This fixes file descriptor leaks. Suppose relibc is just about to set
the address space. For this, it needs to write the address space fd to
the selection fd. To avoid having to close them in the kernel, it rather
memorizes what the file descriptors refer to internally, and then do the
actual operation when they are gone, i.e. when closing.
Turns out the problem all along was that the ActivePageTable was never
dropped in usermode_bootstrap. So as soon as any other hardware thread
tried to do page table business, it deadlocked!
This is so that any process can use pointers to ACPI tables, since they
now point to the universally-accessible KERNEL_OFFSET+physaddr virtual
addresses.
Currently, this uses a relatively naive method of simply scanning the
512 entries for the PRESENT flag. But, unless the optimizer cannot, it
can be reduced to calculating the bitwise OR of every entry and then
checking that.
If this turns out to be too slow, which it might be when unmapping lots
of pages, then we can (1) either fall back to using a counter like the
old paging code did, or even better (2) use the now-1:1 grants tree to
check if it became empty. Putting the grants code in RMM might be
suboptimal, so instead we can add "unmap_range" and have the kernel
paging code take the offset of the next grant, if any, and then possibly
unmap entire P1s/P2s/P3s -- whatever is in the page tables within that
range.
Note that I am fairly certain that method (1) was the cause of the
visually notorious orbital memory corruption bug.
4lDO2