In some cases, ibm,client-architecture-support calls can fail. This
could happen in the current code for situations where the modified
device tree segment exceeds the buffer size provided by the guest
via the call parameters. In these cases, QEMU will reset, allowing
an opportunity to regenerate the device tree from scratch via
boot-time handling. There are potentially other scenarios as well,
not currently reachable in the current code, but possible in theory,
such as cases where device-tree properties or nodes need to be removed.
We currently don't handle either of these properly for option vector
capabilities however. Instead of carrying the negotiated capability
beyond the reset and creating the boot-time device tree accordingly,
we start from scratch, generating the same boot-time device tree as we
did prior to the CAS-generated and the same device tree updates as we
did before. This could (in theory) cause us to get stuck in a reset
loop. This hasn't been observed, but depending on the extensiveness
of CAS-induced device tree updates in the future, could eventually
become an issue.
Address this by pulling capability-related device tree
updates resulting from CAS calls into a common routine,
spapr_dt_cas_updates(), and adding an sPAPROptionVector*
parameter that allows us to test for newly-negotiated capabilities.
We invoke it as follows:
1) When ibm,client-architecture-support gets called, we
call spapr_dt_cas_updates() with the set of capabilities
added since the previous call to ibm,client-architecture-support.
For the initial boot, or a system reset generated by something
other than the CAS call itself, this set will consist of *all*
options supported both the platform and the guest. For calls
to ibm,client-architecture-support immediately after a CAS-induced
reset, we call spapr_dt_cas_updates() with only the set
of capabilities added since the previous call, since the other
capabilities will have already been addressed by the boot-time
device-tree this time around. In the unlikely event that
capabilities are *removed* since the previous CAS, we will
generate a CAS-induced reset. In the unlikely event that we
cannot fit the device-tree updates into the buffer provided
by the guest, well generate a CAS-induced reset.
2) When a CAS update results in the need to reset the machine and
include the updates in the boot-time device tree, we call the
spapr_dt_cas_updates() using the full set of negotiated
capabilities as part of the reset path. At initial boot, or after
a reset generated by something other than the CAS call itself,
this set will be empty, resulting in what should be the same
boot-time device-tree as we generated prior to this patch. For
CAS-induced reset, this routine will be called with the full set of
capabilities negotiated by the platform/guest in the previous
CAS call, which should result in CAS updates from previous call
being accounted for in the initial boot-time device tree.
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
[dwg: Changed an int -> bool conversion to be more explicit]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
6787d27b04