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

1 files changed, 10 insertions, 13 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);
 	}
 }