Similarly as we already do for arm64, for mitigation is necessary to
flush branch predictor when we:
- do task switch
- receive prefetch abort on non-userspace address
The user can disable this mitigation by setting 'machdep.disable_bp_hardening'
sysctl variable, or it can check actual system status by reading
'machdep.spectre_v2_safe'
The situation is complicated by fact that:
- for Cortex-A8, the BPIALL instruction is effectively NOP until the IBE bit
in ACTLR is set.
- for Cortex-A15, the BPIALL is always NOP. The branch predictor can be
only flushed by doing ICIALLU with special bit (Enable invalidates of BTB)
set in ACTLR.
Since access to the ACTLR register is locked to secure monitor/firmware on
most boards, they will also need update of firmware / U-boot.
In worst case, when secure monitor is on-chip ROM (e.g. PandaBoard),
the board is unfixable.
MFC after: 2 weeks
Reviewed by: imp, emaste
Differential Revision: https://reviews.freebsd.org/D13931
These quirks are intended for optimizing CPU performance, not for
applying errata workarounds. Nobody can expect that CPU with unfixed
errata is stable enough to execute the kernel until quirks are applied.
MFC after: 3 weeks
The bits in the aux control register vary based on the processor type. In
the past we've always just set the 'smp' and "broadcast tlb/cache ops' bits,
which worked fine for the first few SoCs we supported. Now that we support
most of the cortex-a series processors, it's important to get the right bits
set based on the processor type.
Submitted by: Svatopluk Kraus <onwahe@gmail.com>
mechanism defined for armv7 (and also present on some armv6 chips including
the arm1176 used on rpi). The information is parsed into a global cpuinfo
structure, which will be used by (upcoming) new cache and tlb maintenance
code to handle cpu-specific variations of the maintence sequences.
Submitted by: Svatopluk Kraus <onwahe@gmail.com>,
Michal Meloun <meloun@miracle.cz
