From: Kevin Brodsky <kevin.brodsky@arm.com> mainline inclusion from mainline-v6.19-rc2 commit b7737c38e7cb611c2fbd87af3b09afeb92c96fe7 category: feature bugzilla: https://atomgit.com/openeuler/kernel/issues/9850 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... ------------------------------------------- TL;DR: checking force_pte_mapping() in arch_kfence_init_pool() is sufficient Commit ce2b3a50ad92 ("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 53357f14f924 ("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: Kevin Brodsky <kevin.brodsky@arm.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com> --- arch/arm64/mm/mmu.c | 33 ++++++++++++++++----------------- 1 file changed, 16 insertions(+), 17 deletions(-) diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index 792ef9491280..405342e88cb3 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -663,18 +663,6 @@ 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) @@ -682,11 +670,22 @@ 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 (!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 (!split_leaf_mapping_possible() || is_kfence_address((void *)start)) + if (force_pte_mapping() || is_kfence_address((void *)start)) return 0; /* @@ -990,7 +989,7 @@ 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. */ -- 2.43.0