KVM: arm64: Initialize SCTLR_EL1 in __kvm_hyp_init_cpu()

When KVM is in protected mode, host calls to PSCI are proxied via EL2,
and cold entries from CPU_ON, CPU_SUSPEND, and SYSTEM_SUSPEND bounce
through __kvm_hyp_init_cpu() at EL2 before entering the host kernel's
entry point at EL1. While __kvm_hyp_init_cpu() initializes SPSR_EL2 for
the exception return to EL1, it does not initialize SCTLR_EL1.

Due to this, it's possible to enter EL1 with SCTLR_EL1 in an UNKNOWN
state. In practice this has been seen to result in kernel crashes after
CPU_ON as a result of SCTLR_EL1.M being 1 in violation of the initial
core configuration specified by PSCI.

Fix this by initializing SCTLR_EL1 for cold entry to the host kernel.
As it's necessary to write to SCTLR_EL12 in VHE mode, this
initialization is moved into __kvm_host_psci_cpu_entry() where we can
use write_sysreg_el1().

The remnants of the '__init_el2_nvhe_prepare_eret' macro are folded into
its only caller, as this is clearer than having the macro.

Fixes: cdf3671 ("KVM: arm64: Intercept host's CPU_ON SMCs")
Reported-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Ahmed Genidi <ahmed.genidi@arm.com>
[ Mark: clarify commit message, handle E2H, move to C, remove macro ]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Ahmed Genidi <ahmed.genidi@arm.com>
Cc: Ben Horgan <ben.horgan@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Leo Yan <leo.yan@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Leo Yan <leo.yan@arm.com>
Link: https://lore.kernel.org/r/20250227180526.1204723-3-mark.rutland@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/include/asm/el2_setup.h

@@ -270,11 +270,6 @@
 .Lskip_gcs_\@:
 .endm
 
-.macro __init_el2_nvhe_prepare_eret
-	mov	x0, #INIT_PSTATE_EL1
-	msr	spsr_el2, x0
-.endm
-
 .macro __init_el2_mpam
 	/* Memory Partitioning And Monitoring: disable EL2 traps */
 	mrs	x1, id_aa64pfr0_el1

arch/arm64/kernel/head.S

@@ -322,7 +322,8 @@ SYM_INNER_LABEL(init_el2, SYM_L_LOCAL)
 	msr	sctlr_el1, x1
 	mov	x2, xzr
 3:
-	__init_el2_nvhe_prepare_eret
+	mov	x0, #INIT_PSTATE_EL1
+	msr	spsr_el2, x0
 
 	mov	w0, #BOOT_CPU_MODE_EL2
 	orr	x0, x0, x2

arch/arm64/kvm/hyp/nvhe/hyp-init.S

@@ -214,8 +214,6 @@ SYM_CODE_START_LOCAL(__kvm_hyp_init_cpu)
 
 	bl	__kvm_init_el2_state
 
-	__init_el2_nvhe_prepare_eret
-
 	/* Enable MMU, set vectors and stack. */
 	mov	x0, x28
 	bl	___kvm_hyp_init			// Clobbers x0..x2

arch/arm64/kvm/hyp/nvhe/psci-relay.c

@@ -218,6 +218,9 @@ asmlinkage void __noreturn __kvm_host_psci_cpu_entry(bool is_cpu_on)
 	if (is_cpu_on)
 		release_boot_args(boot_args);
 
+	write_sysreg_el1(INIT_SCTLR_EL1_MMU_OFF, SYS_SCTLR);
+	write_sysreg(INIT_PSTATE_EL1, SPSR_EL2);
+
 	__host_enter(host_ctxt);
 }