Re: [Xen-devel] [PATCH 2/7] vm-event: VM_EVENT_FLAG_DENY requires VM_EVENT_FLAG_VCPU_PAUSED

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Thu, Jun 16, 2016 at 8:07 AM, Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx> wrote:
> For VM_EVENT_FLAG_DENY to work, the vcpu must be paused (sync = 1) until the
> vm-event is handled. A vm-event response having VM_EVENT_FLAG_DENY flag set
> should also set the VM_EVENT_FLAG_VCPU_PAUSED flag. Enforce that in
> vm_event_register_write_resume().

Well, the problem with this is that the user can set the VCPU_PAUSED
flag any time it wants. It can happen that Xen hasn't paused the vCPU
but the user still sends that flag, in which case the unpause the flag
induces will not actually do anything. You should also check if the
vCPU is in fact paused rather then just relying on this flag.

Tamas

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