On Wed, Oct 16, 2024 at 03:24:23PM +0300, Mike Rapoport wrote:

From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>

Using large pages to map text areas reduces iTLB pressure and improves
performance.

Extend execmem_alloc() with an ability to use huge pages with ROX
permissions as a cache for smaller allocations.

To populate the cache, a writable large page is allocated from vmalloc with
VM_ALLOW_HUGE_VMAP, filled with invalid instructions and then remapped as
ROX.

The direct map alias of that large page is exculded from the direct map.

Portions of that large page are handed out to execmem_alloc() callers
without any changes to the permissions.

When the memory is freed with execmem_free() it is invalidated again so
that it won't contain stale instructions.

An architecture has to implement execmem_fill_trapping_insns() callback
and select ARCH_HAS_EXECMEM_ROX configuration option to be able to use
the ROX cache.

The cache is enabled on per-range basis when an architecture sets
EXECMEM_ROX_CACHE flag in definition of an execmem_range.

Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>

  Luis