[PATCH v2] arm64: Restrict undef hook for cpufeature registers

[Will Deacon]

On Tue, Jun 08, 2021 at 04:20:43PM +0100, Catalin Marinas wrote:
> On Mon, May 17, 2021 at 01:02:56PM -0500, Rob Herring wrote:
> > From: Raphael Gault <raphael.gault at arm.com>
> > 
> > This commit modifies the mask of the mrs_hook declared in
> > arch/arm64/kernel/cpufeatures.c which emulates only feature register
> > access. This is necessary because this hook's mask was too large and
> > thus masking any mrs instruction, even if not related to the emulated
> > registers which made the pmu emulation inefficient.
> > 
> > Signed-off-by: Raphael Gault <raphael.gault at arm.com>
> > Signed-off-by: Rob Herring <robh at kernel.org>
> > ---
> > I don't *think* I'm going to need this for the perf userspace counter 
> > access, but this patch stands on its own as the PMU registers are not 
> > emulated. So please apply it.
> > 
> > v2:
> >  - Fix warning for set but unused sys_reg
> > ---
> >  arch/arm64/kernel/cpufeature.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> > index efed2830d141..c773f7c3c007 100644
> > --- a/arch/arm64/kernel/cpufeature.c
> > +++ b/arch/arm64/kernel/cpufeature.c
> > @@ -2905,8 +2905,8 @@ static int emulate_mrs(struct pt_regs *regs, u32 insn)
> >  }
> >  
> >  static struct undef_hook mrs_hook = {
> > -	.instr_mask = 0xfff00000,
> > -	.instr_val  = 0xd5300000,
> > +	.instr_mask = 0xffff0000,
> > +	.instr_val  = 0xd5380000,
> 
> Acked-by: Catalin Marinas <catalin.marinas at arm.com>
> 
> and changing Will's email address.

Should we update is_emulated() at the same time, or at least try to generate
the instr_val value here using the same constants?

Will