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

2 files changed, 19 insertions, 26 deletions

diff --git a/lib/libvmmapi/vmmapi.c b/lib/libvmmapi/vmmapi.c
index 0c15845..1e6e627 100644
--- a/lib/libvmmapi/vmmapi.c
+++ b/lib/libvmmapi/vmmapi.c
@@ -40,6 +40,7 @@ __FBSDID("$FreeBSD$");
 #include <machine/specialreg.h>
 #include <machine/param.h>
 
+#include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <assert.h>
@@ -958,9 +959,9 @@ vm_get_hpet_capabilities(struct vmctx *ctx, uint32_t *capabilities)
 	return (error);
 }
 
-static int
-gla2gpa(struct vmctx *ctx, int vcpu, struct vm_guest_paging *paging,
-    uint64_t gla, int prot, int *fault, uint64_t *gpa)
+int
+vm_gla2gpa(struct vmctx *ctx, int vcpu, struct vm_guest_paging *paging,
+    uint64_t gla, int prot, uint64_t *gpa, int *fault)
 {
 	struct vm_gla2gpa gg;
 	int error;
@@ -979,29 +980,18 @@ gla2gpa(struct vmctx *ctx, int vcpu, struct vm_guest_paging *paging,
 	return (error);
 }
 
-int
-vm_gla2gpa(struct vmctx *ctx, int vcpu, struct vm_guest_paging *paging,
-    uint64_t gla, int prot, uint64_t *gpa)
-{
-	int error, fault;
-
-	error = gla2gpa(ctx, vcpu, paging, gla, prot, &fault, gpa);
-	if (fault)
-		error = fault;
-	return (error);
-}
-
 #ifndef min
 #define	min(a,b)	(((a) < (b)) ? (a) : (b))
 #endif
 
 int
 vm_copy_setup(struct vmctx *ctx, int vcpu, struct vm_guest_paging *paging,
-    uint64_t gla, size_t len, int prot, struct iovec *iov, int iovcnt)
+    uint64_t gla, size_t len, int prot, struct iovec *iov, int iovcnt,
+    int *fault)
 {
 	void *va;
 	uint64_t gpa;
-	int error, fault, i, n, off;
+	int error, i, n, off;
 
 	for (i = 0; i < iovcnt; i++) {
 		iov[i].iov_base = 0;
@@ -1010,18 +1000,16 @@ vm_copy_setup(struct vmctx *ctx, int vcpu, struct vm_guest_paging *paging,
 
 	while (len) {
 		assert(iovcnt > 0);
-		error = gla2gpa(ctx, vcpu, paging, gla, prot, &fault, &gpa);
-		if (error)
-			return (-1);
-		if (fault)
-			return (1);
+		error = vm_gla2gpa(ctx, vcpu, paging, gla, prot, &gpa, fault);
+		if (error || *fault)
+			return (error);
 
 		off = gpa & PAGE_MASK;
 		n = min(len, PAGE_SIZE - off);
 
 		va = vm_map_gpa(ctx, gpa, n);
 		if (va == NULL)
-			return (-1);
+			return (EFAULT);
 
 		iov->iov_base = va;
 		iov->iov_len = n;
diff --git a/lib/libvmmapi/vmmapi.h b/lib/libvmmapi/vmmapi.h
index d001cd8..d3ecdc4 100644
--- a/lib/libvmmapi/vmmapi.h
+++ b/lib/libvmmapi/vmmapi.h
@@ -64,7 +64,7 @@ int	vm_setup_memory(struct vmctx *ctx, size_t len, enum vm_mmap_style s);
 void	*vm_map_gpa(struct vmctx *ctx, vm_paddr_t gaddr, size_t len);
 int	vm_get_gpa_pmap(struct vmctx *, uint64_t gpa, uint64_t *pte, int *num);
 int	vm_gla2gpa(struct vmctx *, int vcpuid, struct vm_guest_paging *paging,
-		   uint64_t gla, int prot, uint64_t *gpa);
+		   uint64_t gla, int prot, uint64_t *gpa, int *fault);
 uint32_t vm_get_lowmem_limit(struct vmctx *ctx);
 void	vm_set_lowmem_limit(struct vmctx *ctx, uint32_t limit);
 void	vm_set_memflags(struct vmctx *ctx, int flags);
@@ -131,10 +131,15 @@ int	vm_get_hpet_capabilities(struct vmctx *ctx, uint32_t *capabilities);
 /*
  * Translate the GLA range [gla,gla+len) into GPA segments in 'iov'.
  * The 'iovcnt' should be big enough to accomodate all GPA segments.
- * Returns 0 on success, 1 on a guest fault condition and -1 otherwise.
+ *
+ * retval	fault		Interpretation
+ *   0		  0		Success
+ *   0		  1		An exception was injected into the guest
+ * EFAULT	 N/A		Error
  */
 int	vm_copy_setup(struct vmctx *ctx, int vcpu, struct vm_guest_paging *pg,
-	    uint64_t gla, size_t len, int prot, struct iovec *iov, int iovcnt);
+	    uint64_t gla, size_t len, int prot, struct iovec *iov, int iovcnt,
+	    int *fault);
 void	vm_copyin(struct vmctx *ctx, int vcpu, struct iovec *guest_iov,
 	    void *host_dst, size_t len);
 void	vm_copyout(struct vmctx *ctx, int vcpu, const void *host_src,