From: Christian Ehrhardt <ehrhardt@xxxxxxxxxxxxxxxxxx>
The current implementation of kvmtrace uses always a 64 bit cycle variable,
but get_cycles() which is used to fill it is "unsigned long" which might be 32
bit.
This reduces the accuracy e.g. on embedded powerpc since we would have a 64bit
value but get_cycle() only returns the low 32 bit.
To solve that this patch introduces kvm_arch_trace_cycles() which allows us
to make this calculation architecture aware. That way every architecture can
insert whatever fits best for their "kvmtrace cycle counter".
Signed-off-by: Christian Ehrhardt <ehrhardt@xxxxxxxxxxxxxxxxxx>
---
[diffstat]
arch/powerpc/kvm/powerpc.c | 25 +++++++++++++++++++++++++
arch/x86/kvm/x86.c | 5 +++++
include/linux/kvm_host.h | 2 ++
virt/kvm/kvm_trace.c | 2 +-
4 files changed, 33 insertions(+), 1 deletion(-)
[diff]
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -521,6 +521,31 @@
return r;
}
+/*
+ * We need a 64 bit value here and the default get_cycles has only 32bit (tbl)
+ * on 32bit ppc. Since we have a 64bit counter for that we provide it here in
+ * full resolution for the trace records.
+*/
+__u64 kvm_arch_trace_cycles()
+{
+ unsigned long ruval;
+ unsigned long ruval2;
+ unsigned long rlval;
+
+ /* get a consistant pair of upper/lower timebase (no wrap occured) */
+ asm volatile(
+ "loop:\n"
+ "mftbu %0\n"
+ "mftbl %1\n"
+ "mftbu %2\n"
+ "cmpw %0, %2\n"
+ "bne loop"
+ : "=r" (ruval), "=r" (rlval), "=r" (ruval2)
+ );
+
+ return (((__u64)ruval) << 32) | rlval;
+}
+
int kvm_arch_init(void *opaque)
{
return 0;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2458,6 +2458,11 @@
}
EXPORT_SYMBOL_GPL(kvm_emulate_pio_string);
+__u64 kvm_arch_trace_cycles()
+{
+ return get_cycles();
+}
+
int kvm_arch_init(void *opaque)
{
int r;
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -278,6 +278,8 @@
int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu);
void kvm_vcpu_kick(struct kvm_vcpu *vcpu);
+__u64 kvm_arch_trace_cycles(void);
+
static inline void kvm_guest_enter(void)
{
account_system_vtime(current);
diff --git a/virt/kvm/kvm_trace.c b/virt/kvm/kvm_trace.c
--- a/virt/kvm/kvm_trace.c
+++ b/virt/kvm/kvm_trace.c
@@ -74,7 +74,7 @@
| TRACE_REC_NUM_DATA_ARGS(extra);
if (p->cycle_in) {
- rec.u.cycle.cycle_u64 = get_cycles();
+ rec.u.cycle.cycle_u64 = kvm_arch_trace_cycles();
for (i = 0; i < extra; i++)
rec.u.cycle.extra_u32[i] = va_arg(*args, u32);
--
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