pc/pc64: keep shadow copy of DR7 in Mach and use that to check whether we need to reset DR7 in procsave(); remove superfluous reset of DR7 in mmurelease()

6 files changed, 17 insertions, 8 deletions

diff --git a/sys/src/9/pc/dat.h b/sys/src/9/pc/dat.h
index 14f406389..452b613da 100644
--- a/sys/src/9/pc/dat.h
+++ b/sys/src/9/pc/dat.h
@@ -258,6 +258,8 @@ struct Mach
 	uvlong	tscticks;
 	int	pdballoc;
 	int	pdbfree;
+	
+	u32int	dr7;			/* shadow copy of dr7 */
 
 	int	stack[1];
 };
diff --git a/sys/src/9/pc/main.c b/sys/src/9/pc/main.c
index bb4422325..e9ee24acc 100644
--- a/sys/src/9/pc/main.c
+++ b/sys/src/9/pc/main.c
@@ -844,8 +844,10 @@ procrestore(Proc *p)
 {
 	uvlong t;
 	
-	if(p->dr[7] != 0)
+	if(p->dr[7] != 0){
+		m->dr7 = p->dr[7];
 		putdr(p->dr);
+	}
 
 	if(p->kp)
 		return;
@@ -863,8 +865,11 @@ procsave(Proc *p)
 {
 	uvlong t;
 	
-	if(p->dr[7] != 0)
+	/* we could just always putdr7(0) but accessing DR7 might be slow in a VM */
+	if(m->dr7 != 0){
+		m->dr7 = 0;
 		putdr7(0);
+	}
 
 	cycles(&t);
 	p->kentry -= t;
diff --git a/sys/src/9/pc/mmu.c b/sys/src/9/pc/mmu.c
index dc8546f6f..2e77aaee7 100644
--- a/sys/src/9/pc/mmu.c
+++ b/sys/src/9/pc/mmu.c
@@ -387,8 +387,6 @@ mmurelease(Proc* proc)
 		proc->ldt = nil;
 		proc->nldt = 0;
 	}
-	if(proc->dr[7] != 0)
-		putdr7(0);
 }
 
 /*
diff --git a/sys/src/9/pc64/dat.h b/sys/src/9/pc64/dat.h
index 1f7a4717c..e942e51e9 100644
--- a/sys/src/9/pc64/dat.h
+++ b/sys/src/9/pc64/dat.h
@@ -223,6 +223,8 @@ struct Mach
 	int	havepge;
 	int	havewatchpt8;
 	uvlong	tscticks;
+	
+	u64int	dr7;			/* shadow copy of dr7 */
 
 	uintptr	stack[1];
 };
diff --git a/sys/src/9/pc64/main.c b/sys/src/9/pc64/main.c
index ea920fe56..24bb0d073 100644
--- a/sys/src/9/pc64/main.c
+++ b/sys/src/9/pc64/main.c
@@ -798,8 +798,10 @@ procrestore(Proc *p)
 {
 	uvlong t;
 	
-	if(p->dr[7] != 0)
+	if(p->dr[7] != 0){
+		m->dr7 = p->dr[7];
 		putdr(p->dr);
+	}
 
 	if(p->kp)
 		return;
@@ -814,8 +816,10 @@ procsave(Proc *p)
 {
 	uvlong t;
 	
-	if(p->dr[7] != 0)
+	if(m->dr7 != 0){
+		m->dr7 = 0;
 		putdr7(0);
+	}
 
 	cycles(&t);
 	p->kentry -= t;
diff --git a/sys/src/9/pc64/mmu.c b/sys/src/9/pc64/mmu.c
index 19828eafc..6f27ac25e 100644
--- a/sys/src/9/pc64/mmu.c
+++ b/sys/src/9/pc64/mmu.c
@@ -425,8 +425,6 @@ mmurelease(Proc *proc)
 		proc->kmapcount = proc->kmapindex = 0;
 	}
 	mmufree(proc);
-	if(proc->dr[7] != 0)
-		putdr7(0);
 	taskswitch((uintptr)m+MACHSIZE);
 }