[PATCH v3 1/3] kvm: arm debug: introduce helper for single-step

[PATCH v3 1/3] kvm: arm debug: introduce helper for single-step

[Alex Bennée]

After emulating instructions we may want return to user-space to
handle a single-step. If single-step is enabled the helper set the run
structure for return and returns true.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Julien Thierry <julien.thierry@arm.com>
---
v2
  - kvm_arm_maybe_return_debug -> kvm_arm_handle_step_debug
  - return bool, true if return to userspace is required
---
 arch/arm/include/asm/kvm_host.h   |  5 +++++
 arch/arm64/include/asm/kvm_host.h |  1 +
 arch/arm64/kvm/debug.c            | 22 ++++++++++++++++++++++
 3 files changed, 28 insertions(+)

diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index 4a879f6ff13b..26a1ea6c6542 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -285,6 +285,11 @@ static inline void kvm_arm_init_debug(void) {}
 static inline void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) {}
 static inline void kvm_arm_clear_debug(struct kvm_vcpu *vcpu) {}
 static inline void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu) {}
+static inline bool kvm_arm_handle_step_debug(struct kvm_vcpu *vcpu,
+					     struct kvm_run *run)
+{
+	return false;
+}
 
 int kvm_arm_vcpu_arch_set_attr(struct kvm_vcpu *vcpu,
 			       struct kvm_device_attr *attr);
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index e923b58606e2..bbfd6a2adb2b 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -369,6 +369,7 @@ void kvm_arm_init_debug(void);
 void kvm_arm_setup_debug(struct kvm_vcpu *vcpu);
 void kvm_arm_clear_debug(struct kvm_vcpu *vcpu);
 void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu);
+bool kvm_arm_handle_step_debug(struct kvm_vcpu *vcpu, struct kvm_run *run);
 int kvm_arm_vcpu_arch_set_attr(struct kvm_vcpu *vcpu,
 			       struct kvm_device_attr *attr);
 int kvm_arm_vcpu_arch_get_attr(struct kvm_vcpu *vcpu,
diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
index dbadfaf850a7..95afd22a4634 100644
--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c
@@ -221,3 +221,25 @@ void kvm_arm_clear_debug(struct kvm_vcpu *vcpu)
 		}
 	}
 }
+
+
+/*
+ * When KVM has successfully emulated the instruction we might want to
+ * return to user space with a KVM_EXIT_DEBUG. We can only do this
+ * once the emulation is complete though so for userspace emulations
+ * we have to wait until we have re-entered KVM before calling this
+ * helper.
+ *
+ * Return true (and set exit_reason) to return to userspace or false
+ * if no further action required.
+ */
+
+bool kvm_arm_handle_step_debug(struct kvm_vcpu *vcpu, struct kvm_run *run)
+{
+	if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
+		run->exit_reason = KVM_EXIT_DEBUG;
+		run->debug.arch.hsr = ESR_ELx_EC_SOFTSTP_LOW << ESR_ELx_EC_SHIFT;
+		return true;
+	}
+	return false;
+}
-- 
2.15.0

[PATCH v3 2/3] kvm: arm64: handle single-stepping trapped instructions

[Alex Bennée]

If we are using guest debug to single-step the guest we need to ensure
we exit after emulating the instruction. This only affects
instructions completely emulated by the kernel. For userspace emulated
instructions we need to exit and return to complete the emulation.

The kvm_arm_handle_step_debug() helper sets up the necessary exit
state if needed.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Julien Thierry <julien.thierry@arm.com>
---
v2
  - use helper from patch 1
  - if (handled > 0) instead of if (handled) so errors propagate
---
 arch/arm64/kvm/handle_exit.c | 47 +++++++++++++++++++++++++++++++-------------
 1 file changed, 33 insertions(+), 14 deletions(-)

diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index 7debb74843a0..af1c804742f6 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -178,6 +178,38 @@ static exit_handle_fn kvm_get_exit_handler(struct kvm_vcpu *vcpu)
 	return arm_exit_handlers[hsr_ec];
 }
 
