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bhyve: refactor gdbstub to enable single-stepping on AMD CPUs

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This patch refactors the existing Intel-specific single-stepping
mechanism in bhyve's GDB stub to work with both AMD and Intel CPUs.

Reviewed by:	jhb
Sponsored by:	Google, Inc. (GSoC 2022)
Differential Revision: https://reviews.freebsd.org/D42298
This commit is contained in:
Bojan Novković 2023-12-12 15:28:59 -08:00 committed by John Baldwin
parent 5c7a909271
commit ca96a942ca
3 changed files with 93 additions and 17 deletions
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15
usr.sbin/bhyve/amd64/vmexit.c
View file

@ -439,6 +439,20 @@ vmexit_debug(struct vmctx *ctx __unused, struct vcpu *vcpu,
return (VMEXIT_CONTINUE);
}
static int
vmexit_db(struct vmctx *ctx __unused, struct vcpu *vcpu, struct vm_run *vmrun)
{
#ifdef BHYVE_SNAPSHOT
checkpoint_cpu_suspend(vcpu_id(vcpu));
#endif
gdb_cpu_debug(vcpu, vmrun->vm_exit);
#ifdef BHYVE_SNAPSHOT
checkpoint_cpu_resume(vcpu_id(vcpu));
#endif
return (VMEXIT_CONTINUE);
}
static int
vmexit_breakpoint(struct vmctx *ctx __unused, struct vcpu *vcpu,
struct vm_run *vmrun)
@ -503,4 +517,5 @@ const vmexit_handler_t vmexit_handlers[VM_EXITCODE_MAX] = {
[VM_EXITCODE_IPI] = vmexit_ipi,
[VM_EXITCODE_HLT] = vmexit_hlt,
[VM_EXITCODE_PAUSE] = vmexit_pause,
[VM_EXITCODE_DB] = vmexit_db,
};

94
usr.sbin/bhyve/gdb.c
View file

@ -743,6 +743,43 @@ _gdb_cpu_suspend(struct vcpu *vcpu, bool report_stop)
debug("$vCPU %d resuming\n", vcpuid);
}
/*
* Requests vCPU single-stepping using a
* VMEXIT suitable for the host platform.
*/
static int
_gdb_set_step(struct vcpu *vcpu, int val)
{
int error;
/*
* If the MTRAP cap fails, we are running on an AMD host.
* In that case, we request DB exits caused by RFLAGS.TF.
*/
error = vm_set_capability(vcpu, VM_CAP_MTRAP_EXIT, val);
if (error != 0)
error = vm_set_capability(vcpu, VM_CAP_RFLAGS_TF, val);
if (error == 0)
(void)vm_set_capability(vcpu, VM_CAP_MASK_HWINTR, val);
return (error);
}
/*
* Checks whether single-stepping is enabled for a given vCPU.
*/
static int
_gdb_check_step(struct vcpu *vcpu)
{
int val;
if (vm_get_capability(vcpu, VM_CAP_MTRAP_EXIT, &val) != 0) {
if (vm_get_capability(vcpu, VM_CAP_RFLAGS_TF, &val) != 0)
return -1;
}
return 0;
}
/*
* Invoked at the start of a vCPU thread's execution to inform the
* debug server about the new thread.
@ -797,10 +834,7 @@ gdb_cpu_resume(struct vcpu *vcpu)
assert(vs->hit_swbreak == false);
assert(vs->stepped == false);
if (vs->stepping) {
error = vm_set_capability(vcpu, VM_CAP_MTRAP_EXIT, 1);
assert(error == 0);
error = vm_set_capability(vcpu, VM_CAP_MASK_HWINTR, 1);
error = _gdb_set_step(vcpu, 1);
assert(error == 0);
}
}
@ -835,26 +869,24 @@ gdb_suspend_vcpus(void)
}
/*
* Handler for VM_EXITCODE_MTRAP reported when a vCPU single-steps via
* the VT-x-specific MTRAP exit.
* Invoked each time a vmexit handler needs to step a vCPU.
* Handles MTRAP and RFLAGS.TF vmexits.
*/
void
gdb_cpu_mtrap(struct vcpu *vcpu)
static void
gdb_cpu_step(struct vcpu *vcpu)
{
struct vcpu_state *vs;
int vcpuid;
int vcpuid = vcpu_id(vcpu);
int error;
if (!gdb_active)
return;
vcpuid = vcpu_id(vcpu);
debug("$vCPU %d MTRAP\n", vcpuid);
debug("$vCPU %d stepped\n", vcpuid);
pthread_mutex_lock(&gdb_lock);
vs = &vcpu_state[vcpuid];
if (vs->stepping) {
vs->stepping = false;
vs->stepped = true;
vm_set_capability(vcpu, VM_CAP_MTRAP_EXIT, 0);
vm_set_capability(vcpu, VM_CAP_MASK_HWINTR, 0);
error = _gdb_set_step(vcpu, 0);
assert(error == 0);
while (vs->stepped) {
if (stopped_vcpu == -1) {
@ -869,6 +901,34 @@ gdb_cpu_mtrap(struct vcpu *vcpu)
pthread_mutex_unlock(&gdb_lock);
}
/*
* A general handler for VM_EXITCODE_DB.
* Handles RFLAGS.TF exits on AMD SVM.
*/
void
gdb_cpu_debug(struct vcpu *vcpu, struct vm_exit *vmexit)
{
if (!gdb_active)
return;
/* RFLAGS.TF exit? */
if (vmexit->u.dbg.trace_trap) {
gdb_cpu_step(vcpu);
}
}
/*
* Handler for VM_EXITCODE_MTRAP reported when a vCPU single-steps via
* the VT-x-specific MTRAP exit.
*/
void
gdb_cpu_mtrap(struct vcpu *vcpu)
{
if (!gdb_active)
return;
gdb_cpu_step(vcpu);
}
static struct breakpoint *
find_breakpoint(uint64_t gpa)
{
@ -940,11 +1000,11 @@ gdb_cpu_breakpoint(struct vcpu *vcpu, struct vm_exit *vmexit)
static bool
gdb_step_vcpu(struct vcpu *vcpu)
{
int error, val, vcpuid;
int error, vcpuid;
vcpuid = vcpu_id(vcpu);
debug("$vCPU %d step\n", vcpuid);
error = vm_get_capability(vcpu, VM_CAP_MTRAP_EXIT, &val);
error = _gdb_check_step(vcpu);
if (error < 0)
return (false);

1
usr.sbin/bhyve/gdb.h
View file

@ -32,6 +32,7 @@ void gdb_cpu_add(struct vcpu *vcpu);
void gdb_cpu_breakpoint(struct vcpu *vcpu, struct vm_exit *vmexit);
void gdb_cpu_mtrap(struct vcpu *vcpu);
void gdb_cpu_suspend(struct vcpu *vcpu);
void gdb_cpu_debug(struct vcpu *vcpu, struct vm_exit *vmexit);
void init_gdb(struct vmctx *ctx);
#endif /* !__GDB_H__ */