arm64: mm: Make kaslr_requires_kpti() a static inline

In preparation for moving the first assignment of arm64_use_ng_mappings
to an earlier stage in the boot, ensure that kaslr_requires_kpti() is
accessible without relying on the core kernel's view on whether or not
KASLR is enabled. So make it a static inline, and move the
kaslr_enabled() check out of it and into the callers, one of which will
disappear in a subsequent patch.

Once/when support for the obsolete ThunderX 1 platform is dropped, this
check reduces to a E0PD feature check on the local CPU.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20240214122845.2033971-61-ardb+git@google.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 37 insertions, 1 deletions

diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
index 2fcf51231d6e..d0b8b4b413b6 100644
--- a/arch/arm64/include/asm/mmu.h
+++ b/arch/arm64/include/asm/mmu.h
@@ -71,7 +71,43 @@ extern void create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
 			       pgprot_t prot, bool page_mappings_only);
 extern void *fixmap_remap_fdt(phys_addr_t dt_phys, int *size, pgprot_t prot);
 extern void mark_linear_text_alias_ro(void);
-extern bool kaslr_requires_kpti(void);
+
+/*
+ * This check is triggered during the early boot before the cpufeature
+ * is initialised. Checking the status on the local CPU allows the boot
+ * CPU to detect the need for non-global mappings and thus avoiding a
+ * pagetable re-write after all the CPUs are booted. This check will be
+ * anyway run on individual CPUs, allowing us to get the consistent
+ * state once the SMP CPUs are up and thus make the switch to non-global
+ * mappings if required.
+ */
+static inline bool kaslr_requires_kpti(void)
+{
+	/*
+	 * E0PD does a similar job to KPTI so can be used instead
+	 * where available.
+	 */
+	if (IS_ENABLED(CONFIG_ARM64_E0PD)) {
+		u64 mmfr2 = read_sysreg_s(SYS_ID_AA64MMFR2_EL1);
+		if (cpuid_feature_extract_unsigned_field(mmfr2,
+						ID_AA64MMFR2_EL1_E0PD_SHIFT))
+			return false;
+	}
+
+	/*
+	 * Systems affected by Cavium erratum 24756 are incompatible
+	 * with KPTI.
+	 */
+	if (IS_ENABLED(CONFIG_CAVIUM_ERRATUM_27456)) {
+		extern const struct midr_range cavium_erratum_27456_cpus[];
+
+		if (is_midr_in_range_list(read_cpuid_id(),
+					  cavium_erratum_27456_cpus))
+			return false;
+	}
+
+	return true;
+}
 
 #define INIT_MM_CONTEXT(name)	\
 	.pgd = init_pg_dir,