[v4,13/15] KVM: arm: keep track of guest use of the debug registers
diff mbox

Message ID 1439213167-8988-14-git-send-email-zhichao.huang@linaro.org
State New
Headers show

Commit Message

Zhichao Huang Aug. 10, 2015, 1:26 p.m. UTC
We trap debug register accesses from guest all the time, and read the
BCR/WCR to indicate whether the guest has enabled any break/watch points
or not.

Signed-off-by: Zhichao Huang <zhichao.huang@linaro.org>
---
 arch/arm/include/asm/kvm_asm.h |  2 ++
 arch/arm/kvm/coproc.c          | 75 +++++++++++++++++++++++++++++++++++++++---
 2 files changed, 72 insertions(+), 5 deletions(-)

Comments

Christoffer Dall Sept. 2, 2015, 4:01 p.m. UTC | #1
On Mon, Aug 10, 2015 at 09:26:05PM +0800, Zhichao Huang wrote:
> We trap debug register accesses from guest all the time, and read the
> BCR/WCR to indicate whether the guest has enabled any break/watch points
> or not.
> 
> Signed-off-by: Zhichao Huang <zhichao.huang@linaro.org>
> ---
>  arch/arm/include/asm/kvm_asm.h |  2 ++
>  arch/arm/kvm/coproc.c          | 75 +++++++++++++++++++++++++++++++++++++++---
>  2 files changed, 72 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm/include/asm/kvm_asm.h b/arch/arm/include/asm/kvm_asm.h
> index 5b1c3eb..e9e1f0a 100644
> --- a/arch/arm/include/asm/kvm_asm.h
> +++ b/arch/arm/include/asm/kvm_asm.h
> @@ -65,7 +65,9 @@
>  #define NR_CP14_REGS	66	/* Number of regs (incl. invalid) */
>  
>  #define KVM_ARM_DEBUG_HOST_INUSE_SHIFT	0
> +#define KVM_ARM_DEBUG_GUEST_INUSE_SHIFT	1
>  #define KVM_ARM_DEBUG_HOST_INUSE	(1 << KVM_ARM_DEBUG_HOST_INUSE_SHIFT)
> +#define KVM_ARM_DEBUG_GUEST_INUSE	(1 << KVM_ARM_DEBUG_GUEST_INUSE_SHIFT)
>  
>  #define ARM_EXCEPTION_RESET	  0
>  #define ARM_EXCEPTION_UNDEFINED   1
> diff --git a/arch/arm/kvm/coproc.c b/arch/arm/kvm/coproc.c
> index b37afd6..d9dcd28b 100644
> --- a/arch/arm/kvm/coproc.c
> +++ b/arch/arm/kvm/coproc.c
> @@ -220,7 +220,22 @@ bool access_vm_reg(struct kvm_vcpu *vcpu,
>  	return true;
>  }
>  
> -static bool trap_debug32(struct kvm_vcpu *vcpu,
> +/* Indicate whether the guest has enabled any break/watch points or not. */
> +static bool guest_debug_in_use(struct kvm_vcpu *vcpu)
> +{
> +	unsigned int i;
> +
> +	for (i = 0; i < ARM_MAX_BRP; i++)
> +		if (vcpu->arch.cp14[cp14_DBGBCR0 + i] & 0x1)
> +			return true;
> +	for (i = 0; i < ARM_MAX_WRP; i++)
> +		if (vcpu->arch.cp14[cp14_DBGWCR0 + i] & 0x1)
> +			return true;
> +
> +	return false;
> +}
> +
> +static bool __trap_debug32(struct kvm_vcpu *vcpu,
>  			const struct coproc_params *p,
>  			const struct coproc_reg *r)
>  {
> @@ -232,6 +247,56 @@ static bool trap_debug32(struct kvm_vcpu *vcpu,
>  	return true;
>  }
>  
> +/*
> + * We want to avoid world-switching all the DBG registers all the
> + * time:
> + *
> + * When we are about to run a guest, we have the following cases:
> + *
> + * 1) Neither the host nor the guest has configured any [WB]points
> + * 2) Only the host has configured any [WB]points
> + * 3) Only the guest has configured any [WB]points
> + * 4) Both the host and the guest have configured any [WB]points
> + *
> + * - In case (1), KVM should enable trapping and swtich the register
						    switch
> + *   state on guest accesses.
> + * - In cases (2), (3), and (4) we must switch the register state on each
> + *   entry/exit.
> + *
> + * For ARMv7, if the CONFIG_HAVE_HW_BREAKPOINT is set, ARM_DSCR_MDBGEN
> + * is always set(ARM64 use it to indicate that debug registers are actively
        add space  ^
> + * in use).

