[xen staging] x86/pass-through: defer event unlock in pt_irq_create_bind()

[patchbot@xxxxxxx]

commit 62dbde7a7965f339b5aa90daeeb437f12c6b97d2
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Wed Sep 23 09:02:29 2026 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Sep 23 10:01:38 2026 +0200

    x86/pass-through: defer event unlock in pt_irq_create_bind()
    
    The radix tree holding struct pirq * as obtained by pirq_get_info() is
    protected by the domain's event lock. The result ("info") and the derived
    "pirq_dpci" therefore may not be de-referenced past the dropping of that
    lock. Moving the unlock down is safe, but perhaps not obviously so:
    - vector_hashing_dest() does a memory allocation, but core event channel
      code does so too while holding the lock; the call to
      vlapic_match_dest() doesn't involve any further locking,
    - hvm_migrate_pirq() operates on the corresponding IRQ descriptor, where
      obtaining of its lock is of course fine (those locks always nest inside
      the event lock),
    - {hvm,vmx}_pi_update_irte() are very similar to hvm_migrate_pirq()
      locking-wise,
    - the locking around guest_mask_msi_irq() is the same as in the earlier
      two bullet points.
    
    As long as the PCI-devs lock is held around both
    pt_irq_{create,destroy}_bind(), this is only a latent issue.
    
    Fixes: 35a1caf8b6b5 ("pass-through: update IRTE according to guest 
interrupt config changes")
    Fixes: 1066331913c9 ("passthrough: don't migrate pirq when it is delivered 
through VT-d PI")
    Fixes: 782cf8ba4678 ("pass-through: adjust pIRQ migration")
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Roger Pau Monné <roger@xxxxxxxxxxxxxx>
---
 xen/drivers/passthrough/x86/hvm.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/xen/drivers/passthrough/x86/hvm.c 
b/xen/drivers/passthrough/x86/hvm.c
index 32632a3b15..67486b99bd 100644
--- a/xen/drivers/passthrough/x86/hvm.c
+++ b/xen/drivers/passthrough/x86/hvm.c
@@ -371,7 +371,6 @@ int pt_irq_create_bind(
 
         dest_vcpu_id = hvm_girq_dest_2_vcpu_id(d, dest, dest_mode);
         pirq_dpci->gmsi.dest_vcpu_id = dest_vcpu_id;
-        write_unlock(&d->event_lock);
 
         pirq_dpci->gmsi.posted = false;
         vcpu = (dest_vcpu_id >= 0) ? d->vcpu[dest_vcpu_id] : NULL;
@@ -393,6 +392,7 @@ int pt_irq_create_bind(
 
             if ( rc )
             {
+                write_unlock(&d->event_lock);
                 pt_irq_destroy_bind(d, pt_irq_bind);
                 return rc;
             }
@@ -405,6 +405,7 @@ int pt_irq_create_bind(
 
             if ( !desc )
             {
+                write_unlock(&d->event_lock);
                 pt_irq_destroy_bind(d, pt_irq_bind);
                 return -EINVAL;
             }
@@ -413,6 +414,7 @@ int pt_irq_create_bind(
             spin_unlock_irqrestore(&desc->lock, flags);
         }
 
+        write_unlock(&d->event_lock);
         break;
     }
 
--
generated by git-patchbot for /home/xen/git/xen.git#staging