[PATCH] [v2] Remove use of bit fields in kvm trace structure

[PATCH] [v2] Remove use of bit fields in kvm trace structure

[Jerone Young]

2 files changed, 30 insertions(+), 11 deletions(-)
include/linux/kvm.h  |   17 ++++++++++++++---
virt/kvm/kvm_trace.c |   24 ++++++++++++++++--------


 *Updates:
	Create global definitions for setting trace records as opposed to
	explicitly setting them inside of a function.

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.

Signed-off-by: Jerone Young <jyoung5@us.ibm.com>

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 @@ struct kvm_s390_interrupt {
 
 /* 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 @@ struct kvm_trace_rec {
 		} 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 +54,17 @@ static void kvm_add_trace(void *probe_pr
 	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 = 0;
+	
+	/* set event id */	
+	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 +72,24 @@ static void kvm_add_trace(void *probe_pr
 	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;
+	/* set inidicator for tcs record */
+	rec.rec_val 	|= TRACE_REC_TCS(p->cycle_in);
 
-	if (rec.cycle_in) {
+	/* set extra data num */
+	rec.rec_val     |= 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);
 }
 

Re: [PATCH] [v2] Remove use of bit fields in kvm trace structure

[Hollis Blanchard]

On Tue, 2008-06-24 at 13:54 -0500, Jerone Young wrote:
> 2 files changed, 30 insertions(+), 11 deletions(-)
> include/linux/kvm.h  |   17 ++++++++++++++---
> virt/kvm/kvm_trace.c |   24 ++++++++++++++++--------
> 
> 
>  *Updates:
> 	Create global definitions for setting trace records as opposed to
> 	explicitly setting them inside of a function.
> 
> 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.
> 
> Signed-off-by: Jerone Young <jyoung5@us.ibm.com>

Acked-by: Hollis Blanchard <hollisb@us.ibm.com>

Avi, if this is OK now, please also apply Jerone's earlier patches:
	[PATCH 2 of 3] Move KVM TRACE DEFINITIONS to common header
	[PATCH 3 of 3] Add new KVM TRACE events
(and add my Acked-by to those as well).

-- 
Hollis Blanchard
IBM Linux Technology Center

Re: [PATCH] [v2] Remove use of bit fields in kvm trace structure

[Avi Kivity]

Hollis Blanchard wrote:
> Avi, if this is OK now, please also apply Jerone's earlier patches:
> 	[PATCH 2 of 3] Move KVM TRACE DEFINITIONS to common header
> 	[PATCH 3 of 3] Add new KVM TRACE events
> (and add my Acked-by to those as well).
>
>   

I've lost the thread, so please repost any missing patches.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.