While I like having the overall explanation of the flow somewhere, I
feel this is a strange place to put it.  Perhaps there is a more
suitable location?

> + *
> + * - We add a function reading the break/watch control variables directly to
> + *   indicate whether the host has enabled any break/watch points or not.
> + *   We only call the function upon guest entry, after preempt_disable() and
> + *   local_irq_disable(), so there is no race for it.

This paragraph of the commenting doesn't seem to fit with the rest, and
didn't we cover this already in a previous patch?

> + *
> + * - We trap debug register accesses from guest all the time, and read the
> + *   BCR/WCR to indicate whether the guest has enabled any break/watch points
> + *   or not.

do we trap all the time?  not if we're switching the state I suppose?

> + *
> + * For this, we can keep track of the host/guest use of debug registers,
> + * and skip the save/restore dance when neither the host nor the guest has
> + * configured any [WB]points.
> + */
> +static bool trap_debug32(struct kvm_vcpu *vcpu,
> +			const struct coproc_params *p,
> +			const struct coproc_reg *r)
> +{
> +	__trap_debug32(vcpu, p, r);
> +
> +	if (p->is_write) {
> +		if ((vcpu->arch.cp14[r->reg] & 0x1) ||
> +		    guest_debug_in_use(vcpu))
> +			vcpu->arch.debug_flags |= KVM_ARM_DEBUG_GUEST_INUSE;
> +		else
> +			vcpu->arch.debug_flags &= ~KVM_ARM_DEBUG_GUEST_INUSE;

I don't understand this logic, if we are enabling one of the w/b points
or if there was already an enabled w/b point, then we set the flag, but
if you disable a single one then you clear the flag?

It looks to me like you're mixing two approaches here;  either read
through all the registers whenever you need to know to set the flag or
not, or you keep track of this on every read/write of the registers.

