Deprecate the 3-way return values from vm_gla2gpa() and vm_copy_setup().

Prior to this change both functions returned 0 for success, -1 for failure
and +1 to indicate that an exception was injected into the guest.

The numerical value of ERESTART also happens to be -1 so when these functions
returned -1 it had to be translated to a positive errno value to prevent the
VM_RUN ioctl from being inadvertently restarted. This made it easy to introduce
bugs when writing emulation code.

Fix this by adding an 'int *guest_fault' parameter and setting it to '1' if
an exception was delivered to the guest. The return value is 0 or EFAULT so
no additional translation is needed.

Reviewed by:	tychon
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D2428

3 files changed, 76 insertions, 84 deletions

diff --git a/sys/amd64/vmm/vmm.c b/sys/amd64/vmm/vmm.c
index bca9b98..51c63f5 100644
--- a/sys/amd64/vmm/vmm.c
+++ b/sys/amd64/vmm/vmm.c
@@ -1256,7 +1256,7 @@ vm_handle_inst_emul(struct vm *vm, int vcpuid, bool *retu)
 	mem_region_read_t mread;
 	mem_region_write_t mwrite;
 	enum vm_cpu_mode cpu_mode;
-	int cs_d, error, length;
+	int cs_d, error, fault, length;
 
 	vcpu = &vm->vcpu[vcpuid];
 	vme = &vcpu->exitinfo;
@@ -1279,19 +1279,15 @@ vm_handle_inst_emul(struct vm *vm, int vcpuid, bool *retu)
 		 */
 		length = vme->inst_length ? vme->inst_length : VIE_INST_SIZE;
 		error = vmm_fetch_instruction(vm, vcpuid, paging, vme->rip +
-		    cs_base, length, vie);
+		    cs_base, length, vie, &fault);
 	} else {
 		/*
 		 * The instruction bytes have already been copied into 'vie'
 		 */
-		error = 0;
+		error = fault = 0;
 	}
-	if (error == 1)
-		return (0);		/* Resume guest to handle page fault */
-	else if (error == -1)
-		return (EFAULT);
-	else if (error != 0)
-		panic("%s: vmm_fetch_instruction error %d", __func__, error);
+	if (error || fault)
+		return (error);
 
 	if (vmm_decode_instruction(vm, vcpuid, gla, cpu_mode, cs_d, vie) != 0) {
 		VCPU_CTR1(vm, vcpuid, "Error decoding instruction at %#lx",
@@ -2323,7 +2319,7 @@ vm_copy_teardown(struct vm *vm, int vcpuid, struct vm_copyinfo *copyinfo,
 int
 vm_copy_setup(struct vm *vm, int vcpuid, struct vm_guest_paging *paging,
     uint64_t gla, size_t len, int prot, struct vm_copyinfo *copyinfo,
-    int num_copyinfo)
+    int num_copyinfo, int *fault)
 {
 	int error, idx, nused;
 	size_t n, off, remaining;
@@ -2336,8 +2332,8 @@ vm_copy_setup(struct vm *vm, int vcpuid, struct vm_guest_paging *paging,
 	remaining = len;
 	while (remaining > 0) {
 		KASSERT(nused < num_copyinfo, ("insufficient vm_copyinfo"));
-		error = vm_gla2gpa(vm, vcpuid, paging, gla, prot, &gpa);
-		if (error)
+		error = vm_gla2gpa(vm, vcpuid, paging, gla, prot, &gpa, fault);
+		if (error || *fault)
 			return (error);
 		off = gpa & PAGE_MASK;
 		n = min(remaining, PAGE_SIZE - off);
@@ -2359,8 +2355,9 @@ vm_copy_setup(struct vm *vm, int vcpuid, struct vm_guest_paging *paging,
 
