KVM: arm64: Fix __pkvm_init_switch_pgd call ABI

Fix the mismatch between the (incorrect) C signature, C call site, and
asm implementation by aligning all three on an API passing the
parameters (pgd and SP) separately, instead of as a bundled struct.

Remove the now unnecessary memory accesses while the MMU is off from the
asm, which simplifies the C caller (as it does not need to convert a VA
struct pointer to PA) and makes the code slightly more robust by
offsetting the struct fields from C and properly expressing the call to
the C compiler (e.g. type checker and kCFI).

Fixes: f320bc74 ("KVM: arm64: Prepare the creation of s1 mappings at EL2")
Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20240610063244.2828978-3-ptosi@google.comSigned-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/include/asm/kvm_hyp.h

@@ -124,8 +124,8 @@ void __noreturn __hyp_do_panic(struct kvm_cpu_context *host_ctxt, u64 spsr,
 #endif
 
 #ifdef __KVM_NVHE_HYPERVISOR__
-void __pkvm_init_switch_pgd(phys_addr_t phys, unsigned long size,
-			    phys_addr_t pgd, void *sp, void *cont_fn);
+void __pkvm_init_switch_pgd(phys_addr_t pgd, unsigned long sp,
+		void (*fn)(void));
 int __pkvm_init(phys_addr_t phys, unsigned long size, unsigned long nr_cpus,
 		unsigned long *per_cpu_base, u32 hyp_va_bits);
 void __noreturn __host_enter(struct kvm_cpu_context *host_ctxt);

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

@@ -265,33 +265,35 @@ alternative_else_nop_endif
 
 SYM_CODE_END(__kvm_handle_stub_hvc)
 
+/*
+ * void __pkvm_init_switch_pgd(phys_addr_t pgd, unsigned long sp,
+ *                             void (*fn)(void));
+ */
 SYM_FUNC_START(__pkvm_init_switch_pgd)
 	/* Turn the MMU off */
 	pre_disable_mmu_workaround
-	mrs	x2, sctlr_el2
-	bic	x3, x2, #SCTLR_ELx_M
-	msr	sctlr_el2, x3
+	mrs	x3, sctlr_el2
+	bic	x4, x3, #SCTLR_ELx_M
+	msr	sctlr_el2, x4
 	isb
 
 	tlbi	alle2
 
 	/* Install the new pgtables */
-	ldr	x3, [x0, #NVHE_INIT_PGD_PA]
-	phys_to_ttbr x4, x3
+	phys_to_ttbr x5, x0
 alternative_if ARM64_HAS_CNP
-	orr	x4, x4, #TTBR_CNP_BIT
+	orr	x5, x5, #TTBR_CNP_BIT
 alternative_else_nop_endif
-	msr	ttbr0_el2, x4
+	msr	ttbr0_el2, x5
 
 	/* Set the new stack pointer */
-	ldr	x0, [x0, #NVHE_INIT_STACK_HYP_VA]
-	mov	sp, x0
+	mov	sp, x1
 
 	/* And turn the MMU back on! */
 	dsb	nsh
 	isb
-	set_sctlr_el2	x2
-	ret	x1
+	set_sctlr_el2	x3
+	ret	x2
 SYM_FUNC_END(__pkvm_init_switch_pgd)
 
 	.popsection

arch/arm64/kvm/hyp/nvhe/setup.c

@@ -339,7 +339,7 @@ int __pkvm_init(phys_addr_t phys, unsigned long size, unsigned long nr_cpus,
 {
 	struct kvm_nvhe_init_params *params;
 	void *virt = hyp_phys_to_virt(phys);
-	void (*fn)(phys_addr_t params_pa, void *finalize_fn_va);
+	typeof(__pkvm_init_switch_pgd) *fn;
 	int ret;
 
 	BUG_ON(kvm_check_pvm_sysreg_table());
@@ -363,7 +363,7 @@ int __pkvm_init(phys_addr_t phys, unsigned long size, unsigned long nr_cpus,
 	/* Jump in the idmap page to switch to the new page-tables */
 	params = this_cpu_ptr(&kvm_init_params);
 	fn = (typeof(fn))__hyp_pa(__pkvm_init_switch_pgd);
-	fn(__hyp_pa(params), __pkvm_init_finalise);
+	fn(params->pgd_pa, params->stack_hyp_va, __pkvm_init_finalise);
 
 	unreachable();
 }