This fixes some inaccuracies in the state machine for the virtualized
ICP when implementing the H_IPI hcall (Set_MFFR and related states):
1. The old code wipes out any pending interrupts when the new MFRR is
more favored than the CPPR but less favored than a pending
interrupt (by always modifying xisr and the pending_pri). This can
cause us to lose a pending external interrupt.
The correct code here is to only modify the pending_pri and xisr in
the ICP if the MFRR is equal to or more favored than the current
pending pri (since in this case, it is guaranteed that that there
cannot be a pending external interrupt). The code changes are
required in both kvmppc_rm_h_ipi and kvmppc_h_ipi.
2. Again, in both kvmppc_rm_h_ipi and kvmppc_h_ipi, there is a check
for whether MFRR is being made less favored AND further if new MFFR
is also less favored than the current CPPR, we check for any
resends pending in the ICP. These checks look like they are
designed to cover the case where if the MFRR is being made less
favored, we opportunistically trigger a resend of any interrupts
that had been previously rejected. Although, this is not a state
described by PAPR, this is an action we actually need to do
especially if the CPPR is already at 0xFF. Because in this case,
the resend bit will stay on until another ICP state change which
may be a long time coming and the interrupt stays pending until
then. The current code which checks for MFRR < CPPR is broken when
CPPR is 0xFF since it will not get triggered in that case.
Ideally, we would want to do a resend only if
prio(pending_interrupt) < mfrr && prio(pending_interrupt) < cppr
where pending interrupt is the one that was rejected. But we don't
have the priority of the pending interrupt state saved, so we
simply trigger a resend whenever the MFRR is made less favored.
3. In kvmppc_rm_h_ipi, where we save state to pass resends to the
virtual mode, we also need to save the ICP whose need_resend we
reset since this does not need to be my ICP (vcpu->arch.icp) as is
incorrectly assumed by the current code. A new field rm_resend_icp
is added to the kvmppc_icp structure for this purpose.
Signed-off-by: Suresh Warrier <warrier@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>
5b88cda665