KVM: arm64: Shave a few bytes from the EL2 idmap code

Our idmap is becoming too big, to the point where it doesn't fit in
a 4kB page anymore.

There are some low-hanging fruits though, such as the el2_init_state
horror that is expanded 3 times in the kernel. Let's at least limit
ourselves to two copies, which makes the kernel link again.

At some point, we'll have to have a better way of doing this.

Reported-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20241009204903.GA3353168@thelio-3990X

arch/arm64/include/asm/kvm_asm.h

@@ -178,6 +178,7 @@ struct kvm_nvhe_init_params {
 	unsigned long hcr_el2;
 	unsigned long vttbr;
 	unsigned long vtcr;
+	unsigned long tmp;
 };
 
 /*

arch/arm64/kernel/asm-offsets.c

@@ -146,6 +146,7 @@ int main(void)
   DEFINE(NVHE_INIT_HCR_EL2,	offsetof(struct kvm_nvhe_init_params, hcr_el2));
   DEFINE(NVHE_INIT_VTTBR,	offsetof(struct kvm_nvhe_init_params, vttbr));
   DEFINE(NVHE_INIT_VTCR,	offsetof(struct kvm_nvhe_init_params, vtcr));
+  DEFINE(NVHE_INIT_TMP,		offsetof(struct kvm_nvhe_init_params, tmp));
 #endif
 #ifdef CONFIG_CPU_PM
   DEFINE(CPU_CTX_SP,		offsetof(struct cpu_suspend_ctx, sp));

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

@@ -24,28 +24,25 @@
 	.align	11
 
 SYM_CODE_START(__kvm_hyp_init)
-	ventry	__invalid		// Synchronous EL2t
-	ventry	__invalid		// IRQ EL2t
-	ventry	__invalid		// FIQ EL2t
-	ventry	__invalid		// Error EL2t
+	ventry	.			// Synchronous EL2t
+	ventry	.			// IRQ EL2t
+	ventry	.			// FIQ EL2t
+	ventry	.			// Error EL2t
 
-	ventry	__invalid		// Synchronous EL2h
-	ventry	__invalid		// IRQ EL2h
-	ventry	__invalid		// FIQ EL2h
-	ventry	__invalid		// Error EL2h
+	ventry	.			// Synchronous EL2h
+	ventry	.			// IRQ EL2h
+	ventry	.			// FIQ EL2h
+	ventry	.			// Error EL2h
 
 	ventry	__do_hyp_init		// Synchronous 64-bit EL1
-	ventry	__invalid		// IRQ 64-bit EL1
-	ventry	__invalid		// FIQ 64-bit EL1
-	ventry	__invalid		// Error 64-bit EL1
+	ventry	.			// IRQ 64-bit EL1
+	ventry	.			// FIQ 64-bit EL1
+	ventry	.			// Error 64-bit EL1
 
-	ventry	__invalid		// Synchronous 32-bit EL1
-	ventry	__invalid		// IRQ 32-bit EL1
-	ventry	__invalid		// FIQ 32-bit EL1
-	ventry	__invalid		// Error 32-bit EL1
-
-__invalid:
-	b	.
+	ventry	.			// Synchronous 32-bit EL1
+	ventry	.			// IRQ 32-bit EL1
+	ventry	.			// FIQ 32-bit EL1
+	ventry	.			// Error 32-bit EL1
 
 	/*
 	 * Only uses x0..x3 so as to not clobber callee-saved SMCCC registers.
@@ -76,6 +73,13 @@ __do_hyp_init:
 	eret
 SYM_CODE_END(__kvm_hyp_init)
 
+SYM_CODE_START_LOCAL(__kvm_init_el2_state)
+	/* Initialize EL2 CPU state to sane values. */
+	init_el2_state				// Clobbers x0..x2
+	finalise_el2_state
+	ret
+SYM_CODE_END(__kvm_init_el2_state)
+
 /*
  * Initialize the hypervisor in EL2.
  *
@@ -102,9 +106,12 @@ SYM_CODE_START_LOCAL(___kvm_hyp_init)
 	// TPIDR_EL2 is used to preserve x0 across the macro maze...
 	isb
 	msr	tpidr_el2, x0
-	init_el2_state
-	finalise_el2_state
+	str	lr, [x0, #NVHE_INIT_TMP]
+
+	bl	__kvm_init_el2_state
+
 	mrs	x0, tpidr_el2
+	ldr	lr, [x0, #NVHE_INIT_TMP]
 
 1:
 	ldr	x1, [x0, #NVHE_INIT_TPIDR_EL2]
@@ -199,9 +206,8 @@ SYM_CODE_START_LOCAL(__kvm_hyp_init_cpu)
 
 2:	msr	SPsel, #1			// We want to use SP_EL{1,2}
 
-	/* Initialize EL2 CPU state to sane values. */
-	init_el2_state				// Clobbers x0..x2
-	finalise_el2_state
+	bl	__kvm_init_el2_state
+
 	__init_el2_nvhe_prepare_eret
 
 	/* Enable MMU, set vectors and stack. */