Remove the protection against huge vmap permission adjustments on systems that support the bbml2_no_abort CPU feature. Splitting live kernel VA section mappings into page mappings was restricted because it could cause TLB Conflict Aborts. This forced permission adjustments on memory allocated with VM_ALLOW_HUGE_VMAP to be rejected, resulting in performance drops (e.g., when enforcing rodata=on disables huge mappings). The bbml2_no_abort feature (which mirrors the architectural guarantees of FEAT_BBML3) ensures that changing between table and block sizes without following a break-before-make sequence will not generate a TLB Conflict Abort. This hardware guarantee makes it safe to allow dynamic permission adjustments on huge vmap regions. Signed-off-by: Adrian Barnaś --- arch/arm64/mm/pageattr.c | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-) diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c index 358d1dc9a576..88720bbba892 100644 --- a/arch/arm64/mm/pageattr.c +++ b/arch/arm64/mm/pageattr.c @@ -157,23 +157,29 @@ static int change_memory_common(unsigned long addr, int numpages, } /* - * Kernel VA mappings are always live, and splitting live section - * mappings into page mappings may cause TLB conflicts. This means - * we have to ensure that changing the permission bits of the range - * we are operating on does not result in such splitting. - * * Let's restrict ourselves to mappings created by vmalloc (or vmap). - * Disallow VM_ALLOW_HUGE_VMAP mappings to guarantee that only page - * mappings are updated and splitting is never needed. * * So check whether the [addr, addr + size) interval is entirely * covered by precisely one VM area that has the VM_ALLOC flag set. */ area = find_vm_area((void *)addr); + if (!area || ((unsigned long)kasan_reset_tag((void *)end) > (unsigned long)kasan_reset_tag(area->addr) + area->size) || - ((area->flags & (VM_ALLOC | VM_ALLOW_HUGE_VMAP)) != VM_ALLOC)) + !(area->flags & VM_ALLOC)) + return -EINVAL; + + /* + * Kernel VA mappings are always live, and splitting live section + * mappings into page mappings may cause TLB conflicts if bbml2_noabort + * is not present. + * + * While bbml2_noabort is not present disallow VM_ALLOW_HUGE_VMAP mappings + * to guarantee that only page mappings are updated and splitting is not + * needed. + */ + if (!system_supports_bbml2_noabort() && (area->flags & (VM_ALLOW_HUGE_VMAP))) return -EINVAL; if (!numpages) -- 2.54.0.1136.gdb2ca164c4-goog