 	if (idx != nused) {
 		vm_copy_teardown(vm, vcpuid, copyinfo, num_copyinfo);
-		return (-1);
+		return (EFAULT);
 	} else {
+		*fault = 0;
 		return (0);
 	}
 }
diff --git a/sys/amd64/vmm/vmm_dev.c b/sys/amd64/vmm/vmm_dev.c
index 5be99cb..e3e140a 100644
--- a/sys/amd64/vmm/vmm_dev.c
+++ b/sys/amd64/vmm/vmm_dev.c
@@ -441,19 +441,9 @@ vmmdev_ioctl(struct cdev *cdev, u_long cmd, caddr_t data, int fflag,
 		CTASSERT(PROT_EXEC == VM_PROT_EXECUTE);
 		gg = (struct vm_gla2gpa *)data;
 		error = vm_gla2gpa(sc->vm, gg->vcpuid, &gg->paging, gg->gla,
-		    gg->prot, &gg->gpa);
-		KASSERT(error == 0 || error == 1 || error == -1,
+		    gg->prot, &gg->gpa, &gg->fault);
+		KASSERT(error == 0 || error == EFAULT,
 		    ("%s: vm_gla2gpa unknown error %d", __func__, error));
-		if (error >= 0) {
-			/*
-			 * error = 0: the translation was successful
-			 * error = 1: a fault was injected into the guest
-			 */
-			gg->fault = error;
-			error = 0;
-		} else {
-			error = EFAULT;
-		}
 		break;
 	}
 	case VM_ACTIVATE_CPU:
diff --git a/sys/amd64/vmm/vmm_instruction_emul.c b/sys/amd64/vmm/vmm_instruction_emul.c
index c83f3e0..9c6158a 100644
--- a/sys/amd64/vmm/vmm_instruction_emul.c
+++ b/sys/amd64/vmm/vmm_instruction_emul.c
@@ -597,13 +597,11 @@ emulate_movx(void *vm, int vcpuid, uint64_t gpa, struct vie *vie,
 
 /*
  * Helper function to calculate and validate a linear address.
- *
- * Returns 0 on success and 1 if an exception was injected into the guest.
  */
 static int
 get_gla(void *vm, int vcpuid, struct vie *vie, struct vm_guest_paging *paging,
     int opsize, int addrsize, int prot, enum vm_reg_name seg,
-    enum vm_reg_name gpr, uint64_t *gla)
+    enum vm_reg_name gpr, uint64_t *gla, int *fault)
 {
 	struct seg_desc desc;
 	uint64_t cr0, val, rflags;
@@ -629,7 +627,7 @@ get_gla(void *vm, int vcpuid, struct vie *vie, struct vm_guest_paging *paging,
 			vm_inject_ss(vm, vcpuid, 0);
 		else
 			vm_inject_gp(vm, vcpuid);
-		return (1);
+		goto guest_fault;
 	}
 
 	if (vie_canonical_check(paging->cpu_mode, *gla)) {
@@ -637,14 +635,19 @@ get_gla(void *vm, int vcpuid, struct vie *vie, struct vm_guest_paging *paging,
 			vm_inject_ss(vm, vcpuid, 0);
 		else
 			vm_inject_gp(vm, vcpuid);
-		return (1);
+		goto guest_fault;
 	}
 
 	if (vie_alignment_check(paging->cpl, opsize, cr0, rflags, *gla)) {
 		vm_inject_ac(vm, vcpuid, 0);
-		return (1);
+		goto guest_fault;
 	}
 
+	*fault = 0;
+	return (0);
+
+guest_fault:
+	*fault = 1;
 	return (0);
 }
 
@@ -660,7 +663,7 @@ emulate_movs(void *vm, int vcpuid, uint64_t gpa, struct vie *vie,
 #endif
 	uint64_t dstaddr, srcaddr, dstgpa, srcgpa, val;
 	uint64_t rcx, rdi, rsi, rflags;
-	int error, opsize, seg, repeat;
+	int error, fault, opsize, seg, repeat;
 
 	opsize = (vie->op.op_byte == 0xA4) ? 1 : vie->opsize;
 	val = 0;
@@ -683,8 +686,10 @@ emulate_movs(void *vm, int vcpuid, uint64_t gpa, struct vie *vie,
 		 * The count register is %rcx, %ecx or %cx depending on the
 		 * address size of the instruction.
 		 */
-		if ((rcx & vie_size2mask(vie->addrsize)) == 0)
-			return (0);
+		if ((rcx & vie_size2mask(vie->addrsize)) == 0) {
+			error = 0;
+			goto done;
+		}
 	}
 
