Re: [Xen-devel] [PATCH 2/2] x86/livepatch: Prevent patching with active waitqueues

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

On 11/5/19 7:43 PM, Andrew Cooper wrote:
> The safety of livepatching depends on every stack having been unwound, but
> there is one corner case where this is not true.  The Sharing/Paging/Monitor
> infrastructure may use waitqueues, which copy the stack frame sideways and
> longjmp() to a different vcpu.
> 
> This case is rare, and can be worked around by pausing the offending
> domain(s), waiting for their rings to drain, then performing a livepatch.
> 
> In the case that there is an active waitqueue, fail the livepatch attempt with
> -EBUSY, which is preforable to the fireworks which occur from trying to unwind
> the old stack frame at a later point.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>

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