Re: [PATCH v4 21/23] arm64: hw_breakpoint: Allow EL2 breakpoints if running in HYP

[Will Deacon]

On Mon, Feb 15, 2016 at 05:46:56PM +0000, Will Deacon wrote:
> On Thu, Feb 11, 2016 at 06:40:02PM +0000, Marc Zyngier wrote:
> > With VHE, we place kernel {watch,break}-points at EL2 to get things
> > like kgdb and "perf -e mem:..." working.
> > 
> > This requires a bit of repainting in the low-level encore/decode,
> > but is otherwise pretty simple.
> > 
> > Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> > ---
> >  arch/arm64/include/asm/hw_breakpoint.h | 49 +++++++++++++++++++++-------------
> >  1 file changed, 31 insertions(+), 18 deletions(-)
> > 
> > diff --git a/arch/arm64/include/asm/hw_breakpoint.h b/arch/arm64/include/asm/hw_breakpoint.h
> > index 9732908..4d8d5a8 100644
> > --- a/arch/arm64/include/asm/hw_breakpoint.h
> > +++ b/arch/arm64/include/asm/hw_breakpoint.h
> > @@ -18,6 +18,7 @@
> >  
> >  #include <asm/cputype.h>
> >  #include <asm/cpufeature.h>
> > +#include <asm/virt.h>
> >  
> >  #ifdef __KERNEL__
> >  
> > @@ -35,24 +36,6 @@ struct arch_hw_breakpoint {
> >  	struct arch_hw_breakpoint_ctrl ctrl;
> >  };
> >  
> > -static inline u32 encode_ctrl_reg(struct arch_hw_breakpoint_ctrl ctrl)
> > -{
> > -	return (ctrl.len << 5) | (ctrl.type << 3) | (ctrl.privilege << 1) |
> > -		ctrl.enabled;
> > -}
> > -
> > -static inline void decode_ctrl_reg(u32 reg,
> > -				   struct arch_hw_breakpoint_ctrl *ctrl)
> > -{
> > -	ctrl->enabled	= reg & 0x1;
> > -	reg >>= 1;
> > -	ctrl->privilege	= reg & 0x3;
> > -	reg >>= 2;
> > -	ctrl->type	= reg & 0x3;
> > -	reg >>= 2;
> > -	ctrl->len	= reg & 0xff;
> > -}
> > -
> >  /* Breakpoint */
> >  #define ARM_BREAKPOINT_EXECUTE	0
> >  
> > @@ -62,6 +45,7 @@ static inline void decode_ctrl_reg(u32 reg,
> >  #define AARCH64_ESR_ACCESS_MASK	(1 << 6)
> >  
> >  /* Privilege Levels */
> > +#define AARCH64_BREAKPOINT_EL2	0
> >  #define AARCH64_BREAKPOINT_EL1	1
> >  #define AARCH64_BREAKPOINT_EL0	2
> >  
> > @@ -76,6 +60,35 @@ static inline void decode_ctrl_reg(u32 reg,
> >  #define ARM_KERNEL_STEP_ACTIVE	1
> >  #define ARM_KERNEL_STEP_SUSPEND	2
> >  
> > +#define DBG_HMC_HYP		(1 << 13)
> > +#define DBG_SSC_HYP		(3 << 14)
> 
> Why do we need to touch the SSC field at all?
> 
> > +
> > +static inline u32 encode_ctrl_reg(struct arch_hw_breakpoint_ctrl ctrl)
> > +{
> > +	u32 val = (ctrl.len << 5) | (ctrl.type << 3) | ctrl.enabled;
> > +
> > +	if (is_kernel_in_hyp_mode() && ctrl.privilege == AARCH64_BREAKPOINT_EL1)
> > +		val |= DBG_HMC_HYP | DBG_SSC_HYP | (AARCH64_BREAKPOINT_EL2 << 1);
> 
> I don't think this is correct. We want to allow, for example, a userspace
> watchpoint to fire thanks to something like put_user, so the encoding
> really needs to build up the PMC field (like we do already), then orr in
> the HMC field.

Hmm, I got my arm and my arm64 mixed up here. For the latter, we don't
actually support EL0+EL1 watchpoints, but I still think that the
{HMC,SSC,PMC} encoding of {1,00,xx} is cleaner.

Will