[PATCH v2 1/5] KVM: Add arch specific interfaces for sampling guest callchains

[Tianyi Liu <i.pear@xxxxxxxxxxx>]

This patch adds three architecture specific interfaces and x86
implementations used by `perf kvm`:

- kvm_arch_vcpu_get_frame_pointer: Return the frame pointer of vcpu,
  for x86 it's RBP, and for arm64 it's x29.

- kvm_arch_vcpu_read_virt: Read data from a virtual address
  of the given guest vm.

- kvm_arch_vcpu_is_64bit: Return whether the vcpu is working in 64-bit
  mode. It's used for determining the size of a stack frame.

Since arm64 hasn't provided some foundational infrastructure,
stub the arm64 implementation for now because it's a bit complex.

Signed-off-by: Tianyi Liu <i.pear@xxxxxxxxxxx>
---
 arch/arm64/kvm/arm.c     | 17 +++++++++++++++++
 arch/x86/kvm/x86.c       | 18 ++++++++++++++++++
 include/linux/kvm_host.h |  4 ++++
 3 files changed, 39 insertions(+)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 4866b3f7b..b57b88c58 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -571,6 +571,23 @@ unsigned long kvm_arch_vcpu_get_ip(struct kvm_vcpu *vcpu)
 {
 	return *vcpu_pc(vcpu);
 }
+
+unsigned long kvm_arch_vcpu_get_frame_pointer(struct kvm_vcpu *vcpu)
+{
+	/* TODO: implement */
+	return NULL;
+}
+
+bool kvm_arch_vcpu_read_virt(struct kvm_vcpu *vcpu, void *addr, void *dest, unsigned int length)
+{
+	/* TODO: implement */
+	return false;
+}
+
+bool kvm_arch_vcpu_is_64bit(struct kvm_vcpu *vcpu)
+{
+	return !vcpu_mode_is_32bit(vcpu);
+}
 #endif
 
 static int kvm_vcpu_initialized(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9f18b06bb..17dea02b7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12904,6 +12904,24 @@ unsigned long kvm_arch_vcpu_get_ip(struct kvm_vcpu *vcpu)
 	return kvm_rip_read(vcpu);
 }
 
+unsigned long kvm_arch_vcpu_get_frame_pointer(struct kvm_vcpu *vcpu)
+{
+	return kvm_register_read_raw(vcpu, VCPU_REGS_RBP);
+}
+
+bool kvm_arch_vcpu_read_virt(struct kvm_vcpu *vcpu, void *addr, void *dest, unsigned int length)
+{
+	struct x86_exception e;
+
+	/* Return true on success */
+	return kvm_read_guest_virt(vcpu, addr, dest, length, &e) == X86EMUL_CONTINUE;
+}
+
+bool kvm_arch_vcpu_is_64bit(struct kvm_vcpu *vcpu)
+{
+	return is_64_bit_mode(vcpu);
+}
+
 int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
 {
 	return kvm_vcpu_exiting_guest_mode(vcpu) == IN_GUEST_MODE;
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index fb6c6109f..f92f1a9c8 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1595,6 +1595,10 @@ static inline bool kvm_arch_intc_initialized(struct kvm *kvm)
 
 #ifdef CONFIG_GUEST_PERF_EVENTS
 unsigned long kvm_arch_vcpu_get_ip(struct kvm_vcpu *vcpu);
+unsigned long kvm_arch_vcpu_get_frame_pointer(struct kvm_vcpu *vcpu);
+bool kvm_arch_vcpu_read_virt(struct kvm_vcpu *vcpu, void *addr, void *dest,
+			     unsigned int length);
+bool kvm_arch_vcpu_is_64bit(struct kvm_vcpu *vcpu);
 
 void kvm_register_perf_callbacks(unsigned int (*pt_intr_handler)(void));
 void kvm_unregister_perf_callbacks(void);
-- 
2.42.0