arm64: mm: Don't sleep in split_kernel_leaf_mapping() when in atomic context

It has been reported that split_kernel_leaf_mapping() is trying to sleep
in non-sleepable context. It does this when acquiring the
pgtable_split_lock mutex, when either CONFIG_DEBUG_PAGEALLOC or
CONFIG_KFENCE are enabled, which change linear map permissions within
softirq context during memory allocation and/or freeing. All other paths
into this function are called from sleepable context and so are safe.

But it turns out that the memory for which these 2 features may attempt
to modify the permissions is always mapped by pte, so there is no need
to attempt to split the mapping. So let's exit early in these cases and
avoid attempting to take the mutex.

There is one wrinkle to this approach; late-initialized kfence allocates
it's pool from the buddy which may be block mapped. So we must hook that
allocation and convert it to pte-mappings up front. Previously this was
done as a side-effect of kfence protecting all the individual pages in
its pool at init-time, but this no longer works due to the added early
exit path in split_kernel_leaf_mapping().

So instead, do this via the existing arch_kfence_init_pool() arch hook,
and reuse the existing linear_map_split_to_ptes() infrastructure.

Closes: https://lore.kernel.org/all/f24b9032-0ec9-47b1-8b95-c0eeac7a31c5@roeck-us.net/
Fixes: a166563e7ec3 ("arm64: mm: support large block mapping when rodata=full")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <groeck@google.com>
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: David Hildenbrand (Red Hat) <david@kernel.org>
Reviewed-by: Yang Shi <yang@os.amperecomputing.com>
Signed-off-by: Will Deacon <will@kernel.org>

0 files changed, 0 insertions, 0 deletions