+/*
+ * We may be single-stepping an emulated instruction. If the emulation
+ * has been completed in-kernel we can return to userspace with a
+ * KVM_EXIT_DEBUG, otherwise the userspace needs to complete its
+ * emulation first.
+ */
+
+static int handle_trap_exceptions(struct kvm_vcpu *vcpu, struct kvm_run *run)
+{
+	int handled;
+
+	/*
+	 * See ARM ARM B1.14.1: "Hyp traps on instructions
+	 * that fail their condition code check"
+	 */
+	if (!kvm_condition_valid(vcpu)) {
+		kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu));
+		handled = 1;
+	} else {
+		exit_handle_fn exit_handler;
+
+		exit_handler = kvm_get_exit_handler(vcpu);
+		handled = exit_handler(vcpu, run);
+	}
+
+	/* helper sets exit_reason if we need to return to userspace */
+	if (handled > 0 && kvm_arm_handle_step_debug(vcpu, run))
+		handled = 0;
+
+	return handled;
+}
+
 /*
  * Return > 0 to return to guest, < 0 on error, 0 (and set exit_reason) on
  * proper exit to userspace.
@@ -185,8 +217,6 @@ static exit_handle_fn kvm_get_exit_handler(struct kvm_vcpu *vcpu)
 int handle_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
 		       int exception_index)
 {
-	exit_handle_fn exit_handler;
-
 	if (ARM_SERROR_PENDING(exception_index)) {
 		u8 hsr_ec = ESR_ELx_EC(kvm_vcpu_get_hsr(vcpu));
 
@@ -214,18 +244,7 @@ int handle_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
 		kvm_inject_vabt(vcpu);
 		return 1;
 	case ARM_EXCEPTION_TRAP:
-		/*
-		 * See ARM ARM B1.14.1: "Hyp traps on instructions
-		 * that fail their condition code check"
-		 */
-		if (!kvm_condition_valid(vcpu)) {
-			kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu));
-			return 1;
-		}
-
-		exit_handler = kvm_get_exit_handler(vcpu);
-
-		return exit_handler(vcpu, run);
+		return handle_trap_exceptions(vcpu, run);
 	case ARM_EXCEPTION_HYP_GONE:
 		/*
 		 * EL2 has been reset to the hyp-stub. This happens when a guest
-- 
2.15.0

[PATCH v3 3/3] kvm: arm64: handle single-step of userspace mmio instructions

[Alex Bennée]

The system state of KVM when using userspace emulation is not complete
until we return into KVM_RUN. To handle mmio related updates we wait
until they have been committed and then schedule our KVM_EXIT_DEBUG.

The kvm_arm_handle_step_debug() helper tells us if we need to return
and sets up the exit_reason for us.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

---
v2
  - call helper directly from kvm_arch_vcpu_ioctl_run
v3
  - return 0 (ioctl success) instead of 1
---
 virt/kvm/arm/arm.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index 95cba0799828..b40440defca1 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -625,6 +625,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
 		ret = kvm_handle_mmio_return(vcpu, vcpu->run);
 		if (ret)
 			return ret;
+		if (kvm_arm_handle_step_debug(vcpu, vcpu->run))
+			return 0;
+
 	}
 
 	if (run->immediate_exit)
-- 
2.15.0

Re: [PATCH v3 3/3] kvm: arm64: handle single-step of userspace mmio instructions

[Julien Thierry]

On 16/11/17 15:39, Alex Bennée wrote:
> The system state of KVM when using userspace emulation is not complete
> until we return into KVM_RUN. To handle mmio related updates we wait
> until they have been committed and then schedule our KVM_EXIT_DEBUG.
> 
> The kvm_arm_handle_step_debug() helper tells us if we need to return
> and sets up the exit_reason for us.
> 
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> 

Reviewed-by: Julien Thierry <julien.thierry@arm.com>

> ---
> v2
>    - call helper directly from kvm_arch_vcpu_ioctl_run
> v3
>    - return 0 (ioctl success) instead of 1
> ---
>   virt/kvm/arm/arm.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index 95cba0799828..b40440defca1 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -625,6 +625,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
>   		ret = kvm_handle_mmio_return(vcpu, vcpu->run);
>   		if (ret)
>   			return ret;
> +		if (kvm_arm_handle_step_debug(vcpu, vcpu->run))
> +			return 0;
> +
>   	}
>   
>   	if (run->immediate_exit)
> 

-- 
Julien Thierry