/**
* \brief Switch context to 'dcb'.
*
* Switch to the dispatcher pointed to by 'dcb'. Sets 'dcb_current'.
*
* \param dcb Pointer to dispatcher to which to switch context.
*/
void
context_switch(struct dcb *dcb) {
struct dispatcher_shared_generic *disp =
get_dispatcher_shared_generic(dcb->disp);
assert(dcb != NULL);
assert(dcb->vspace != 0);
// VM guests do not have a user space dispatcher
if (!dcb->is_vm_guest) {
assert(dcb->disp != 0);
}
paging_context_switch(dcb->vspace);
context_switch_counter++;
/* Write the CONTEXTID register, so that the debugger can tell dispatchers
* apart. We use the physical address of the dispatcher control block.
* Note that the low 10 bits of dcb are zero, and the lower 8 bits of the
* register hold the ASID, which we're not yet using. */
cp15_write_contextidr(((uint32_t)dcb) & ~MASK(8));
if (!dcb->is_vm_guest) {
assert(dcb->disp_cte.cap.type == ObjType_Frame);
/*
* The name of the function is somewhat misleading. we need an unused
* user register that always stores the pointer to the current
* dispatcher. most ABIs define a register for thread-local storage,
* and we have been abusing that on x64 for the dispatcher pointer
* --arch_set_thread_ register sets this pointer. Obviously this
* needs to change to support thread-local storage using a standard
* ABI, so we will have to figure out how to get to the dispatcher
* from something like a thread-local variable. The reason that this
* is in the switch path and not in resume/execute is that on x86_64
* loading the thread register (fs) is stupidly expensive, so we avoid
* doing it unless we switch contexts -- presumably that could be a
* local optimisation in the x86_64 dispatch paths rather than the
* generic context_switch path/
*/
arch_set_thread_register(disp->udisp);
}
}
/**
* \brief Switch context to 'dcb'.
*
* Switch to the dispatcher pointed to by 'dcb'. Sets 'dcb_current'.
*
* \param dcb Pointer to dispatcher to which to switch context.
*/
void
context_switch(struct dcb *dcb) {
struct dispatcher_shared_generic *disp =
get_dispatcher_shared_generic(dcb->disp);
assert(dcb != NULL);
assert(dcb->vspace != 0);
// VM guests do not have a user space dispatcher
if (!dcb->is_vm_guest) {
assert(dcb->disp != 0);
}
paging_context_switch(dcb->vspace);
context_switch_counter++;
if (!dcb->is_vm_guest) {
assert(dcb->disp_cte.cap.type == ObjType_Frame);
/*
* The name of the function is somewhat misleading. we need an unused
* user register that always stores the pointer to the current
* dispatcher. most ABIs define a register for thread-local storage,
* and we have been abusing that on x64 for the dispatcher pointer
* --arch_set_thread_ register sets this pointer. Obviously this
* needs to change to support thread-local storage using a standard
* ABI, so we will have to figure out how to get to the dispatcher
* from something like a thread-local variable. The reason that this
* is in the switch path and not in resume/execute is that on x86_64
* loading the thread register (fs) is stupidly expensive, so we avoid
* doing it unless we switch contexts -- presumably that could be a
* local optimisation in the x86_64 dispatch paths rather than the
* generic context_switch path/
*/
arch_set_thread_register(disp->udisp);
}
}
