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Re: [PATCH for-4.17?] x86/paging: return -EINVAL for paging domctls for dying domains
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- Date: Wed, 9 Nov 2022 16:11:06 +0000
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- Cc: "Henry.Wang@xxxxxxx" <Henry.Wang@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Edwin Torok <edvin.torok@xxxxxxxxxx>
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- Thread-topic: [PATCH for-4.17?] x86/paging: return -EINVAL for paging domctls for dying domains
On 08/11/2022 11:38, Roger Pau Monne wrote:
> Like on the Arm side, return -EINVAL when attempting to do a p2m
> operation on dying domains.
Honestly, I'd drop the comment about ARM. "the Arm side" has existed
for of all of a couple of weeks.
A far better justification is because almost all other DOMCTLs are
rejected with -EINVAL against dying domains.
> The current logic returns 0 and leaves the domctl parameter
> uninitialized for any parameter fetching operations (like the
> GET_ALLOCATION operation), which is not helpful from a toolstack point
> of view, because there's no indication that the data hasn't been
> fetched.
>
> Reported-by: Edwin Török <edvin.torok@xxxxxxxxxx>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, ideally with a
modified commit message.
Xen's behaviour is definitely bogus, whatever the perceived intention
behind this change was originally.
System-wide memory handling is unusably broken for known reasons, let
alone unexpected surprises like this, it is not credible to suggest that
unspecified obsolete code might be broken by such a change; it's
definitely broken, and what we risk is exposing a previously hidden error.
Not that this is relevant, because Xend only makes this hypercall
bounded by domctls which do yield -EINVAL for dying domains.
~Andrew
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