From: kettenis <kettenis@openbsd.org>
Date: Tue, 11 May 2021 18:21:12 +0000 (+0000)
Subject: A Data Segment Interrupt does not indicate whether it was the result
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=2942dd665b2f5211be162d4dd1f187ed5277f9b7;p=openbsd

A Data Segment Interrupt does not indicate whether it was the result
of a read or a write fault.  Unfortunately that means we can't call
uvm_fault(), as we have to pass the right access_type.  In particular,
passing PROT_READ for write access on a write-only page will fail.
Fix this issue by inserting an appropriate SLB entry when a mapping
exists at the fault address.  A subsequent Data Storage Interrupt
will call uvm_fault() to insert a mapping for the page into the
page tables.

Fixes the sys/kern/fork-exit regress test.

Debugging done by bluhm@ and patrick@
ok bluhm@
---

diff --git a/sys/arch/powerpc64/include/pmap.h b/sys/arch/powerpc64/include/pmap.h
index 06d44eddb1a..a531278411b 100644
--- a/sys/arch/powerpc64/include/pmap.h
+++ b/sys/arch/powerpc64/include/pmap.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: pmap.h,v 1.15 2020/08/25 17:49:58 kettenis Exp $	*/
+/*	$OpenBSD: pmap.h,v 1.16 2021/05/11 18:21:12 kettenis Exp $	*/
 
 /*
  * Copyright (c) 2020 Mark Kettenis <kettenis@openbsd.org>
@@ -68,6 +68,7 @@ void	pmap_bootstrap(void);
 void	pmap_bootstrap_cpu(void);
 
 int	pmap_slbd_fault(pmap_t, vaddr_t);
+int	pmap_slbd_enter(pmap_t, vaddr_t);
 int	pmap_set_user_slb(pmap_t, vaddr_t, vaddr_t *, vsize_t *);
 void	pmap_clear_user_slb(void);
 void	pmap_unset_user_slb(void);
diff --git a/sys/arch/powerpc64/powerpc64/pmap.c b/sys/arch/powerpc64/powerpc64/pmap.c
index 04348c7a6f5..f18c919049e 100644
--- a/sys/arch/powerpc64/powerpc64/pmap.c
+++ b/sys/arch/powerpc64/powerpc64/pmap.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: pmap.c,v 1.55 2020/12/23 17:54:04 kettenis Exp $ */
+/*	$OpenBSD: pmap.c,v 1.56 2021/05/11 18:21:12 kettenis Exp $ */
 
 /*
  * Copyright (c) 2015 Martin Pieuchot
@@ -438,6 +438,20 @@ pmap_slbd_alloc(pmap_t pm, vaddr_t va)
 	return slbd;
 }
 
+int
+pmap_slbd_enter(pmap_t pm, vaddr_t va)
+{
+	struct slb_desc *slbd;
+
+	PMAP_VP_LOCK(pm);
+	slbd = pmap_slbd_lookup(pm, va);
+	if (slbd == NULL)
+		slbd = pmap_slbd_alloc(pm, va);
+	PMAP_VP_UNLOCK(pm);
+
+	return slbd ? 0 : EFAULT;
+}
+
 int
 pmap_set_user_slb(pmap_t pm, vaddr_t va, vaddr_t *kva, vsize_t *len)
 {
diff --git a/sys/arch/powerpc64/powerpc64/trap.c b/sys/arch/powerpc64/powerpc64/trap.c
index 1a7ccf04886..fdba2f0e325 100644
--- a/sys/arch/powerpc64/powerpc64/trap.c
+++ b/sys/arch/powerpc64/powerpc64/trap.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: trap.c,v 1.50 2021/05/05 07:29:01 mpi Exp $	*/
+/*	$OpenBSD: trap.c,v 1.51 2021/05/11 18:21:12 kettenis Exp $	*/
 
 /*
  * Copyright (c) 2020 Mark Kettenis <kettenis@openbsd.org>
@@ -53,6 +53,7 @@ trap(struct trapframe *frame)
 	int type = frame->exc;
 	union sigval sv;
 	struct vm_map *map;
+	struct vm_map_entry *entry;
 	pmap_t pm;
 	vaddr_t va;
 	int access_type;
@@ -123,7 +124,7 @@ trap(struct trapframe *frame)
 			va = curpcb->pcb_userva | (va & SEGMENT_MASK);
 		}
 		if (frame->dsisr & DSISR_STORE)
-			access_type = PROT_READ | PROT_WRITE;
+			access_type = PROT_WRITE;
 		else
 			access_type = PROT_READ;
 		error = uvm_fault(map, trunc_page(va), 0, access_type);
@@ -220,8 +221,33 @@ trap(struct trapframe *frame)
 		error = pmap_slbd_fault(pm, frame->dar);
 		if (error == 0)
 			break;
-		frame->dsisr = 0;
-		/* FALLTHROUGH */
+
+		if (!uvm_map_inentry(p, &p->p_spinentry, PROC_STACK(p),
+		    "[%s]%d/%d sp=%lx inside %lx-%lx: not MAP_STACK\n",
+		    uvm_map_inentry_sp, p->p_vmspace->vm_map.sserial))
+			goto out;
+
+		/*
+		 * Unfortunately, the hardware doesn't tell us whether
+		 * this was a read or a write fault.  So we check
+		 * whether there is a mapping at the fault address and
+		 * insert a new SLB entry.  Executing the faulting
+		 * instruction again should result in a Data Storage
+		 * Interrupt that does indicate whether we're dealing
+		 * with with a read or a write fault.
+		 */
+		map = &p->p_vmspace->vm_map;
+		vm_map_lock_read(map);
+		if (uvm_map_lookup_entry(map, frame->dar, &entry))
+			error = pmap_slbd_enter(pm, frame->dar);
+		else
+			error = EFAULT;
+		vm_map_unlock_read(map);
+		if (error) {
+			sv.sival_ptr = (void *)frame->dar;
+			trapsignal(p, SIGSEGV, 0, SEGV_MAPERR, sv);
+		}
+		break;
 
 	case EXC_DSI|EXC_USER:
 		if (!uvm_map_inentry(p, &p->p_spinentry, PROC_STACK(p),
@@ -232,7 +258,7 @@ trap(struct trapframe *frame)
 		map = &p->p_vmspace->vm_map;
 		va = frame->dar;
 		if (frame->dsisr & DSISR_STORE)
-			access_type = PROT_READ | PROT_WRITE;
+			access_type = PROT_WRITE;
 		else
 			access_type = PROT_READ;
 		error = uvm_fault(map, trunc_page(va), 0, access_type);