[xen staging-4.16] pci: fail device assignment if phantom functions cannot be assigned

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commit e481fc9f32339ebf9ddd171a3995a3e44527d148
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Tue Jan 30 14:42:41 2024 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jan 30 14:42:41 2024 +0100

    pci: fail device assignment if phantom functions cannot be assigned
    
    The current behavior is that no error is reported if (some) phantom 
functions
    fail to be assigned during device add or assignment, so the operation 
succeeds
    even if some phantom functions are not correctly setup.
    
    This can lead to devices possibly being successfully assigned to a domU 
while
    some of the device phantom functions are still assigned to dom0.  Even when 
the
    device is assigned domIO before being assigned to a domU phantom functions
    might fail to be assigned to domIO, and also fail to be assigned to the 
domU,
    leaving them assigned to dom0.
    
    Since the device can generate requests using the IDs of those phantom
    functions, given the scenario above a device in such state would be in 
control
    of a domU, but still capable of generating transactions that use a context 
ID
    targeting dom0 owned memory.
    
    Modify device assign in order to attempt to deassign the device if phantom
    functions failed to be assigned.
    
    Note that device addition is not modified in the same way, as in that case 
the
    device is assigned to a trusted domain, and hence partial assign can lead to
    device malfunction but not a security issue.
    
    This is XSA-449 / CVE-2023-46839
    
    Fixes: 4e9950dc1bd2 ('IOMMU: add phantom function support')
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: cb4ecb3cc17b02c2814bc817efd05f3f3ba33d1e
    master date: 2024-01-30 14:28:01 +0100
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