int
vmcb_setdesc(void *arg, int vcpu, int reg, struct seg_desc *desc)
{
struct vmcb *vmcb;
struct svm_softc *sc;
struct vmcb_segment *seg;
uint16_t attrib;
sc = arg;
vmcb = svm_get_vmcb(sc, vcpu);
seg = vmcb_segptr(vmcb, reg);
KASSERT(seg != NULL, ("%s: invalid segment descriptor %d",
__func__, reg));
seg->base = desc->base;
seg->limit = desc->limit;
if (reg != VM_REG_GUEST_GDTR && reg != VM_REG_GUEST_IDTR) {
/*
* Map seg_desc access to VMCB attribute format.
*
* SVM uses the 'P' bit in the segment attributes to indicate a
* NULL segment so clear it if the segment is marked unusable.
*/
attrib = ((desc->access & 0xF000) >> 4) | (desc->access & 0xFF);
if (SEG_DESC_UNUSABLE(desc->access)) {
attrib &= ~0x80;
}
seg->attrib = attrib;
}
/*
* Return 0 if the selector 'sel' in within the limits of the GDT/LDT
* and non-zero otherwise.
*/
static int
desc_table_limit_check(struct vmctx *ctx, int vcpu, uint16_t sel)
{
uint64_t base;
uint32_t limit, access;
int error, reg;
reg = ISLDT(sel) ? VM_REG_GUEST_LDTR : VM_REG_GUEST_GDTR;
error = vm_get_desc(ctx, vcpu, reg, &base, &limit, &access);
assert(error == 0);
if (reg == VM_REG_GUEST_LDTR) {
if (SEG_DESC_UNUSABLE(access) || !SEG_DESC_PRESENT(access))
return (-1);
}
if (limit < SEL_LIMIT(sel))
return (-1);
else
return (0);
}
int
vmexit_task_switch(struct vmctx *ctx, struct vm_exit *vmexit, int *pvcpu)
{
struct seg_desc nt;
struct tss32 oldtss, newtss;
struct vm_task_switch *task_switch;
struct vm_guest_paging *paging, sup_paging;
struct user_segment_descriptor nt_desc, ot_desc;
struct iovec nt_iov[2], ot_iov[2];
uint64_t cr0, ot_base;
uint32_t eip, ot_lim, access;
int error, ext, minlimit, nt_type, ot_type, vcpu;
enum task_switch_reason reason;
uint16_t nt_sel, ot_sel;
task_switch = &vmexit->u.task_switch;
nt_sel = task_switch->tsssel;
ext = vmexit->u.task_switch.ext;
reason = vmexit->u.task_switch.reason;
paging = &vmexit->u.task_switch.paging;
vcpu = *pvcpu;
assert(paging->cpu_mode == CPU_MODE_PROTECTED);
/*
* Section 4.6, "Access Rights" in Intel SDM Vol 3.
* The following page table accesses are implicitly supervisor mode:
* - accesses to GDT or LDT to load segment descriptors
* - accesses to the task state segment during task switch
*/
sup_paging = *paging;
sup_paging.cpl = 0; /* implicit supervisor mode */
/* Fetch the new TSS descriptor */
error = read_tss_descriptor(ctx, vcpu, task_switch, nt_sel, &nt_desc);
CHKERR(error);
nt = usd_to_seg_desc(&nt_desc);
/* Verify the type of the new TSS */
nt_type = SEG_DESC_TYPE(nt.access);
if (nt_type != SDT_SYS386BSY && nt_type != SDT_SYS386TSS &&
nt_type != SDT_SYS286BSY && nt_type != SDT_SYS286TSS) {
sel_exception(ctx, vcpu, IDT_TS, nt_sel, ext);
goto done;
}
/* TSS descriptor must have present bit set */
if (!SEG_DESC_PRESENT(nt.access)) {
sel_exception(ctx, vcpu, IDT_NP, nt_sel, ext);
goto done;
}
/*
* TSS must have a minimum length of 104 bytes for a 32-bit TSS and
* 44 bytes for a 16-bit TSS.
*/
if (nt_type == SDT_SYS386BSY || nt_type == SDT_SYS386TSS)
minlimit = 104 - 1;
else if (nt_type == SDT_SYS286BSY || nt_type == SDT_SYS286TSS)
minlimit = 44 - 1;
else
minlimit = 0;
assert(minlimit > 0);
if (nt.limit < minlimit) {
sel_exception(ctx, vcpu, IDT_TS, nt_sel, ext);
goto done;
}
/* TSS must be busy if task switch is due to IRET */
if (reason == TSR_IRET && !TSS_BUSY(nt_type)) {
sel_exception(ctx, vcpu, IDT_TS, nt_sel, ext);
goto done;
}
/*
* TSS must be available (not busy) if task switch reason is
* CALL, JMP, exception or interrupt.
*/
if (reason != TSR_IRET && TSS_BUSY(nt_type)) {
sel_exception(ctx, vcpu, IDT_GP, nt_sel, ext);
goto done;
}
/* Fetch the new TSS */
error = vm_copy_setup(ctx, vcpu, &sup_paging, nt.base, minlimit + 1,
PROT_READ | PROT_WRITE, nt_iov, nitems(nt_iov));
CHKERR(error);
vm_copyin(ctx, vcpu, nt_iov, &newtss, minlimit + 1);
/* Get the old TSS selector from the guest's task register */
ot_sel = GETREG(ctx, vcpu, VM_REG_GUEST_TR);
if (ISLDT(ot_sel) || IDXSEL(ot_sel) == 0) {
/*
* This might happen if a task switch was attempted without
* ever loading the task register with LTR. In this case the
* TR would contain the values from power-on:
* (sel = 0, base = 0, limit = 0xffff).
