arm64: KVM: Simplify HYP init/teardown

Now that we only have the "merged page tables" case to deal with,
there is a bunch of things we can simplify in the HYP code (both
at init and teardown time).

Signed-off-by: Marc Zyngier <[e-mail]>
Signed-off-by: Christoffer Dall <[e-mail]>

arch/arm64/include/asm/kvm_host.h

···
 int __attribute_const__ kvm_target_cpu(void);
 int kvm_reset_vcpu(struct kvm_vcpu *vcpu);
 int kvm_arch_dev_ioctl_check_extension(long ext);
-unsigned long kvm_hyp_reset_entry(void);
 void __extended_idmap_trampoline(phys_addr_t boot_pgd, phys_addr_t idmap_start);
 
 struct kvm_arch {
···
 	 * Call initialization code, and switch to the full blown
 	 * HYP code.
 	 */
-	__kvm_call_hyp((void *)boot_pgd_ptr, pgd_ptr,
-		       hyp_stack_ptr, vector_ptr);
+	__kvm_call_hyp((void *)pgd_ptr, hyp_stack_ptr, vector_ptr);
 }
 
+void __kvm_hyp_teardown(void);
 static inline void __cpu_reset_hyp_mode(phys_addr_t boot_pgd_ptr,
 					phys_addr_t phys_idmap_start)
 {
-	/*
-	 * Call reset code, and switch back to stub hyp vectors.
-	 * Uses __kvm_call_hyp() to avoid kaslr's kvm_ksym_ref() translation.
-	 */
-	__kvm_call_hyp((void *)kvm_hyp_reset_entry(),
-		       boot_pgd_ptr, phys_idmap_start);
+	kvm_call_hyp(__kvm_hyp_teardown, phys_idmap_start);
 }
 
 static inline void kvm_arch_hardware_unsetup(void) {}

arch/arm64/kvm/hyp-init.S

···
 	b	.
 
 	/*
-	 * x0: HYP boot pgd
-	 * x1: HYP pgd
-	 * x2: HYP stack
-	 * x3: HYP vectors
+	 * x0: HYP pgd
+	 * x1: HYP stack
+	 * x2: HYP vectors
 	 */
 __do_hyp_init:
 
···
 	msr	sctlr_el2, x4
 	isb
 
-	/* Skip the trampoline dance if we merged the boot and runtime PGDs */
-	cmp	x0, x1
-	b.eq	merged
-
-	/* MMU is now enabled. Get ready for the trampoline dance */
-	ldr	x4, =TRAMPOLINE_VA
-	adr	x5, target
-	bfi	x4, x5, #0, #PAGE_SHIFT
-	br	x4
-
-target: /* We're now in the trampoline code, switch page tables */
-	msr	ttbr0_el2, x1
-	isb
-
-	/* Invalidate the old TLBs */
-	tlbi	alle2
-	dsb	sy
-
-merged:
 	/* Set the stack and new vectors */
+	kern_hyp_va	x1
+	mov	sp, x1
 	kern_hyp_va	x2
-	mov	sp, x2
-	kern_hyp_va	x3
-	msr	vbar_el2, x3
+	msr	vbar_el2, x2
 
 	/* Hello, World! */
 	eret
 ENDPROC(__kvm_hyp_init)
 
 	/*
-	 * Reset kvm back to the hyp stub. This is the trampoline dance in
-	 * reverse. If kvm used an extended idmap, __extended_idmap_trampoline
-	 * calls this code directly in the idmap. In this case switching to the
-	 * boot tables is a no-op.
-	 *
-	 * x0: HYP boot pgd
-	 * x1: HYP phys_idmap_start
+	 * Reset kvm back to the hyp stub.
 	 */
 ENTRY(__kvm_hyp_reset)
-	/* We're in trampoline code in VA, switch back to boot page tables */
-	msr	ttbr0_el2, x0
-	isb
-
-	/* Ensure the PA branch doesn't find a stale tlb entry or stale code. */
-	ic	iallu
-	tlbi	alle2
-	dsb	sy
-	isb
-
-	/* Branch into PA space */
-	adr	x0, 1f
-	bfi	x1, x0, #0, #PAGE_SHIFT
-	br	x1
-
 	/* We're now in idmap, disable MMU */
-1:	mrs	x0, sctlr_el2
+	mrs	x0, sctlr_el2
 	ldr	x1, =SCTLR_ELx_FLAGS
 	bic	x0, x0, x1		// Clear SCTL_M and etc
 	msr	sctlr_el2, x0
 	isb
-
-	/* Invalidate the old TLBs */
-	tlbi	alle2
-	dsb	sy
 
 	/* Install stub vectors */
 	adr_l	x0, __hyp_stub_vectors

arch/arm64/kvm/hyp/entry.S

···
 
 	eret
 ENDPROC(__fpsimd_guest_restore)
-
-/*
- * When using the extended idmap, we don't have a trampoline page we can use
- * while we switch pages tables during __kvm_hyp_reset. Accessing the idmap
- * directly would be ideal, but if we're using the extended idmap then the
- * idmap is located above HYP_PAGE_OFFSET, and the address will be masked by
- * kvm_call_hyp using kern_hyp_va.
- *
- * x0: HYP boot pgd
- * x1: HYP phys_idmap_start
- */
-ENTRY(__extended_idmap_trampoline)
-	mov	x4, x1
-	adr_l	x3, __kvm_hyp_reset
-
-	/* insert __kvm_hyp_reset()s offset into phys_idmap_start */
-	bfi	x4, x3, #0, #PAGE_SHIFT
-	br	x4
-ENDPROC(__extended_idmap_trampoline)

arch/arm64/kvm/hyp/hyp-entry.S

···
 	isb
 	ret
 ENDPROC(__vhe_hyp_call)
+
+/*
+ * Compute the idmap address of __kvm_hyp_reset based on the idmap
+ * start passed as a parameter, and jump there.
+ *
+ * x0: HYP phys_idmap_start
+ */
+ENTRY(__kvm_hyp_teardown)
+	mov	x4, x0
+	adr_l	x3, __kvm_hyp_reset
+
+	/* insert __kvm_hyp_reset()s offset into phys_idmap_start */
+	bfi	x4, x3, #0, #PAGE_SHIFT
+	br	x4
+ENDPROC(__kvm_hyp_teardown)
 	
 el1_sync:				// Guest trapped into EL2
 	save_x0_to_x3

arch/arm64/kvm/reset.c

···
 	/* Reset timer */
 	return kvm_timer_vcpu_reset(vcpu, cpu_vtimer_irq);
 }
-
-unsigned long kvm_hyp_reset_entry(void)
-{
-	/*
-	 * KVM is running with merged page tables, which don't have the
-	 * trampoline page mapped. We know the idmap is still mapped,
-	 * but can't be called into directly. Use
-	 * __extended_idmap_trampoline to do the call.
-	 */
-	return (unsigned long)kvm_ksym_ref(__extended_idmap_trampoline);
-}