On Thu, Jan 25, 2024 at 8:43 AM Alexandru Elisei
[off-list ref] wrote:

arm64 uses VM_HIGH_ARCH_0 and VM_HIGH_ARCH_1 for enabling MTE for a VMA.
When VM_HIGH_ARCH_0, which arm64 renames to VM_MTE, is set for a VMA, and
the gfp flag __GFP_ZERO is present, the __GFP_ZEROTAGS gfp flag also gets
set in vma_alloc_zeroed_movable_folio().

Expand this to be more generic by adding an arch hook that modifes the gfp
flags for an allocation when the VMA is known.

Note that __GFP_ZEROTAGS is ignored by the page allocator unless __GFP_ZERO
is also set; from that point of view, the current behaviour is unchanged,
even though the arm64 flag is set in more places.  When arm64 will have
support to reuse the tag storage for data allocation, the uses of the
__GFP_ZEROTAGS flag will be expanded to instruct the page allocator to try
to reserve the corresponding tag storage for the pages being allocated.

The flags returned by arch_calc_vma_gfp() are or'ed with the flags set by
the caller; this has been done to keep an architecture from modifying the
flags already set by the core memory management code; this is similar to
how do_mmap() -> calc_vm_flag_bits() -> arch_calc_vm_flag_bits() has been
implemented. This can be revisited in the future if there's a need to do
so.

Signed-off-by: Alexandru Elisei <redacted>

This patch also needs to update the non-CONFIG_NUMA definition of
vma_alloc_folio in include/linux/gfp.h to call arch_calc_vma_gfp. See:
https://r.android.com/2849146

Peter