[RFC PATCH 2/2] KVM: arm64: export cntvoff in debugfs

[Nicolas Saenz Julienne]

While using cntvct as the raw clock for tracing, it's possible to
synchronize host/guest traces just by knowing the virtual offset applied
to the guest's virtual counter.

This is also the case on x86 when TSC is available. The offset is
exposed in debugfs as 'tsc-offset' on a per vcpu basis. So let's
implement the same for arm64.

Signed-off-by: Nicolas Saenz Julienne <nsaenzju@xxxxxxxxxx>
---
 arch/arm64/include/asm/kvm_host.h |  1 +
 arch/arm64/kvm/Makefile           |  2 +-
 arch/arm64/kvm/arch_timer.c       |  2 +-
 arch/arm64/kvm/debugfs.c          | 25 +++++++++++++++++++++++++
 include/kvm/arm_arch_timer.h      |  3 +++
 5 files changed, 31 insertions(+), 2 deletions(-)
 create mode 100644 arch/arm64/kvm/debugfs.c

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 2a5f7f38006f..130534c9079e 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -29,6 +29,7 @@
 #include <asm/thread_info.h>
 
 #define __KVM_HAVE_ARCH_INTC_INITIALIZED
+#define __KVM_HAVE_ARCH_VCPU_DEBUGFS
 
 #define KVM_HALT_POLL_NS_DEFAULT 500000
 
diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
index 989bb5dad2c8..17be7cf770f2 100644
--- a/arch/arm64/kvm/Makefile
+++ b/arch/arm64/kvm/Makefile
@@ -14,7 +14,7 @@ kvm-y := $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o $(KVM)/eventfd.o \
 	 $(KVM)/vfio.o $(KVM)/irqchip.o $(KVM)/binary_stats.o \
 	 arm.o mmu.o mmio.o psci.o perf.o hypercalls.o pvtime.o \
 	 inject_fault.o va_layout.o handle_exit.o \
-	 guest.o debug.o reset.o sys_regs.o \
+	 guest.o debug.o debugfs.o reset.o sys_regs.o \
 	 vgic-sys-reg-v3.o fpsimd.o pmu.o \
 	 arch_timer.o trng.o\
 	 vgic/vgic.o vgic/vgic-init.o \
diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
index 3df67c127489..ee69387f7fb6 100644
--- a/arch/arm64/kvm/arch_timer.c
+++ b/arch/arm64/kvm/arch_timer.c
@@ -82,7 +82,7 @@ u64 timer_get_cval(struct arch_timer_context *ctxt)
 	}
 }
 
-static u64 timer_get_offset(struct arch_timer_context *ctxt)
+u64 timer_get_offset(struct arch_timer_context *ctxt)
 {
 	struct kvm_vcpu *vcpu = ctxt->vcpu;
 
diff --git a/arch/arm64/kvm/debugfs.c b/arch/arm64/kvm/debugfs.c
new file mode 100644
index 000000000000..f0f5083ea8d4
--- /dev/null
+++ b/arch/arm64/kvm/debugfs.c
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2021 Red Hat Inc.
+ */
+
+#include <linux/kvm_host.h>
+#include <linux/debugfs.h>
+
+#include <kvm/arm_arch_timer.h>
+
+static int vcpu_get_cntv_offset(void *data, u64 *val)
+{
+	struct kvm_vcpu *vcpu = (struct kvm_vcpu *)data;
+
+	*val = timer_get_offset(vcpu_vtimer(vcpu));
+
+	return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(vcpu_cntvoff_fops, vcpu_get_cntv_offset, NULL, "%lld\n");
+
+void kvm_arch_create_vcpu_debugfs(struct kvm_vcpu *vcpu, struct dentry *debugfs_dentry)
+{
+	debugfs_create_file("cntvoff", 0444, debugfs_dentry, vcpu, &vcpu_cntvoff_fops);
+}
diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h
index 51c19381108c..de0cd9be825c 100644
--- a/include/kvm/arm_arch_timer.h
+++ b/include/kvm/arm_arch_timer.h
@@ -106,4 +106,7 @@ void kvm_arm_timer_write_sysreg(struct kvm_vcpu *vcpu,
 u32 timer_get_ctl(struct arch_timer_context *ctxt);
 u64 timer_get_cval(struct arch_timer_context *ctxt);
 
+/* Nedded for debugfs */
+u64 timer_get_offset(struct arch_timer_context *ctxt);
+
 #endif
-- 
2.33.1