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bhyve(8): For prototyping, reattempt decode in userspace

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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
This commit is contained in:
Conrad Meyer 2020-06-25 00:18:42 +00:00
parent 54cca285fc
commit 4daa95f85d
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=362600
4 changed files with 46 additions and 11 deletions
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3
sys/amd64/include/vmm.h
View File

@ -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 */

1
sys/amd64/include/vmm_instruction_emul.h
View File

@ -105,6 +105,7 @@ int vm_gla2gpa_nofault(struct vm *vm, int vcpuid, struct vm_guest_paging *paging
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);
/*

36
sys/amd64/vmm/vmm_instruction_emul.c
View File

@ -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_reg_name seg,
return (0);
}
/*
* Prepare a partially decoded vie for a 2nd attempt.
*/
void
vie_restart(struct vie *vie)
{
_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");
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;
}
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));
bzero(vie, sizeof(struct vie));
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;
}
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

17
usr.sbin/bhyve/bhyverun.c
View File

@ -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, int *pvcpu)
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);