arm64: Treat HCR_EL2.E2H as RES1 when ID_AA64MMFR4_EL1.E2H0 is negative

For CPUs that have ID_AA64MMFR4_EL1.E2H0 as negative, it is important
to avoid the boot path that sets HCR_EL2.E2H=0. Fortunately, we
already have this path to cope with fruity CPUs.

Tweak init_el2 to look at ID_AA64MMFR4_EL1.E2H0 first.

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20240122181344.258974-8-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index cab7f91949d8f58e9565dae545e1f0a1056ea14b..5bdafbcff00973657bbc0ec362768b77919f459e 100644 (file)
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -584,25 +584,32 @@ SYM_INNER_LABEL(init_el2, SYM_L_LOCAL)
        mov_q   x1, INIT_SCTLR_EL1_MMU_OFF
 
        /*
-        * Fruity CPUs seem to have HCR_EL2.E2H set to RES1,
-        * making it impossible to start in nVHE mode. Is that
-        * compliant with the architecture? Absolutely not!
+        * Compliant CPUs advertise their VHE-onlyness with
+        * ID_AA64MMFR4_EL1.E2H0 < 0. HCR_EL2.E2H can be
+        * RES1 in that case.
+        *
+        * Fruity CPUs seem to have HCR_EL2.E2H set to RES1, but
+        * don't advertise it (they predate this relaxation).
         */
+       mrs_s   x0, SYS_ID_AA64MMFR4_EL1
+       ubfx    x0, x0, #ID_AA64MMFR4_EL1_E2H0_SHIFT, #ID_AA64MMFR4_EL1_E2H0_WIDTH
+       tbnz    x0, #(ID_AA64MMFR4_EL1_E2H0_SHIFT + ID_AA64MMFR4_EL1_E2H0_WIDTH - 1), 1f
+
        mrs     x0, hcr_el2
        and     x0, x0, #HCR_E2H
-       cbz     x0, 1f
-
+       cbz     x0, 2f
+1:
        /* Set a sane SCTLR_EL1, the VHE way */
        pre_disable_mmu_workaround
        msr_s   SYS_SCTLR_EL12, x1
        mov     x2, #BOOT_CPU_FLAG_E2H
-       b       2f
+       b       3f
 
-1:
+2:
        pre_disable_mmu_workaround
        msr     sctlr_el1, x1
        mov     x2, xzr
-2:
+3:
        __init_el2_nvhe_prepare_eret
 
        mov     w0, #BOOT_CPU_MODE_EL2