 	/*
@@ -705,13 +710,16 @@ emulate_movs(void *vm, int vcpuid, uint64_t gpa, struct vie *vie,
 
 	seg = vie->segment_override ? vie->segment_register : VM_REG_GUEST_DS;
 	error = get_gla(vm, vcpuid, vie, paging, opsize, vie->addrsize,
-	    PROT_READ, seg, VM_REG_GUEST_RSI, &srcaddr);
-	if (error)
+	    PROT_READ, seg, VM_REG_GUEST_RSI, &srcaddr, &fault);
+	if (error || fault)
 		goto done;
 
 	error = vm_copy_setup(vm, vcpuid, paging, srcaddr, opsize, PROT_READ,
-	    copyinfo, nitems(copyinfo));
+	    copyinfo, nitems(copyinfo), &fault);
 	if (error == 0) {
+		if (fault)
+			goto done;	/* Resume guest to handle fault */
+
 		/*
 		 * case (2): read from system memory and write to mmio.
 		 */
@@ -720,11 +728,6 @@ emulate_movs(void *vm, int vcpuid, uint64_t gpa, struct vie *vie,
 		error = memwrite(vm, vcpuid, gpa, val, opsize, arg);
 		if (error)
 			goto done;
-	} else if (error > 0) {
-		/*
-		 * Resume guest execution to handle fault.
-		 */
-		goto done;
 	} else {
 		/*
 		 * 'vm_copy_setup()' is expected to fail for cases (3) and (4)
@@ -732,13 +735,17 @@ emulate_movs(void *vm, int vcpuid, uint64_t gpa, struct vie *vie,
 		 */
 
 		error = get_gla(vm, vcpuid, vie, paging, opsize, vie->addrsize,
-		    PROT_WRITE, VM_REG_GUEST_ES, VM_REG_GUEST_RDI, &dstaddr);
-		if (error)
+		    PROT_WRITE, VM_REG_GUEST_ES, VM_REG_GUEST_RDI, &dstaddr,
+		    &fault);
+		if (error || fault)
 			goto done;
 
 		error = vm_copy_setup(vm, vcpuid, paging, dstaddr, opsize,
-		    PROT_WRITE, copyinfo, nitems(copyinfo));
+		    PROT_WRITE, copyinfo, nitems(copyinfo), &fault);
 		if (error == 0) {
+			if (fault)
+				goto done;    /* Resume guest to handle fault */
+
 			/*
 			 * case (3): read from MMIO and write to system memory.
 			 *
@@ -754,27 +761,29 @@ emulate_movs(void *vm, int vcpuid, uint64_t gpa, struct vie *vie,
 
 			vm_copyout(vm, vcpuid, &val, copyinfo, opsize);
 			vm_copy_teardown(vm, vcpuid, copyinfo, nitems(copyinfo));
-		} else if (error > 0) {
-			/*
-			 * Resume guest execution to handle fault.
-			 */
-			goto done;
 		} else {
 			/*
 			 * Case (4): read from and write to mmio.
+			 *
+			 * Commit to the MMIO read/write (with potential
+			 * side-effects) only after we are sure that the
+			 * instruction is not going to be restarted due
+			 * to address translation faults.
 			 */
 			error = vm_gla2gpa(vm, vcpuid, paging, srcaddr,
-			    PROT_READ, &srcgpa);
-			if (error)
-				goto done;
-			error = memread(vm, vcpuid, srcgpa, &val, opsize, arg);
-			if (error)
+			    PROT_READ, &srcgpa, &fault);
+			if (error || fault)
 				goto done;
 
 			error = vm_gla2gpa(vm, vcpuid, paging, dstaddr,
-			   PROT_WRITE, &dstgpa);
+			   PROT_WRITE, &dstgpa, &fault);
+			if (error || fault)
+				goto done;
+
+			error = memread(vm, vcpuid, srcgpa, &val, opsize, arg);
 			if (error)
 				goto done;
+
 			error = memwrite(vm, vcpuid, dstgpa, val, opsize, arg);
 			if (error)
 				goto done;
@@ -819,10 +828,9 @@ emulate_movs(void *vm, int vcpuid, uint64_t gpa, struct vie *vie,
 			vm_restart_instruction(vm, vcpuid);
 	}
 done:
-	if (error < 0)
-		return (EFAULT);
-	else
-		return (0);
+	KASSERT(error == 0 || error == EFAULT, ("%s: unexpected error %d",
+	    __func__, error));
+	return (error);
 }
 
