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pc64: fix kmap() and invlpg()

flushing tlb once the index wraps arround is not enougth
as in use pte's can be speculatively loaded. so instead
use invlpg() and explicitely invalidate the tlb of the
page mapped.

this fixes wired mount cache corruption for reads approaching
2MB which is the size of the KMAP window.

invlpg() was broken, using wrong operand type.

--- a/sys/src/9/pc64/l.s

+++ b/sys/src/9/pc64/l.s

@@ -449,11 +449,8 @@

 	MOVQ	BP, AX				/* BP set to -1 if traped */

 	RET

-TEXT invlpg(SB), 1, $-4				/* INVLPG va+0(FP) */

-	MOVQ	RARG, va+0(FP)

-

-	INVLPG	va+0(FP)

-

+TEXT invlpg(SB), 1, $-4

+	INVLPG	(RARG)

 	RET

 TEXT wbinvd(SB), 1, $-4

--- a/sys/src/9/pc64/mmu.c

+++ b/sys/src/9/pc64/mmu.c

@@ -485,15 +485,13 @@

 		return (KMap*)KADDR(pa);

 	x = splhi();

-	va = KMAP + ((uintptr)up->kmapindex << PGSHIFT);

+	va = KMAP + (((uintptr)up->kmapindex++ << PGSHIFT) & (KMAPSIZE-1));

 	pte = mmuwalk(m->pml4, va, 0, 1);

-	if(pte == 0 || *pte & PTEVALID)

+	if(pte == 0 || (*pte & PTEVALID) != 0)

 		panic("kmap: pa=%#p va=%#p", pa, va);

 	*pte = pa | PTEWRITE|PTEVALID;

- 	up->kmapindex = (up->kmapindex + 1) % (1<<PTSHIFT);

-	if(up->kmapindex == 0)

-		mmuflushtlb();

 	splx(x);

+	invlpg(va);

 	return (KMap*)va;

 }