svn commit: r362600 - in head: sys/amd64/include sys/amd64/vmm usr.sbin/bhyve

[Conrad Meyer]

Author: cem
Date: Thu Jun 25 00:18:42 2020
New Revision: 362600
URL: https://svnweb.freebsd.org/changeset/base/362600

Log:
  bhyve(8): For prototyping, reattempt decode in userspace
  
  If userspace has a newer bhyve than the kernel, it may be able to decode
  and emulate some instructions vmm.ko is unaware of.  In this scenario,
  reset decoder state and try again.
  
  Reviewed by:	grehan
  Differential Revision:	https://reviews.freebsd.org/D24464

Modified:
  head/sys/amd64/include/vmm.h
  head/sys/amd64/include/vmm_instruction_emul.h
  head/sys/amd64/vmm/vmm_instruction_emul.c
  head/usr.sbin/bhyve/bhyverun.c

Modified: head/sys/amd64/include/vmm.h
==============================================================================
--- head/sys/amd64/include/vmm.h	Thu Jun 25 00:09:43 2020	(r362599)
+++ head/sys/amd64/include/vmm.h	Thu Jun 25 00:18:42 2020	(r362600)
@@ -546,6 +546,9 @@ _Static_assert(_Alignof(struct vie_op) == 2, "ABI");
 struct vie {
 	uint8_t		inst[VIE_INST_SIZE];	/* instruction bytes */
 	uint8_t		num_valid;		/* size of the instruction */
+
+/* The following fields are all zeroed upon restart. */
+#define	vie_startzero	num_processed
 	uint8_t		num_processed;
 
 	uint8_t		addrsize:4, opsize:4;	/* address and operand sizes */

Modified: head/sys/amd64/include/vmm_instruction_emul.h
==============================================================================
--- head/sys/amd64/include/vmm_instruction_emul.h	Thu Jun 25 00:09:43 2020	(r362599)
+++ head/sys/amd64/include/vmm_instruction_emul.h	Thu Jun 25 00:18:42 2020	(r362600)
@@ -105,6 +105,7 @@ int vm_gla2gpa_nofault(struct vm *vm, int vcpuid, stru
     uint64_t gla, int prot, uint64_t *gpa, int *is_fault);
 #endif /* _KERNEL */
 
+void vie_restart(struct vie *vie);
 void vie_init(struct vie *vie, const char *inst_bytes, int inst_length);
 
 /*

Modified: head/sys/amd64/vmm/vmm_instruction_emul.c
==============================================================================
--- head/sys/amd64/vmm/vmm_instruction_emul.c	Thu Jun 25 00:09:43 2020	(r362599)
+++ head/sys/amd64/vmm/vmm_instruction_emul.c	Thu Jun 25 00:18:42 2020	(r362600)
@@ -53,7 +53,9 @@ __FBSDID("$FreeBSD$");
 #include <err.h>
 #include <assert.h>
 #include <stdbool.h>
+#include <stddef.h>
 #include <stdio.h>
+#include <string.h>
 #include <strings.h>
 #include <vmmapi.h>
 #define	KASSERT(exp,msg)	assert((exp))
@@ -1990,22 +1992,36 @@ vie_calculate_gla(enum vm_cpu_mode cpu_mode, enum vm_r
 	return (0);
 }
 
+/*
+ * Prepare a partially decoded vie for a 2nd attempt.
+ */
 void
-vie_init(struct vie *vie, const char *inst_bytes, int inst_length)
+vie_restart(struct vie *vie)
 {
-	KASSERT(inst_length >= 0 && inst_length <= VIE_INST_SIZE,
-	    ("%s: invalid instruction length (%d)", __func__, inst_length));
+	_Static_assert(
+	    offsetof(struct vie, inst) < offsetof(struct vie, vie_startzero) &&
+	    offsetof(struct vie, num_valid) < offsetof(struct vie, vie_startzero),
+	    "restart should not erase instruction length or contents");
 
-	bzero(vie, sizeof(struct vie));
+	memset((char *)vie + offsetof(struct vie, vie_startzero), 0,
+	    sizeof(*vie) - offsetof(struct vie, vie_startzero));
 
 	vie->base_register = VM_REG_LAST;
 	vie->index_register = VM_REG_LAST;
 	vie->segment_register = VM_REG_LAST;
+}
 
-	if (inst_length) {
-		bcopy(inst_bytes, vie->inst, inst_length);
-		vie->num_valid = inst_length;
-	}
+void
+vie_init(struct vie *vie, const char *inst_bytes, int inst_length)
+{
+	KASSERT(inst_length >= 0 && inst_length <= VIE_INST_SIZE,
+	    ("%s: invalid instruction length (%d)", __func__, inst_length));
+
+	vie_restart(vie);
+	memset(vie->inst, 0, sizeof(vie->inst));
+	if (inst_length != 0)
+		memcpy(vie->inst, inst_bytes, inst_length);
+	vie->num_valid = inst_length;
 }
 
 #ifdef _KERNEL

Modified: head/usr.sbin/bhyve/bhyverun.c
==============================================================================
--- head/usr.sbin/bhyve/bhyverun.c	Thu Jun 25 00:09:43 2020	(r362599)
+++ head/usr.sbin/bhyve/bhyverun.c	Thu Jun 25 00:18:42 2020	(r362600)
@@ -80,6 +80,7 @@ __FBSDID("$FreeBSD$");
 #ifndef WITHOUT_CAPSICUM
 #include <machine/vmm_dev.h>
 #endif
+#include <machine/vmm_instruction_emul.h>
 #include <vmmapi.h>
 
 #include "bhyverun.h"
@@ -746,12 +747,26 @@ vmexit_mtrap(struct vmctx *ctx, struct vm_exit *vmexit
 static int
 vmexit_inst_emul(struct vmctx *ctx, struct vm_exit *vmexit, int *pvcpu)
 {
-	int err, i;
+	int err, i, cs_d;
 	struct vie *vie;
+	enum vm_cpu_mode mode;
 
 	stats.vmexit_inst_emul++;
 
 	vie = &vmexit->u.inst_emul.vie;
+	if (!vie->decoded) {
+		/*
+		 * Attempt to decode in userspace as a fallback.  This allows
+		 * updating instruction decode in bhyve without rebooting the
+		 * kernel (rapid prototyping), albeit with much slower
+		 * emulation.
+		 */
+		vie_restart(vie);
+		mode = vmexit->u.inst_emul.paging.cpu_mode;
+		cs_d = vmexit->u.inst_emul.cs_d;
+		(void)vmm_decode_instruction(mode, cs_d, vie);
+	}
+
 	err = emulate_mem(ctx, *pvcpu, vmexit->u.inst_emul.gpa,
 	    vie, &vmexit->u.inst_emul.paging);