On Fri, May 12, 2017 at 06:07:22PM +0100, Will Deacon wrote: > On Fri, May 12, 2017 at 11:15:20AM +0100, Mark Rutland wrote: > > Currently, cpus_set_cap() calls static_branch_enable_cpuslocked(), which > > must take the jump_label mutex. > > > > We call cpus_set_cap() in the secondary bringup path, from the idle > > thread where interrupts are disabled. Taking a mutex in this path "is a > > NONO" regardless of whether it's contended, and something we must avoid. > > Additionally, the secondary CPU doesn't hold the percpu rwsem (as this > > is held by the primary CPU), so this triggers a lockdep splat. > > > > This patch fixes both issues. The poking of static keys is deferred > > until enable_cpu_capabilities(), which runs in a suitable context on the > > boot CPU. To account for the static keys being set later, > > cpus_have_const_cap() is updated to use another static key to check > > whether the const cap keys have been initialised, falling back to the > > caps bitmap until this is the case. > > > > This means that users of cpus_have_const_cap() gain should only gain a > > single additional NOP in the fast path once the const caps are > > initialised, but should always see the current cap value. > > > > The hyp code should never dereference the caps array, since the caps are > > initialized before we run the module initcall to initialise hyp. A check > > is added to the hyp init code to docuemnt this requirement. > > > > This rework means that we can remove the *_cpuslocked() helpers added in > > commit d54bb72551b999dd ("arm64/cpufeature: Use > > static_branch_enable_cpuslocked()"). > > > > Signed-off-by: Mark Rutland <mark.rutl...@arm.com> > > Cc: Catalin Marinas <catalin.mari...@arm.com> > > Cc: Christoffer Dall <christoffer.d...@linaro.org> > > Cc: Marc Zyniger <marc.zyng...@arm.com> > > Cc: Peter Zijlstra <pet...@infradead.org> > > Cc: Sebastian Sewior <bige...@linutronix.de> > > Cc: Suzuki Poulose <suzuki.poul...@arm.com> > > Cc: Thomas Gleixner <t...@linutronix.de> > > Cc: Will Deacon <will.dea...@arm.com> > > --- > > arch/arm64/include/asm/cpufeature.h | 13 ++++++++++--- > > arch/arm64/include/asm/kvm_host.h | 8 ++++++-- > > arch/arm64/kernel/cpu_errata.c | 9 +-------- > > arch/arm64/kernel/cpufeature.c | 25 ++++++++++++++++++++++--- > > 4 files changed, 39 insertions(+), 16 deletions(-) > > > > Catalin, Will, assuming you're happy with the patch, it will need to go via > > the > > tip tree. > > Fine by me, although there's a typo in the comment (see below).
I'll take that as an Ack. :) > > /* > > - * Call initialization code, and switch to the full blown > > - * HYP code. > > + * Call initialization code, and switch to the full blown HYP code. > > + * If the cpucaps haven't been finialized yet, something has gone very > > + * wrong, and hyp will crash and burn when it uses any > > + * cpus_have_const_cap() wrapper. > > Typo: finialized Thanks; I've fixed that up locally now. ... v4 coming momentarily. Thanks, Mark.