On Fri, Jan 05, 2018 at 06:12:19PM -0800, Tim Chen wrote: > From: Tim Chen <tim.c.c...@linux.intel.com> > From: Andrea Arcangeli <aarca...@redhat.com> > > There are 2 ways to control IBRS > > 1. At boot time > noibrs kernel boot parameter will disable IBRS usage > > Otherwise if the above parameters are not specified, the system > will enable ibrs and ibpb usage if the cpu supports it. > > 2. At run time > echo 0 > /sys/kernel/debug/x86/ibrs_enabled will turn off IBRS > echo 1 > /sys/kernel/debug/x86/ibrs_enabled will turn on IBRS in kernel > echo 2 > /sys/kernel/debug/x86/ibrs_enabled will turn on IBRS in both > userspace and kernel > > The implementation was updated with input and suggestions from Andrea > Arcangeli. > > Signed-off-by: Tim Chen <tim.c.c...@linux.intel.com> > --- > arch/x86/entry/calling.h | 42 ++++++++-- > arch/x86/include/asm/spec_ctrl.h | 15 ++++ > arch/x86/kernel/cpu/Makefile | 1 + > arch/x86/kernel/cpu/scattered.c | 2 + > arch/x86/kernel/cpu/spec_ctrl.c | 160 > +++++++++++++++++++++++++++++++++++++++ > 5 files changed, 214 insertions(+), 6 deletions(-) > create mode 100644 arch/x86/include/asm/spec_ctrl.h > create mode 100644 arch/x86/kernel/cpu/spec_ctrl.c > > diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h > index 09c870d..6b65d47 100644 > --- a/arch/x86/entry/calling.h > +++ b/arch/x86/entry/calling.h > @@ -373,35 +373,55 @@ For 32-bit we have the following conventions - kernel > is built with > .endm > > .macro ENABLE_IBRS > - ALTERNATIVE "jmp .Lskip_\@", "", X86_FEATURE_SPEC_CTRL > + testl $1, dynamic_ibrs > + jz .Lskip_\@ > + > PUSH_MSR_REGS > WRMSR_ASM $MSR_IA32_SPEC_CTRL, $SPEC_CTRL_FEATURE_ENABLE_IBRS > POP_MSR_REGS > + jmp .Ldone_\@ > + > .Lskip_\@: > + lfence > +.Ldone_\@: > .endm > > .macro DISABLE_IBRS > - ALTERNATIVE "jmp .Lskip_\@", "", X86_FEATURE_SPEC_CTRL > + testl $1, dynamic_ibrs
On every system call we end up hammering on this 'dynamic_ibrs' variable. And it looks like it can be flipped via the IPI mechanism. Would it make sense for this to be per-cpu?
