@@ -38,10 +38,21 @@ static inline bool arm64_kernel_unmapped_at_el0(void)
static inline bool kaslr_requires_kpti(void)
{
bool tx1_bug;
+ u64 ftr;
if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE))
return false;
+ /*
+ * E0PD does a similar job to KPTI so can be used instead
+ * where available.
+ */
+ if (IS_ENABLED(CONFIG_ARM64_E0PD)) {
+ ftr = read_sysreg_s(SYS_ID_AA64MMFR2_EL1);
+ if ((ftr >> ID_AA64MMFR2_E0PD_SHIFT) & 0xf)
+ return false;
+ }
+
/*
* Systems affected by Cavium erratum 24756 are incompatible
* with KPTI.
Since E0PD is intended to fulfil the same role as KPTI we don't need to use KPTI on CPUs where E0PD is available, we can rely on E0PD instead. Change the check that forces KPTI on when KASLR is enabled to check for E0PD before doing so, CPUs with E0PD are not expected to be affected by meltdown so should not need to enable KPTI for other reasons. Since E0PD is a system capability we will still enable KPTI if any of the CPUs in the system lacks E0PD, this will rewrite any global mappings that were established in systems where some but not all CPUs support E0PD. We may transiently have a mix of global and non-global mappings while booting since we use the local CPU when deciding if KPTI will be required prior to completing CPU enumeration but any global mappings will be converted to non-global ones when KPTI is applied. KPTI can still be forced on from the command line if required. Signed-off-by: Mark Brown <broonie@kernel.org> --- arch/arm64/include/asm/mmu.h | 11 +++++++++++ 1 file changed, 11 insertions(+)