> +	}
> +
> +	return true;
> +}
> +
>  /* DBGIDR (RO) Debug ID */
>  static bool trap_dbgidr(struct kvm_vcpu *vcpu,
>  			const struct coproc_params *p,
> @@ -419,13 +484,13 @@ static const struct coproc_reg cp15_regs[] = {
>  #define DBG_BCR_BVR_WCR_WVR(n)					\
>  	/* DBGBVRn */						\
>  	{ CRn( 0), CRm((n)), Op1( 0), Op2( 4), is32,		\
> -	  trap_debug32,	reset_val, (cp14_DBGBVR0 + (n)), 0 },	\
> +	  __trap_debug32, reset_val, (cp14_DBGBVR0 + (n)), 0 },	\
>  	/* DBGBCRn */						\
>  	{ CRn( 0), CRm((n)), Op1( 0), Op2( 5), is32,		\
>  	  trap_debug32,	reset_val, (cp14_DBGBCR0 + (n)), 0 },	\
>  	/* DBGWVRn */						\
>  	{ CRn( 0), CRm((n)), Op1( 0), Op2( 6), is32,		\
> -	  trap_debug32,	reset_val, (cp14_DBGWVR0 + (n)), 0 },	\
> +	  __trap_debug32, reset_val, (cp14_DBGWVR0 + (n)), 0 },	\
>  	/* DBGWCRn */						\
>  	{ CRn( 0), CRm((n)), Op1( 0), Op2( 7), is32,		\
>  	  trap_debug32,	reset_val, (cp14_DBGWCR0 + (n)), 0 }
> @@ -462,7 +527,7 @@ static const struct coproc_reg cp14_regs[] = {
>  	/* DBGDSAR (64bit) */
>  	{ CRn( 0), CRm( 2), Op1( 0), Op2( 0), is64, trap_raz_wi },
>  	/* DBGDSCRext */
> -	{ CRn( 0), CRm( 2), Op1( 0), Op2( 2), is32, trap_debug32,
> +	{ CRn( 0), CRm( 2), Op1( 0), Op2( 2), is32, __trap_debug32,
>  				reset_val, cp14_DBGDSCRext, 0 },
>  	DBG_BCR_BVR_WCR_WVR(2),
>  	/* DBGDTRTXext */
> @@ -474,7 +539,7 @@ static const struct coproc_reg cp14_regs[] = {
>  	DBG_BCR_BVR_WCR_WVR(5),
>  	DBG_BCR_BVR_WCR_WVR(6),
>  	/* DBGVCR */
> -	{ CRn( 0), CRm( 7), Op1( 0), Op2( 0), is32, trap_debug32 },
> +	{ CRn( 0), CRm( 7), Op1( 0), Op2( 0), is32, __trap_debug32 },
>  	DBG_BCR_BVR_WCR_WVR(7),
>  	DBG_BCR_BVR_WCR_WVR(8),
>  	DBG_BCR_BVR_WCR_WVR(9),
> -- 
> 1.7.12.4
> 

So __trap_debug32 is for the non-control registers and trap-debug32 is
for the control registers?

I think specifically naming the control register function
trap_debug_cr would be cleaner in that case.

Thanks,
-Christoffer

--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Zhichao Huang Sept. 29, 2015, 5:36 a.m. UTC | #2
On 2015/9/3 0:01, Christoffer Dall wrote:
> On Mon, Aug 10, 2015 at 09:26:05PM +0800, Zhichao Huang wrote:
>>  
>> -static bool trap_debug32(struct kvm_vcpu *vcpu,
>> +/* Indicate whether the guest has enabled any break/watch points or not. */
>> +static bool guest_debug_in_use(struct kvm_vcpu *vcpu)
>> +{
>> +	unsigned int i;
>> +
>> +	for (i = 0; i < ARM_MAX_BRP; i++)
>> +		if (vcpu->arch.cp14[cp14_DBGBCR0 + i] & 0x1)
>> +			return true;
>> +	for (i = 0; i < ARM_MAX_WRP; i++)
>> +		if (vcpu->arch.cp14[cp14_DBGWCR0 + i] & 0x1)
>> +			return true;
>> +
>> +	return false;
>> +}
>> +
>> +static bool __trap_debug32(struct kvm_vcpu *vcpu,
>>  			const struct coproc_params *p,
>>  			const struct coproc_reg *r)
>>  {
>> @@ -232,6 +247,56 @@ static bool trap_debug32(struct kvm_vcpu *vcpu,
>>  	return true;
>>  }
>>  

>> +static bool trap_debug32(struct kvm_vcpu *vcpu,
>> +			const struct coproc_params *p,
>> +			const struct coproc_reg *r)
>> +{
>> +	__trap_debug32(vcpu, p, r);
>> +
>> +	if (p->is_write) {
>> +		if ((vcpu->arch.cp14[r->reg] & 0x1) ||
>> +		    guest_debug_in_use(vcpu))
>> +			vcpu->arch.debug_flags |= KVM_ARM_DEBUG_GUEST_INUSE;
>> +		else
>> +			vcpu->arch.debug_flags &= ~KVM_ARM_DEBUG_GUEST_INUSE;
> 
> I don't understand this logic, if we are enabling one of the w/b points
> or if there was already an enabled w/b point, then we set the flag, but
> if you disable a single one then you clear the flag?
> 
> It looks to me like you're mixing two approaches here;  either read
> through all the registers whenever you need to know to set the flag or
> not, or you keep track of this on every read/write of the registers.
> 

I did it in the function guest_debug_in_use(), which will read through all the
registers.


