[xen staging] pci: fix locking around vPCI removal in pci_remove_device()

[patchbot@xxxxxxx]

commit 635dd1120a01961a39dce6ad3f09692681379378
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Thu Feb 29 17:00:40 2024 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Feb 29 17:00:40 2024 +0100

    pci: fix locking around vPCI removal in pci_remove_device()
    
    Currently vpci_deassign_device() is called without holding the per-domain
    pci_lock in pci_remove_device(), which leads to:
    
    Assertion 'rw_is_write_locked(&pdev->domain->pci_lock)' failed at 
../drivers/vpci/vpci.c:47
    [...]
    Xen call trace:
       [<ffff82d040260eac>] R vpci_deassign_device+0x10d/0x1b9
       [<ffff82d04027932f>] S pci_remove_device+0x2b1/0x380
       [<ffff82d040260bd0>] F pci_physdev_op+0x197/0x19e
       [<ffff82d04032272d>] F do_physdev_op+0x342/0x12aa
       [<ffff82d0402f067a>] F pv_hypercall+0x58e/0x62b
       [<ffff82d0402012ba>] F lstar_enter+0x13a/0x140
    
    Move the existing block that removes the device from the domain pdev_list 
ahead
    and also issue the call to vpci_deassign_device() there.  It's fine to 
remove
    the device from the domain list of assigned devices, as further functions 
only
    care that the pdev domain field is correctly set to the owner of the device
    about to be removed.
    
    Moving the vpci_deassign_device() past the pci_cleanup_msi() call can be
    dangerous, as doing the MSI cleanup ahead of having removed the vPCI 
handlers
    could lead to stale data in vPCI MSI(-X) internal structures.
    
    Fixes: 4f78438b45e2 ('vpci: use per-domain PCI lock to protect vpci 
structure')
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
---
 xen/drivers/passthrough/pci.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/xen/drivers/passthrough/pci.c b/xen/drivers/passthrough/pci.c
index 4c0a836486..194701c913 100644
--- a/xen/drivers/passthrough/pci.c
+++ b/xen/drivers/passthrough/pci.c
@@ -817,15 +817,15 @@ int pci_remove_device(u16 seg, u8 bus, u8 devfn)
     list_for_each_entry ( pdev, &pseg->alldevs_list, alldevs_list )
         if ( pdev->bus == bus && pdev->devfn == devfn )
         {
-            vpci_deassign_device(pdev);
-            pci_cleanup_msi(pdev);
-            ret = iommu_remove_device(pdev);
             if ( pdev->domain )
             {
                 write_lock(&pdev->domain->pci_lock);
+                vpci_deassign_device(pdev);
                 list_del(&pdev->domain_list);
                 write_unlock(&pdev->domain->pci_lock);
             }
+            pci_cleanup_msi(pdev);
+            ret = iommu_remove_device(pdev);
             printk(XENLOG_DEBUG "PCI remove device %pp\n", &pdev->sbdf);
             free_pdev(pseg, pdev);
             break;
--
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