device: 0.792
instruction: 0.606
vnc: 0.601
graphic: 0.525
mistranslation: 0.519
socket: 0.510
other: 0.504
network: 0.458
semantic: 0.448
boot: 0.382
assembly: 0.160
KVM: 0.125

powerpc 7450 MMU initialization broken

The 7540 family of PPCs' MMU can update TLBs using hardware search (like a 604 or 7400) but also using a software algorithm. The mechanism used is defined by HID0[STEN].

By default (CPU reset) HID0 is set to 0x80000000 (BTW; another small bug, qemu doesn't set the hardwired MSB), hence
the software-table lookup feature is *disabled*. However, the default (and immutable) 'mmu_model' for this CPU family is POWERC_MMU_SOFT_74XX which choses the soft TLB replacement scheme.

To fix this:

1) the initial mmu_model for the 7450 family (includes 7441, 7445, 7451, 7455, 7457, 7447, 7448) should be: POWERPC_MMU_32B
2) when HID0[STEN] is written then the mmu_model should be changed accordingly (I'm not familiar enough with the qemu internal state to judge if any cached state would have to be updated).

Looking through old bug tickets... is this still an issue with the latest version of QEMU? Or could we close this ticket nowadays?


From looking at the source code of 5.1.0-rc3 (target/ppc/translate_init.inc.c) it seems that this is still an issue.


This is an automated cleanup. This bug report has been moved to QEMU's
new bug tracker on gitlab.com and thus gets marked as 'expired' now.
Please continue with the discussion here:

 https://gitlab.com/qemu-project/qemu/-/issues/86