> 
> So __trap_debug32 is for the non-control registers and trap-debug32 is
> for the control registers?
> 
> I think specifically naming the control register function
> trap_debug_cr would be cleaner in that case.
> 

OK.

> Thanks,
> -Christoffer
> 
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Patch
diff mbox

diff --git a/arch/arm/include/asm/kvm_asm.h b/arch/arm/include/asm/kvm_asm.h
index 5b1c3eb..e9e1f0a 100644
--- a/arch/arm/include/asm/kvm_asm.h
+++ b/arch/arm/include/asm/kvm_asm.h
@@ -65,7 +65,9 @@ 
 #define NR_CP14_REGS	66	/* Number of regs (incl. invalid) */
 
 #define KVM_ARM_DEBUG_HOST_INUSE_SHIFT	0
+#define KVM_ARM_DEBUG_GUEST_INUSE_SHIFT	1
 #define KVM_ARM_DEBUG_HOST_INUSE	(1 << KVM_ARM_DEBUG_HOST_INUSE_SHIFT)
+#define KVM_ARM_DEBUG_GUEST_INUSE	(1 << KVM_ARM_DEBUG_GUEST_INUSE_SHIFT)
 
 #define ARM_EXCEPTION_RESET	  0
 #define ARM_EXCEPTION_UNDEFINED   1
diff --git a/arch/arm/kvm/coproc.c b/arch/arm/kvm/coproc.c
index b37afd6..d9dcd28b 100644
--- a/arch/arm/kvm/coproc.c
+++ b/arch/arm/kvm/coproc.c
@@ -220,7 +220,22 @@  bool access_vm_reg(struct kvm_vcpu *vcpu,
 	return true;
 }
 
-static bool trap_debug32(struct kvm_vcpu *vcpu,
+/* Indicate whether the guest has enabled any break/watch points or not. */
+static bool guest_debug_in_use(struct kvm_vcpu *vcpu)
+{
+	unsigned int i;
+
+	for (i = 0; i < ARM_MAX_BRP; i++)
+		if (vcpu->arch.cp14[cp14_DBGBCR0 + i] & 0x1)
+			return true;
+	for (i = 0; i < ARM_MAX_WRP; i++)
+		if (vcpu->arch.cp14[cp14_DBGWCR0 + i] & 0x1)
+			return true;
+
+	return false;
+}
+
+static bool __trap_debug32(struct kvm_vcpu *vcpu,
 			const struct coproc_params *p,
 			const struct coproc_reg *r)
 {
@@ -232,6 +247,56 @@  static bool trap_debug32(struct kvm_vcpu *vcpu,
 	return true;
 }
 