*/
sel_exception(ctx, vcpu, IDT_TS, ot_sel, task_switch->ext);
goto done;
}
/* Get the old TSS base and limit from the guest's task register */
error = vm_get_desc(ctx, vcpu, VM_REG_GUEST_TR, &ot_base, &ot_lim,
&access);
assert(error == 0);
assert(!SEG_DESC_UNUSABLE(access) && SEG_DESC_PRESENT(access));
ot_type = SEG_DESC_TYPE(access);
assert(ot_type == SDT_SYS386BSY || ot_type == SDT_SYS286BSY);
/* Fetch the old TSS descriptor */
error = read_tss_descriptor(ctx, vcpu, task_switch, ot_sel, &ot_desc);
CHKERR(error);
/* Get the old TSS */
error = vm_copy_setup(ctx, vcpu, &sup_paging, ot_base, minlimit + 1,
PROT_READ | PROT_WRITE, ot_iov, nitems(ot_iov));
CHKERR(error);
vm_copyin(ctx, vcpu, ot_iov, &oldtss, minlimit + 1);
/*
* Clear the busy bit in the old TSS descriptor if the task switch
* due to an IRET or JMP instruction.
*/
if (reason == TSR_IRET || reason == TSR_JMP) {
ot_desc.sd_type &= ~0x2;
error = desc_table_write(ctx, vcpu, &sup_paging, ot_sel,
&ot_desc);
CHKERR(error);
}
if (nt_type == SDT_SYS286BSY || nt_type == SDT_SYS286TSS) {
fprintf(stderr, "Task switch to 16-bit TSS not supported\n");
return (VMEXIT_ABORT);
}
/* Save processor state in old TSS */
eip = vmexit->rip + vmexit->inst_length;
tss32_save(ctx, vcpu, task_switch, eip, &oldtss, ot_iov);
/*
* If the task switch was triggered for any reason other than IRET
* then set the busy bit in the new TSS descriptor.
*/
if (reason != TSR_IRET) {
nt_desc.sd_type |= 0x2;
error = desc_table_write(ctx, vcpu, &sup_paging, nt_sel,
&nt_desc);
CHKERR(error);
}
/* Update task register to point at the new TSS */
SETREG(ctx, vcpu, VM_REG_GUEST_TR, nt_sel);
/* Update the hidden descriptor state of the task register */
nt = usd_to_seg_desc(&nt_desc);
update_seg_desc(ctx, vcpu, VM_REG_GUEST_TR, &nt);
/* Set CR0.TS */
cr0 = GETREG(ctx, vcpu, VM_REG_GUEST_CR0);
SETREG(ctx, vcpu, VM_REG_GUEST_CR0, cr0 | CR0_TS);
/*
* We are now committed to the task switch. Any exceptions encountered
* after this point will be handled in the context of the new task and
* the saved instruction pointer will belong to the new task.
*/
vmexit->rip = newtss.tss_eip;
vmexit->inst_length = 0;
/* Load processor state from new TSS */
error = tss32_restore(ctx, vcpu, task_switch, ot_sel, &newtss, nt_iov);
CHKERR(error);
/*
* Section "Interrupt Tasks" in Intel SDM, Vol 3: if an exception
* caused an error code to be generated, this error code is copied
* to the stack of the new task.
*/
if (task_switch->errcode_valid) {
assert(task_switch->ext);
assert(task_switch->reason == TSR_IDT_GATE);
error = push_errcode(ctx, vcpu, &task_switch->paging, nt_type,
task_switch->errcode);
CHKERR(error);
}
/*
* Treatment of virtual-NMI blocking if NMI is delivered through
* a task gate.
*
* Section "Architectural State Before A VM Exit", Intel SDM, Vol3:
* If the virtual NMIs VM-execution control is 1, VM entry injects
* an NMI, and delivery of the NMI causes a task switch that causes
* a VM exit, virtual-NMI blocking is in effect before the VM exit
* commences.
*
* Thus, virtual-NMI blocking is in effect at the time of the task
* switch VM exit.
*/
/*
* Treatment of virtual-NMI unblocking on IRET from NMI handler task.
*
* Section "Changes to Instruction Behavior in VMX Non-Root Operation"
* If "virtual NMIs" control is 1 IRET removes any virtual-NMI blocking.
* This unblocking of virtual-NMI occurs even if IRET causes a fault.
*
* Thus, virtual-NMI blocking is cleared at the time of the task switch
* VM exit.
*/
/*
* If the task switch was triggered by an event delivered through
* the IDT then extinguish the pending event from the vcpu's
* exitintinfo.
*/
if (task_switch->reason == TSR_IDT_GATE) {
error = vm_set_intinfo(ctx, vcpu, 0);
assert(error == 0);
}
/*
* XXX should inject debug exception if 'T' bit is 1
*/
done:
return (VMEXIT_CONTINUE);
}
