Power11 has the same PCR (Processor Compatibility Register) value, as Power10.
Due to this, QEMU considers Power11 as a valid compat-mode for Power10, ie. earlier it was possible to run QEMU with '-M pseries,max-compat-mode=power11 --cpu power10' Same PCR also introduced a regression where `-M pseries --cpu power10` boots as Power11 (ie. logical PVR is of Power11, even though PVR is Power10). The regression was due to 'do_client_architecture_support' checking for valid compat modes and finding Power11 to be a valid compat mode for Power10 (it happens even without passing 'max-compat-mode' explicitly). Fix compat-mode issue and regression, by ensuring a future Power processor (with a higher logical_pvr value, eg. P11) cannot be valid compat-mode for an older Power processor (eg. P10) Cc: Cédric Le Goater <c...@kaod.org> Cc: Daniel Henrique Barboza <danielhb...@gmail.com> Cc: Mahesh J Salgaonkar <mah...@linux.ibm.com> Cc: Madhavan Srinivasan <ma...@linux.ibm.com> Cc: Nicholas Piggin <npig...@gmail.com> Signed-off-by: Aditya Gupta <adit...@linux.ibm.com> --- Multiple alternative approaches were tried to fix this: 1. New PCR for Power11: No 2. 'Hacky fix': chose (n-1) entry in compat table in case of Power10. Commit: https://github.com/adi-g15-ibm/qemu/commit/c79bd667791883d4fb5e643979ae9c86a97bdf66 Pros: Doesn't require adding a new field Cons: Hacky fix, will need change if Power12 comes with same PCR as Power10 (unlikely) 3. Setting current Processor's .logical_pvr as the max_compat to be checked during CAS (Client Architecture Support). Commit: https://github.com/adi-g15-ibm/qemu/commit/30e430be71c6f3296017177298e54532570c2c87 This causes CAS to not consider Power11 if cpu is Power10 --- --- target/ppc/compat.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/target/ppc/compat.c b/target/ppc/compat.c index 12dd8ae290ca..168a3c06316f 100644 --- a/target/ppc/compat.c +++ b/target/ppc/compat.c @@ -139,6 +139,10 @@ static bool pcc_compat(PowerPCCPUClass *pcc, uint32_t compat_pvr, /* Outside specified range */ return false; } + if (compat->pvr > pcc->logical_pvr) { + /* Older CPU cannot support a newer processor's compat mode */ + return false; + } if (!(pcc->pcr_supported & compat->pcr_level)) { /* Not supported by this CPU */ return false; -- 2.45.1
