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 <marcan@marcan.st>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210408131010.1109027-3-maz@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 12 insertions, 1 deletions

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 },
 		{}
 	},
 };