Re: [PATCH v3 21/23] arm64: hw_breakpoint: Allow EL2 breakpoints if running in HYP

Marc Zyngier
2016-02-08T16:45:44Z

On 08/02/16 15:56, Catalin Marinas wrote:
> On Wed, Feb 03, 2016 at 06:00:14PM +0000, Marc Zyngier wrote:
>> @@ -76,6 +59,36 @@ 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)
>> +
>> +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;
>> + else
>> + val |= ctrl.privilege << 1;
>> +
>> + return val;
>> +}
>> +
>> +static inline void decode_ctrl_reg(u32 reg,
>> + struct arch_hw_breakpoint_ctrl *ctrl)
>> +{
>> + ctrl->enabled = reg & 0x1;
>> + reg >>= 1;
>> + if (is_kernel_in_hyp_mode())
>> + ctrl->privilege = !!(reg & (DBG_HMC_HYP >> 1));
>
> I don't particularly like this part as it's not clear just by looking at
> the code that it, in fact, generates AARCH64_BREAKPOINT_EL1. I would
> make this clearer:
>
> if (is_kernel_in_hyp_mode() && (reg & (DBG_HMC_HYP >> 1)))
> ctrl->privilege = AARCH64_BREAKPOINT_EL1;
>
> Alternatively, you could define the PMC field value as:
>
> #define AARCH64_BREAKPOINT_EL2 0
>
> and change the privilege to EL1 after masking, something like:
>
> ctrl->privilege = reg & 0x3;
> if (ctrl->privilege == AARCH64_BREAKPOINT_EL2)
> ctrl->privilege = AARCH64_BREAKPOINT_EL1;
>
> BTW, do we need to check is_kernel_in_hyp_mode() when decoding? Is there
> anything else that could have set this SSC/HMC/PMC fields other than
> encode_ctrl_reg()?

I was being overzealous, and your solution is clearly better. I ended up with the following:

diff --git a/arch/arm64/include/asm/hw_breakpoint.h b/arch/arm64/include/asm/hw_breakpoint.h
index 9732908..c872b2f 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)
+
+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;
+ else
+ val |= ctrl.privilege << 1;
+
+ return val;
+}
+
+static inline void decode_ctrl_reg(u32 reg,
+ struct arch_hw_breakpoint_ctrl *ctrl)
+{
+ ctrl->enabled = reg & 0x1;
+ reg >>= 1;
+ ctrl->privilege = reg & 0x3;
+ if (ctrl->privilege == AARCH64_BREAKPOINT_EL2)
+ ctrl->privilege = AARCH64_BREAKPOINT_EL1;
+ reg >>= 2;
+ ctrl->type = reg & 0x3;
+ reg >>= 2;
+ ctrl->len = reg & 0xff;
+}
+
/*
* Limits.
* Changing these will require modifications to the register accessors.

Was that what you had in mind?

Thanks,

M.
--
Jazz is not dead. It just smells funny...