Commit b7737c38 authored by Kevin Brodsky's avatar Kevin Brodsky Committed by Catalin Marinas
Browse files

arm64: mm: Simplify check in arch_kfence_init_pool() 



TL;DR: checking force_pte_mapping() in arch_kfence_init_pool() is
sufficient

Commit ce2b3a50 ("arm64: mm: Don't sleep in
split_kernel_leaf_mapping() when in atomic context") recently added
an arm64 implementation of arch_kfence_init_pool() to ensure that
the KFENCE pool is PTE-mapped. Assuming that the pool was not
initialised early, block splitting is necessary if the linear
mapping is not fully PTE-mapped, in other words if
force_pte_mapping() is false.

arch_kfence_init_pool() currently makes another check: whether
BBML2-noabort is supported, i.e. whether we are *able* to split
block mappings. This check is however unnecessary, because
force_pte_mapping() is always true if KFENCE is enabled and
BBML2-noabort is not supported. This must be the case by design,
since KFENCE requires PTE-mapped pages in all cases. We can
therefore remove that check.

The situation is different in split_kernel_leaf_mapping(), as that
function is called unconditionally regardless of the configuration.
If BBML2-noabort is not supported, it cannot do anything and bails
out. If force_pte_mapping() is true, there is nothing to do and it
also bails out, but these are independent checks.

Commit 53357f14 ("arm64: mm: Tidy up force_pte_mapping()")
grouped these checks into a helper, split_leaf_mapping_possible().
This isn't so helpful as only split_kernel_leaf_mapping() should
check both. Revert the parts of that commit that introduced the
helper, reintroducing the more accurate comments in
split_kernel_leaf_mapping().

Signed-off-by: default avatarKevin Brodsky <kevin.brodsky@arm.com>
Reviewed-by: default avatarRyan Roberts <ryan.roberts@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 8f0b4cce

arch/arm64/mm/mmu.c

+16 −17
Original line number Diff line number Diff line
@@ -767,18 +767,6 @@ static inline bool force_pte_mapping(void) 
	return rodata_full || arm64_kfence_can_set_direct_map() || is_realm_world();

}



static inline bool split_leaf_mapping_possible(void)

{

	/*

	 * !BBML2_NOABORT systems should never run into scenarios where we would

	 * have to split. So exit early and let calling code detect it and raise

	 * a warning.

	 */

	if (!system_supports_bbml2_noabort())

		return false;

	return !force_pte_mapping();

}



static DEFINE_MUTEX(pgtable_split_lock);



int split_kernel_leaf_mapping(unsigned long start, unsigned long end)
@@ -786,11 +774,22 @@ int split_kernel_leaf_mapping(unsigned long start, unsigned long end) 
	int ret;



	/*

	 * Exit early if the region is within a pte-mapped area or if we can't

	 * split. For the latter case, the permission change code will raise a

	 * warning if not already pte-mapped.

	 * !BBML2_NOABORT systems should not be trying to change permissions on

	 * anything that is not pte-mapped in the first place. Just return early

	 * and let the permission change code raise a warning if not already

	 * pte-mapped.

	 */

	if (!split_leaf_mapping_possible() || is_kfence_address((void *)start))

	if (!system_supports_bbml2_noabort())

		return 0;



	/*

	 * If the region is within a pte-mapped area, there is no need to try to

	 * split. Additionally, CONFIG_DEBUG_PAGEALLOC and CONFIG_KFENCE may

	 * change permissions from atomic context so for those cases (which are

	 * always pte-mapped), we must not go any further because taking the

	 * mutex below may sleep.

	 */

	if (force_pte_mapping() || is_kfence_address((void *)start))

		return 0;



	/*
@@ -1089,7 +1088,7 @@ bool arch_kfence_init_pool(void) 
	int ret;



	/* Exit early if we know the linear map is already pte-mapped. */

	if (!split_leaf_mapping_possible())

	if (force_pte_mapping())

		return true;



	/* Kfence pool is already pte-mapped for the early init case. */