[PATCH 1/9] kvmtrace: Remove use of bit fields in kvm trace structure v3

[ehrhardt@xxxxxxxxxxxxxxxxxx]

From: Christian Ehrhardt <ehrhardt@xxxxxxxxxxxxxxxxxx>
From: Jerone Young <jyoung5@xxxxxxxxxx>

This patch fixes kvmtrace use on big endian systems. When using bit fields the
compiler will lay data out in the wrong order expected when laid down into a
file.
This fixes it by using one variable instead of using bit fields.

Updates in v3:
	- fixed macro definition bug in v2
	- ensured in macro operator order
	- fixed whitespace/indent issues
	- removed superfluous initialization

Signed-off-by: Jerone Young <jyoung5@xxxxxxxxxx>
Signed-off-by: Christian Ehrhardt <ehrhardt@xxxxxxxxxxxxxxxxxx>
---

[diffstat]
 include/linux/kvm.h  |   17 ++++++++++++++---
 virt/kvm/kvm_trace.c |   19 ++++++++++---------
 2 files changed, 24 insertions(+), 12 deletions(-)

[diff]

diff --git a/include/linux/kvm.h b/include/linux/kvm.h
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -311,9 +311,13 @@
 
 /* This structure represents a single trace buffer record. */
 struct kvm_trace_rec {
-	__u32 event:28;
-	__u32 extra_u32:3;
-	__u32 cycle_in:1;
+	/* variable rec_val
+	 * is split into:
+	 * bits 0 - 27  -> event id
+	 * bits 28 -30  -> number of extra data args of size u32
+	 * bits 31      -> binary indicator for if tsc is in record
+	 */
+	__u32 rec_val;
 	__u32 pid;
 	__u32 vcpu_id;
 	union {
@@ -326,6 +330,13 @@
 		} nocycle;
 	} u;
 } __attribute__((packed));
+
+#define TRACE_REC_EVENT_ID(val) \
+		(0x0fffffff & (val))
+#define TRACE_REC_NUM_DATA_ARGS(val) \
+		(0x70000000 & ((val) << 28))
+#define TRACE_REC_TCS(val) \
+		(0x80000000 & ((val) << 31))
 
 #define KVMIO 0xAE
 
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
@@ -54,12 +54,13 @@
 	struct kvm_trace *kt = kvm_trace;
 	struct kvm_trace_rec rec;
 	struct kvm_vcpu *vcpu;
-	int    i, extra, size;
+	int    i, size;
+	u32    extra;
 
 	if (unlikely(kt->trace_state != KVM_TRACE_STATE_RUNNING))
 		return;
 
-	rec.event	= va_arg(*args, u32);
+	rec.rec_val	= TRACE_REC_EVENT_ID(va_arg(*args, u32));
 	vcpu		= va_arg(*args, struct kvm_vcpu *);
 	rec.pid		= current->tgid;
 	rec.vcpu_id	= vcpu->vcpu_id;
@@ -67,21 +68,21 @@
 	extra   	= va_arg(*args, u32);
 	WARN_ON(!(extra <= KVM_TRC_EXTRA_MAX));
 	extra 		= min_t(u32, extra, KVM_TRC_EXTRA_MAX);
-	rec.extra_u32   = extra;
 
-	rec.cycle_in 	= p->cycle_in;
-
-	if (rec.cycle_in) {
+	rec.rec_val |= TRACE_REC_TCS(p->cycle_in)
+			| TRACE_REC_NUM_DATA_ARGS(extra);
+	
+	if (p->cycle_in) {
 		rec.u.cycle.cycle_u64 = get_cycles();
 
-		for (i = 0; i < rec.extra_u32; i++)
+		for (i = 0; i < extra; i++)
 			rec.u.cycle.extra_u32[i] = va_arg(*args, u32);
 	} else {
-		for (i = 0; i < rec.extra_u32; i++)
+		for (i = 0; i < extra; i++)
 			rec.u.nocycle.extra_u32[i] = va_arg(*args, u32);
 	}
 
-	size = calc_rec_size(rec.cycle_in, rec.extra_u32 * sizeof(u32));
+	size = calc_rec_size(p->cycle_in, extra * sizeof(u32));
 	relay_write(kt->rchan, &rec, size);
 }
 
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