From 97c14dba6f96234c7120802f9d727a4ccfd17367 Mon Sep 17 00:00:00 2001
From: Vincent Donnefort <vdonnefort@google.com>
Date: Wed, 11 Sep 2024 10:30:22 +0100
Subject: [PATCH] FROMLIST: KVM: arm64: Add clock support in the nVHE hyp

By default, the arm64 host kernel is using the arch timer as a source
for sched_clock. Conveniently, EL2 has access to that same counter,
allowing to generate clock values that are synchronized.

The clock needs nonetheless to be setup with the same slope values as
the kernel. Introducing at the same time trace_clock() which is expected
to be later configured by the hypervisor tracing.

Bug: 357781595
Link: https://lore.kernel.org/all/20240911093029.3279154-7-vdonnefort@google.com/
Change-Id: I19ce77211afed371c3362cdd6f43c0ca1d3592bb
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
---
 arch/arm64/include/asm/kvm_hyp.h        |  1 -
 arch/arm64/kvm/hyp/include/nvhe/clock.h | 16 ++++++++
 arch/arm64/kvm/hyp/nvhe/Makefile        |  1 +
 arch/arm64/kvm/hyp/nvhe/clock.c         | 49 +++++++++++++++++++++++++
 4 files changed, 66 insertions(+), 1 deletion(-)
 create mode 100644 arch/arm64/kvm/hyp/include/nvhe/clock.h
 create mode 100644 arch/arm64/kvm/hyp/nvhe/clock.c

diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
index aadb9a9500dc..c83f8d39d15a 100644
--- a/arch/arm64/include/asm/kvm_hyp.h
+++ b/arch/arm64/include/asm/kvm_hyp.h
@@ -147,5 +147,4 @@ extern u64 kvm_nvhe_sym(id_aa64smfr0_el1_sys_val);
 extern unsigned long kvm_nvhe_sym(__icache_flags);
 extern unsigned int kvm_nvhe_sym(kvm_arm_vmid_bits);
 extern unsigned int kvm_nvhe_sym(kvm_host_sve_max_vl);
-
 #endif /* __ARM64_KVM_HYP_H__ */
diff --git a/arch/arm64/kvm/hyp/include/nvhe/clock.h b/arch/arm64/kvm/hyp/include/nvhe/clock.h
new file mode 100644
index 000000000000..2bd05b3b89f9
--- /dev/null
+++ b/arch/arm64/kvm/hyp/include/nvhe/clock.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ARM64_KVM_HYP_NVHE_CLOCK_H
+#define __ARM64_KVM_HYP_NVHE_CLOCK_H
+#include <linux/types.h>
+
+#include <asm/kvm_hyp.h>
+
+#ifdef CONFIG_TRACING
+void trace_clock_update(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc);
+u64 trace_clock(void);
+#else
+static inline void
+trace_clock_update(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc) { }
+static inline u64 trace_clock(void) { return 0; }
+#endif
+#endif
diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
index b43426a493df..323e992089bd 100644
--- a/arch/arm64/kvm/hyp/nvhe/Makefile
+++ b/arch/arm64/kvm/hyp/nvhe/Makefile
@@ -28,6 +28,7 @@ hyp-obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o hyp-init.o host.o
 hyp-obj-y += ../vgic-v3-sr.o ../aarch32.o ../vgic-v2-cpuif-proxy.o ../entry.o \
 	 ../fpsimd.o ../hyp-entry.o ../exception.o ../pgtable.o
 hyp-obj-$(CONFIG_LIST_HARDENED) += list_debug.o
+hyp-obj-$(CONFIG_TRACING) += clock.o
 hyp-obj-y += $(lib-objs)
 
 ##
diff --git a/arch/arm64/kvm/hyp/nvhe/clock.c b/arch/arm64/kvm/hyp/nvhe/clock.c
new file mode 100644
index 000000000000..0d1f74bc2e11
--- /dev/null
+++ b/arch/arm64/kvm/hyp/nvhe/clock.c
@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2024 Google LLC
+ * Author: Vincent Donnefort <vdonnefort@google.com>
+ */
+
+#include <nvhe/clock.h>
+
+#include <asm/arch_timer.h>
+#include <asm/div64.h>
+
+static struct clock_data {
+	struct {
+		u32 mult;
+		u32 shift;
+		u64 epoch_ns;
+		u64 epoch_cyc;
+	} data[2];
+	u64 cur;
+} trace_clock_data;
+
+/* Does not guarantee no reader on the modified bank. */
+void trace_clock_update(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc)
+{
+	struct clock_data *clock = &trace_clock_data;
+	u64 bank = clock->cur ^ 1;
+
+	clock->data[bank].mult		= mult;
+	clock->data[bank].shift		= shift;
+	clock->data[bank].epoch_ns	= epoch_ns;
+	clock->data[bank].epoch_cyc	= epoch_cyc;
+
+	smp_store_release(&clock->cur, bank);
+}
+
+/* Using host provided data. Do not use for anything else than debugging. */
+u64 trace_clock(void)
+{
+	struct clock_data *clock = &trace_clock_data;
+	u64 bank = smp_load_acquire(&clock->cur);
+	u64 cyc, ns;
+
+	cyc = __arch_counter_get_cntpct() - clock->data[bank].epoch_cyc;
+
+	ns = cyc * clock->data[bank].mult;
+	ns >>= clock->data[bank].shift;
+
+	return (u64)ns + clock->data[bank].epoch_ns;
+}