window to the user stack while in a nested kernel trap. We do this for
entry to the kernel from user mode, but if we get an interrupt in kernel
mode while there are still user windows in the cpu, and we attempt to spill
to the user stack, we may take too many nested traps and overflow the trap
stack, causing a red state exception. This is needed by upcoming changes
to allow the user tsb to not be locked in the tlb.
Reviewed by: tmm
with user windows in kernel mode. We split the windows using %otherwin,
but instead of spilling user window directly to the pcb, we attempt to
spill to user space. If this fails because a stack page is not resident
(or the stack is smashed), the fault handler at tl 2 will detect the
situation and resume at tl 1 again where recovery code can spill to the
pcb. Any windows that have been saved to the pcb will be copied out to
the user stack on return from kernel mode.
Add a first stab at 32 bit window handling. This uses much of the same
recovery code as above because the alignment of the stack pointer is used
to detect 32 bit code. Attempting to spill a 32 bit window to a 64 bit
stack, or vice versa, will cause an alignment fault. The recovery code
then changes the window state to vector to a 32 bit spill/fill handler
and retries the faulting instruction.
Add ktr traces in useful places during trap processing.
Adjust comments to reflect new code and add many more.
