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Re: [Xen-devel] [PATCH] include/public/memory.h: remove the XENMEM_rsrc_acq_caller_owned flag
- To: Jan Beulich <JBeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Fri, 19 Jul 2019 14:42:04 +0100
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, WeiLiu <wl@xxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, Paul Durrant <paul.durrant@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 19 Jul 2019 13:42:13 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 19/07/2019 14:31, Jan Beulich wrote:
> 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.
Oh - even better. I'd not spotted that.
~Andrew
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