Re: [Xen-devel] [PATCH] include/public/memory.h: remove the XENMEM_rsrc_acq_caller_owned flag

[Jan Beulich <JBeulich@xxxxxxxx>]

On 19.07.2019 14:41, Andrew Cooper wrote:
> On 19/07/2019 13:25, Paul Durrant wrote:
>> When commit 3f8f1228 "x86/mm: add HYPERVISOR_memory_op to acquire guest
>> resources" introduced the concept of directly mapping some guest resources,
>> it was envisaged that the memory for some resources associated with a guest
>> may not actually be assigned to that guest, specifically the IOREQ server
>> resource introduces in commit 6e387461 "x86/hvm/ioreq: add a new mappable
>> resource type...". Such resources were dubbed "caller owned" and resulted
>> in the owned resources" and acquiring them resulted in the
>> XENMEM_rsrc_acq_caller_owned flag being passed back to the caller of the
>> memory op.
>>
>> Unfortunately the implementation led to XSA-276, which was mitigated
>> by commit f6b6ae78 "x86/hvm/ioreq: fix page referencing" and then a related
>> memory accounting problem was worked around by commit e862e6ce
>> "x86/hvm/ioreq: use ref-counted target-assigned shared pages". This latter
>> commit removed the only instance of a "caller owned" resource, but the
>> flag was left in header and checked in one place in the core code.
>> This patch removes that now redundant check and removes the definition of
>> XENMEM_rsrc_acq_caller_owned from the public header. Also, since this was
>> the only flag defined for the XENMEM_acquire_resource memory op, it removes
>> the 'flags' field of struct xen_mem_acquire_resource and replaces it with
>> an equivalently sized 'pad' field.
>>
>> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> 
> This is a modification to a public header, but in this specific case, I
> think it is the correct thing to do.

This is in a large "#if defined(__XEN__) || defined(__XEN_TOOLS__)" section,
and we consider public interface parts in such sections volatile anyway.

Jan
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