mm/vmalloc: warn on invalid vmalloc gfp flags

mm/vmalloc: warn on invalid vmalloc gfp flags

Patch series "make vmalloc gfp flags usage more apparent", v4.

We should do a better job at enforcing gfp flags for vmalloc.  Right now,
we have a kernel-doc for __vmalloc_node_range(), and hope callers pass in
supported flags.  If a caller were to pass in an unsupported flag, we may
BUG, silently clear it, or completely ignore it.

If we are more proactive about enforcing gfp flags, we can making sure
callers know when they may be asking for unsupported behavior.

This patchset lets vmalloc control the incoming gfp flags, and cleans up
some hard to read gfp code.

This patch (of 4):

Vmalloc explicitly supports a list of flags, but we never enforce them.
vmalloc has been trying to handle unsupported flags by clearing and
setting flags wherever necessary.  This is messy and makes the code harder
to understand, when we could simply check for a supported input
immediately instead.

Define a helper mask and function telling callers they have passed in
invalid flags, and clear those unsupported vmalloc flags.

Link: https://lkml.kernel.org/r/20251121094405.40628-1-vishal.moola@gmail.com
Link: https://lkml.kernel.org/r/20251121094405.40628-2-vishal.moola@gmail.com
Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
Acked-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>