+/*
+ * We want to avoid world-switching all the DBG registers all the
+ * time:
+ *
+ * When we are about to run a guest, we have the following cases:
+ *
+ * 1) Neither the host nor the guest has configured any [WB]points
+ * 2) Only the host has configured any [WB]points
+ * 3) Only the guest has configured any [WB]points
+ * 4) Both the host and the guest have configured any [WB]points
+ *
+ * - In case (1), KVM should enable trapping and swtich the register
+ *   state on guest accesses.
+ * - In cases (2), (3), and (4) we must switch the register state on each
+ *   entry/exit.
+ *
+ * For ARMv7, if the CONFIG_HAVE_HW_BREAKPOINT is set, ARM_DSCR_MDBGEN
+ * is always set(ARM64 use it to indicate that debug registers are actively
+ * in use).
+ *
+ * - We add a function reading the break/watch control variables directly to
+ *   indicate whether the host has enabled any break/watch points or not.
+ *   We only call the function upon guest entry, after preempt_disable() and
+ *   local_irq_disable(), so there is no race for it.
+ *
+ * - We trap debug register accesses from guest all the time, and read the
+ *   BCR/WCR to indicate whether the guest has enabled any break/watch points
+ *   or not.
+ *
+ * For this, we can keep track of the host/guest use of debug registers,
+ * and skip the save/restore dance when neither the host nor the guest has
+ * configured any [WB]points.
+ */
+static bool trap_debug32(struct kvm_vcpu *vcpu,
+			const struct coproc_params *p,
+			const struct coproc_reg *r)
+{
+	__trap_debug32(vcpu, p, r);
+
+	if (p->is_write) {
+		if ((vcpu->arch.cp14[r->reg] & 0x1) ||
+		    guest_debug_in_use(vcpu))
+			vcpu->arch.debug_flags |= KVM_ARM_DEBUG_GUEST_INUSE;
+		else
+			vcpu->arch.debug_flags &= ~KVM_ARM_DEBUG_GUEST_INUSE;
+	}
+
+	return true;
+}
+
 /* DBGIDR (RO) Debug ID */
 static bool trap_dbgidr(struct kvm_vcpu *vcpu,
 			const struct coproc_params *p,
@@ -419,13 +484,13 @@  static const struct coproc_reg cp15_regs[] = {
 #define DBG_BCR_BVR_WCR_WVR(n)					\
 	/* DBGBVRn */						\
 	{ CRn( 0), CRm((n)), Op1( 0), Op2( 4), is32,		\
-	  trap_debug32,	reset_val, (cp14_DBGBVR0 + (n)), 0 },	\
+	  __trap_debug32, reset_val, (cp14_DBGBVR0 + (n)), 0 },	\
 	/* DBGBCRn */						\
 	{ CRn( 0), CRm((n)), Op1( 0), Op2( 5), is32,		\
 	  trap_debug32,	reset_val, (cp14_DBGBCR0 + (n)), 0 },	\
 	/* DBGWVRn */						\
 	{ CRn( 0), CRm((n)), Op1( 0), Op2( 6), is32,		\
-	  trap_debug32,	reset_val, (cp14_DBGWVR0 + (n)), 0 },	\
+	  __trap_debug32, reset_val, (cp14_DBGWVR0 + (n)), 0 },	\
 	/* DBGWCRn */						\
 	{ CRn( 0), CRm((n)), Op1( 0), Op2( 7), is32,		\
 	  trap_debug32,	reset_val, (cp14_DBGWCR0 + (n)), 0 }
@@ -462,7 +527,7 @@  static const struct coproc_reg cp14_regs[] = {
 	/* DBGDSAR (64bit) */
 	{ CRn( 0), CRm( 2), Op1( 0), Op2( 0), is64, trap_raz_wi },
 	/* DBGDSCRext */
-	{ CRn( 0), CRm( 2), Op1( 0), Op2( 2), is32, trap_debug32,
+	{ CRn( 0), CRm( 2), Op1( 0), Op2( 2), is32, __trap_debug32,
 				reset_val, cp14_DBGDSCRext, 0 },
 	DBG_BCR_BVR_WCR_WVR(2),
 	/* DBGDTRTXext */
@@ -474,7 +539,7 @@  static const struct coproc_reg cp14_regs[] = {
 	DBG_BCR_BVR_WCR_WVR(5),
 	DBG_BCR_BVR_WCR_WVR(6),
 	/* DBGVCR */
-	{ CRn( 0), CRm( 7), Op1( 0), Op2( 0), is32, trap_debug32 },
+	{ CRn( 0), CRm( 7), Op1( 0), Op2( 0), is32, __trap_debug32 },
 	DBG_BCR_BVR_WCR_WVR(7),
 	DBG_BCR_BVR_WCR_WVR(8),
 	DBG_BCR_BVR_WCR_WVR(9),