gorka should get the credit for this.  he did this years ago, but it was
so ugly i was trying to avoid it.  vbox seems not to emulate hardware
very well.

Reference: /n/atom/patch/applied/vboxmmu
Date: Tue Apr 22 15:37:37 CES 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/k10/mmu.c	Tue Apr 22 15:37:04 2014
+++ /sys/src/nix/k10/mmu.c	Tue Apr 22 15:37:05 2014
@@ -87,7 +87,7 @@
 }
 
 void
-mmuflushtlb(uintmem)
+xmmuflushtlb(uintmem)
 {
 
 	m->tlbpurge++;
@@ -98,6 +98,24 @@
 	putcr3(m->pml4->pa);
 }
 
+/* hack for vbox */
+void
+mmuflushtlb(uintmem)
+{
+	int i;
+	PTE *pte;
+
+	m->tlbpurge++;
+	if(m->pml4->daddr){
+		pte = UINT2PTR(m->pml4->va);
+		for(i = 0; i < m->pml4->daddr; i++)
+			if(pte[i] & PteP)
+				pte[i] = 0;
+		m->pml4->daddr = 0;
+	}
+	putcr3(m->pml4->pa);
+}
+
 void
 mmuflush(void)
 {
@@ -259,6 +277,7 @@
 void
 mmuswitch(Proc* proc)
 {
+	int i;
 	PTE *pte;
 	Page *page;
 	Mpl pl;
@@ -270,7 +289,12 @@
 	}
 
 	if(m->pml4->daddr){
-		memset(UINT2PTR(m->pml4->va), 0, m->pml4->daddr*sizeof(PTE));
+		/* hack for vbox */
+//		memset(UINT2PTR(m->pml4->va), 0, m->pml4->daddr*sizeof(PTE));
+		pte = UINT2PTR(m->pml4->va);
+		for(i = 0; i < m->pml4->daddr; i++)
+			if(pte[i] & PteP)
+				pte[i] = 0;
 		m->pml4->daddr = 0;
 	}