 static int
@@ -1185,7 +1193,7 @@ emulate_stack_op(void *vm, int vcpuid, uint64_t mmio_gpa, struct vie *vie,
 #endif
 	struct seg_desc ss_desc;
 	uint64_t cr0, rflags, rsp, stack_gla, val;
-	int error, size, stackaddrsize, pushop;
+	int error, fault, size, stackaddrsize, pushop;
 
 	val = 0;
 	size = vie->opsize;
@@ -1251,18 +1259,10 @@ emulate_stack_op(void *vm, int vcpuid, uint64_t mmio_gpa, struct vie *vie,
 	}
 
 	error = vm_copy_setup(vm, vcpuid, paging, stack_gla, size,
-	    pushop ? PROT_WRITE : PROT_READ, copyinfo, nitems(copyinfo));
-	if (error == -1) {
-		/*
-		 * XXX cannot return a negative error value here because it
-		 * ends up being the return value of the VM_RUN() ioctl and
-		 * is interpreted as a pseudo-error (for e.g. ERESTART).
-		 */
-		return (EFAULT);
-	} else if (error == 1) {
-		/* Resume guest execution to handle page fault */
-		return (0);
-	}
+	    pushop ? PROT_WRITE : PROT_READ, copyinfo, nitems(copyinfo),
+	    &fault);
+	if (error || fault)
+		return (error);
 
 	if (pushop) {
 		error = memread(vm, vcpuid, mmio_gpa, &val, size, arg);
@@ -1672,7 +1672,7 @@ ptp_hold(struct vm *vm, vm_paddr_t ptpphys, size_t len, void **cookie)
 
 int
 vm_gla2gpa(struct vm *vm, int vcpuid, struct vm_guest_paging *paging,
-    uint64_t gla, int prot, uint64_t *gpa)
+    uint64_t gla, int prot, uint64_t *gpa, int *guest_fault)
 {
 	int nlevels, pfcode, ptpshift, ptpindex, retval, usermode, writable;
 	u_int retries;
@@ -1680,6 +1680,8 @@ vm_gla2gpa(struct vm *vm, int vcpuid, struct vm_guest_paging *paging,
 	uint32_t *ptpbase32, pte32;
 	void *cookie;
 
+	*guest_fault = 0;
+
 	usermode = (paging->cpl == 3 ? 1 : 0);
 	writable = prot & VM_PROT_WRITE;
 	cookie = NULL;
@@ -1842,18 +1844,20 @@ restart:
 	*gpa = pte | (gla & (pgsize - 1));
 done:
 	ptp_release(&cookie);
+	KASSERT(retval == 0 || retval == EFAULT, ("%s: unexpected retval %d",
+	    __func__, retval));
 	return (retval);
 error:
-	retval = -1;
+	retval = EFAULT;
 	goto done;
 fault:
-	retval = 1;
+	*guest_fault = 1;
 	goto done;
 }
 
 int
 vmm_fetch_instruction(struct vm *vm, int vcpuid, struct vm_guest_paging *paging,
-    uint64_t rip, int inst_length, struct vie *vie)
+    uint64_t rip, int inst_length, struct vie *vie, int *faultptr)
 {
 	struct vm_copyinfo copyinfo[2];
 	int error, prot;
@@ -1863,13 +1867,14 @@ vmm_fetch_instruction(struct vm *vm, int vcpuid, struct vm_guest_paging *paging,
 
 	prot = PROT_READ | PROT_EXEC;
 	error = vm_copy_setup(vm, vcpuid, paging, rip, inst_length, prot,
-	    copyinfo, nitems(copyinfo));
-	if (error == 0) {
-		vm_copyin(vm, vcpuid, copyinfo, vie->inst, inst_length);
-		vm_copy_teardown(vm, vcpuid, copyinfo, nitems(copyinfo));
-		vie->num_valid = inst_length;
-	}
-	return (error);
+	    copyinfo, nitems(copyinfo), faultptr);
+	if (error || *faultptr)
+		return (error);
+
+	vm_copyin(vm, vcpuid, copyinfo, vie->inst, inst_length);
+	vm_copy_teardown(vm, vcpuid, copyinfo, nitems(copyinfo));
+	vie->num_valid = inst_length;
+	return (0);
 }
 
 static int