From 31a32b49b80f79cbb84a9c948c5609c6fc044443 Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Thu, 8 Apr 2021 14:10:09 +0100 Subject: [PATCH] arm64: Cope with CPUs stuck in VHE mode It seems that the CPUs part of the SoC known as Apple M1 have the terrible habit of being stuck with HCR_EL2.E2H==1, in violation of the architecture. Try and work around this deplorable state of affairs by detecting the stuck bit early and short-circuit the nVHE dance. Additional filtering code ensures that attempts at switching to nVHE from the command-line are also ignored. It is still unknown whether there are many more such nuggets to be found... Reported-by: Hector Martin Acked-by: Will Deacon Signed-off-by: Marc Zyngier Link: https://lore.kernel.org/r/20210408131010.1109027-3-maz@kernel.org Signed-off-by: Catalin Marinas --- arch/arm64/kernel/head.S | 39 +++++++++++++++++++++++++++--- arch/arm64/kernel/hyp-stub.S | 8 +++--- arch/arm64/kernel/idreg-override.c | 13 +++++++++- 3 files changed, 52 insertions(+), 8 deletions(-) diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index 840bda1869e9..96873dfa67fd 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -477,14 +477,13 @@ EXPORT_SYMBOL(kimage_vaddr) * booted in EL1 or EL2 respectively. */ SYM_FUNC_START(init_kernel_el) - mov_q x0, INIT_SCTLR_EL1_MMU_OFF - msr sctlr_el1, x0 - mrs x0, CurrentEL cmp x0, #CurrentEL_EL2 b.eq init_el2 SYM_INNER_LABEL(init_el1, SYM_L_LOCAL) + mov_q x0, INIT_SCTLR_EL1_MMU_OFF + msr sctlr_el1, x0 isb mov_q x0, INIT_PSTATE_EL1 msr spsr_el1, x0 @@ -504,9 +503,43 @@ SYM_INNER_LABEL(init_el2, SYM_L_LOCAL) msr vbar_el2, x0 isb + /* + * 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! + */ + mrs x0, hcr_el2 + and x0, x0, #HCR_E2H + cbz x0, 1f + + /* Switching to VHE requires a sane SCTLR_EL1 as a start */ + mov_q x0, INIT_SCTLR_EL1_MMU_OFF + msr_s SYS_SCTLR_EL12, x0 + + /* + * Force an eret into a helper "function", and let it return + * to our original caller... This makes sure that we have + * initialised the basic PSTATE state. + */ + mov x0, #INIT_PSTATE_EL2 + msr spsr_el1, x0 + adr x0, __cpu_stick_to_vhe + msr elr_el1, x0 + eret + +1: + mov_q x0, INIT_SCTLR_EL1_MMU_OFF + msr sctlr_el1, x0 + msr elr_el2, lr mov w0, #BOOT_CPU_MODE_EL2 eret + +__cpu_stick_to_vhe: + mov x0, #HVC_VHE_RESTART + hvc #0 + mov x0, #BOOT_CPU_MODE_EL2 + ret SYM_FUNC_END(init_kernel_el) /* diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S index 5eccbd62fec8..9c9b4d8fc395 100644 --- a/arch/arm64/kernel/hyp-stub.S +++ b/arch/arm64/kernel/hyp-stub.S @@ -27,12 +27,12 @@ SYM_CODE_START(__hyp_stub_vectors) ventry el2_fiq_invalid // FIQ EL2t ventry el2_error_invalid // Error EL2t - ventry el2_sync_invalid // Synchronous EL2h + ventry elx_sync // Synchronous EL2h ventry el2_irq_invalid // IRQ EL2h ventry el2_fiq_invalid // FIQ EL2h ventry el2_error_invalid // Error EL2h - ventry el1_sync // Synchronous 64-bit EL1 + ventry elx_sync // Synchronous 64-bit EL1 ventry el1_irq_invalid // IRQ 64-bit EL1 ventry el1_fiq_invalid // FIQ 64-bit EL1 ventry el1_error_invalid // Error 64-bit EL1 @@ -45,7 +45,7 @@ SYM_CODE_END(__hyp_stub_vectors) .align 11 -SYM_CODE_START_LOCAL(el1_sync) +SYM_CODE_START_LOCAL(elx_sync) cmp x0, #HVC_SET_VECTORS b.ne 1f msr vbar_el2, x1 @@ -71,7 +71,7 @@ SYM_CODE_START_LOCAL(el1_sync) 9: mov x0, xzr eret -SYM_CODE_END(el1_sync) +SYM_CODE_END(elx_sync) // nVHE? No way! Give me the real thing! SYM_CODE_START_LOCAL(mutate_to_vhe) diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c index be92fcd319a1..e628c8ce1ffe 100644 --- a/arch/arm64/kernel/idreg-override.c +++ b/arch/arm64/kernel/idreg-override.c @@ -29,11 +29,22 @@ struct ftr_set_desc { } fields[]; }; +static bool __init mmfr1_vh_filter(u64 val) +{ + /* + * If we ever reach this point while running VHE, we're + * guaranteed to be on one of these funky, VHE-stuck CPUs. If + * the user was trying to force nVHE on us, proceed with + * attitude adjustment. + */ + return !(is_kernel_in_hyp_mode() && val == 0); +} + static const struct ftr_set_desc mmfr1 __initconst = { .name = "id_aa64mmfr1", .override = &id_aa64mmfr1_override, .fields = { - { "vh", ID_AA64MMFR1_VHE_SHIFT }, + { "vh", ID_AA64MMFR1_VHE_SHIFT, mmfr1_vh_filter }, {} }, };