Allowing iounmap() on memory that was not ioremap()'d in the first
place is obviously a bad idea.  There is currently a feeble attempt to
avoid errant iounmap()s by checking to see if the address is below
"high_memory".  But that's imprecise at best because there are plenty
of high addresses that are also invalid to call iounmap() on.

Thankfully, there is a more precise helper: is_ioremap_addr().  x86
just does not use it in iounmap().

Restrict iounmap() to addresses in the ioremap region, by using
is_ioremap_addr(). This aligns x86 closer to the generic iounmap()
implementation.

Additionally, add a warning in case there is an attempt to iounmap()
invalid memory.  This replaces an existing silent return and will
help alert folks to any incorrect usage of iounmap().

Due to VMALLOC_START on i386 not being present in asm/pgtable.h,
include for asm/vmalloc.h had to be added to include/linux/ioremap.h.

[ dhansen: tweak subject and changelog ]
Signed-off-by: Max Ramanouski <max8rr8@gmail.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Link: https://lore.kernel.org/all/20240824220111.84441-1-max8rr8%40gmail.com