Driver::Submit checks the title's submission packet, which the title
passes on its own thread stack. Host thread stacks are neither registry
mappings nor write-watched, so no page-state cache covers them and on
Linux every check scans /proc/self/maps line by line: about 1.5 ms per
submission on the render thread of PPSA21564 (66% of that thread's
samples in perf at the title).
A range between the calling thread's current frame and its stack's top
holds the frames of every caller, so it is mapped readable and writable
for as long as the call lasts; verify() now accepts it without a query.
A thread on another stack (a fiber's, a signal stack) has its frame
outside the thread's bounds and still gets the page query, as does any
range that runs past the stack's top or starts below the frame.
GetCurrentThreadStackLimits needs _WIN32_WINNT 0x0602 on MinGW, as
libkernel already sets; GuestMemory.cpp is compiled by several targets,
so the definition is a property of the source file.
Dean Galvin