shareable);
+ return NULL;
+ }
+
memmove(&action->guest[i], &action->guest[i+1],
(action->nr_guests-i-1) * sizeof(action->guest[0]));
action->nr_guests--;
--
2.20.1
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On 10.03.2020 13:43, paul@xen.org wrote: > v5: > - BUG_ON(!shareable) rather than ASSERT(shareable) > - Drop ASSERT on nr_guests Why drop, rather than move ... > --- a/xen/arch/x86/irq.c > +++ b/xen/arch/x86/irq.c > @@ -1680,9 +1680,22 @@ static irq_guest_action_t *__pirq_guest_unbind( > > BUG_ON(!(desc->status & IRQ_GUEST)); > > - for ( i = 0; (i < action->nr_guests) && (action->guest[i] != d); i++ ) > - continue; > - BUG_ON(i == action->nr_guests); > + for ( i = 0; i < action->nr_guests; i++ ) > + if ( action->guest[i] == d ) > + break; > + > + if ( i == action->nr_guests ) /* No matching entry */ > + { ... back here? (This would be easy enough to take care of while committing, iff we decided to go with this variant.) Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
> -----Original Message----- > From: Jan Beulich <jbeulich@suse.com> > Sent: 10 March 2020 13:57 > To: paul@xen.org > Cc: xen-devel@lists.xenproject.org; Varad Gautam <vrd@amazon.de>; Julien Grall <julien@xen.org>; Roger > Pau Monné <roger.pau@citrix.com>; Andrew Cooper <andrew.cooper3@citrix.com> > Subject: Re: [PATCH v5] x86: irq: Do not BUG_ON multiple unbind calls for shared pirqs > > On 10.03.2020 13:43, paul@xen.org wrote: > > v5: > > - BUG_ON(!shareable) rather than ASSERT(shareable) > > - Drop ASSERT on nr_guests > > Why drop, rather than move ... > > > --- a/xen/arch/x86/irq.c > > +++ b/xen/arch/x86/irq.c > > @@ -1680,9 +1680,22 @@ static irq_guest_action_t *__pirq_guest_unbind( > > > > BUG_ON(!(desc->status & IRQ_GUEST)); > > > > - for ( i = 0; (i < action->nr_guests) && (action->guest[i] != d); i++ ) > > - continue; > > - BUG_ON(i == action->nr_guests); > > + for ( i = 0; i < action->nr_guests; i++ ) > > + if ( action->guest[i] == d ) > > + break; > > + > > + if ( i == action->nr_guests ) /* No matching entry */ > > + { > > ... back here? (This would be easy enough to take care of while > committing, iff we decided to go with this variant.) Ok, let's see how your alternative goes. Paul > > Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
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