For now the optimization is supported only when no SMP is compiled in because it doesn't handle cross-modifying code.
The current stack page will cache also current pageWriteStamp for that page and could skip pageWriteStamp access if possible.
Any code fetch access missing trace cache will invalidate current stack page.
Code fetch accesses from another SMP threads should do the same to support SMP.
Next step:
- support SMP
- support pageWriteStamp access skipping for all other memory writes from all segments
implemented important CPU statistics which were used for Bochs CPU model performance analysis.
old statistics code from paging.cc and cpu.cc is replaced with new infrastructure.
In order to enale statitics collection in Bochs CPU:
- Enable statistics @ compilation time in cpu/cpustats.h
- Dump statistics periodically by adding -dumpstats N into Bochs command line
https://software.intel.com/sites/default/files/managed/c6/a9/319433-020.pdf
Most of the instructions are implemented, more on the way.
+ few bugfixes for legacy AVX-512 emulation
AVX-512: Fixed bug in VCMPPS masked instruction implementation with 512-bit data size
AVX-512: Fixed AVX-512 masked convert instructions with non-k0 mask (behaved as non masked versions)
AVX-512: Fixed missed #UD due to invalid EVEX prefix fields for several AVX-512 opcodes (VFIXUPIMMSS/SD, FMA)
I observed ~5% emulation slowdown ... thinking about possible mitigations
this fixes TLB issue with SMAP and SMEP features.
these features introduce a new behavior when page can be inaccessible by System (CPL=0).
Current behavior is accessBits was not supporting it but legacy (from Bochs 2.3.6) was.
The wrong behavior can be observed if user access a user page and system access the same page later.
user access is fine and pass SMEP/SMA checks and stores the translation in TLB.
the system access will hit the TLB and nobody could detect that system cannot access that page.
