Re: [PATCH 4/5] KVM: arm64: pkvm: Use direct function pointers for cpu_{on,resume}

Instead of using a boolean to decide whether a CPU is booting or
resuming, just pass an actual function pointer around.

This makes the code a bit more straightforward to understand.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/include/asm/kvm_asm.h     |  3 ++-
 arch/arm64/kvm/hyp/nvhe/hyp-init.S   |  9 +++----
 arch/arm64/kvm/hyp/nvhe/psci-relay.c | 39 +++++++++++++++++-----------
 3 files changed, 29 insertions(+), 22 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index a1ad12c72ebf1..f4c769857fdfc 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h

@@ -291,7 +291,8 @@ asmlinkage void __noreturn hyp_panic_bad_stack(void);
 asmlinkage void kvm_unexpected_el2_exception(void);
 struct kvm_cpu_context;
 void handle_trap(struct kvm_cpu_context *host_ctxt);
-asmlinkage void __noreturn __kvm_host_psci_cpu_entry(bool is_cpu_on);
+asmlinkage void __noreturn __kvm_host_psci_cpu_on_entry(void);
+asmlinkage void __noreturn __kvm_host_psci_cpu_resume_entry(void);
 void __noreturn __pkvm_init_finalise(void);
 void kvm_nvhe_prepare_backtrace(unsigned long fp, unsigned long pc);
 void kvm_patch_vector_branch(struct alt_instr *alt,

diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-init.S b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
index 2e80fcbff2dff..64296b31da73d 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-init.S
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-init.S

@@ -173,7 +173,7 @@ SYM_CODE_END(___kvm_hyp_init)
  * x0: struct kvm_nvhe_init_params PA
  */
 SYM_CODE_START(kvm_hyp_cpu_entry)
-       mov     x1, #1                          // is_cpu_on = true
+       ldr     x29, =__kvm_host_psci_cpu_on_entry
        b       __kvm_hyp_init_cpu

 /*

@@ -182,11 +182,10 @@ SYM_CODE_START(kvm_hyp_cpu_entry)
  * x0: struct kvm_nvhe_init_params PA
  */
 SYM_CODE_START(kvm_hyp_cpu_resume)
-       mov     x1, #0                          // is_cpu_on = false
+       ldr     x29, =__kvm_host_psci_cpu_resume_entry

 SYM_INNER_LABEL(__kvm_hyp_init_cpu, SYM_L_LOCAL)
        mov     x28, x0                         // Stash arguments
-       mov     x29, x1

        /* Check that the core was booted in EL2. */
        mrs     x0, CurrentEL

@@ -204,9 +203,7 @@ SYM_INNER_LABEL(__kvm_hyp_init_cpu, SYM_L_LOCAL)
        bl      ___kvm_hyp_init                 // Clobbers x0..x2

        /* Leave idmap -- using BLR is OK, LR is restored from host context */
-       mov     x0, x29
-       ldr     x1, =__kvm_host_psci_cpu_entry
-       blr     x1
+       blr     x29

        // The core booted in EL1, or the C code unexpectedly returned.
        // Either way, KVM cannot be initialized on it.

diff --git a/arch/arm64/kvm/hyp/nvhe/psci-relay.c b/arch/arm64/kvm/hyp/nvhe/psci-relay.c
index c3e196fb8b18f..cc698ceee9c8c 100644
--- a/arch/arm64/kvm/hyp/nvhe/psci-relay.c
+++ b/arch/arm64/kvm/hyp/nvhe/psci-relay.c

@@ -200,23 +200,12 @@ static int psci_system_suspend(u64 func_id, struct kvm_cpu_context *host_ctxt)
                         __hyp_pa(init_params), 0);
 }

-asmlinkage void __noreturn __kvm_host_psci_cpu_entry(bool is_cpu_on)
+static void __noreturn __kvm_host_psci_cpu_entry(unsigned long pc, unsigned long r0)
 {
-       struct psci_boot_args *boot_args;
-       struct kvm_cpu_context *host_ctxt;
-
-       host_ctxt = host_data_ptr(host_ctxt);
-
-       if (is_cpu_on)
-               boot_args = this_cpu_ptr(&cpu_on_args);
-       else
-               boot_args = this_cpu_ptr(&suspend_args);
-
-       cpu_reg(host_ctxt, 0) = boot_args->r0;
-       write_sysreg_el2(boot_args->pc, SYS_ELR);
+       struct kvm_cpu_context *host_ctxt = host_data_ptr(host_ctxt);

-       if (is_cpu_on)
-               release_boot_args(boot_args);
+       cpu_reg(host_ctxt, 0) = r0;
+       write_sysreg_el2(pc, SYS_ELR);

        write_sysreg_el1(INIT_SCTLR_EL1_MMU_OFF, SYS_SCTLR);
        write_sysreg(INIT_PSTATE_EL1, SPSR_EL2);

@@ -224,6 +213,26 @@ asmlinkage void __noreturn __kvm_host_psci_cpu_entry(bool is_cpu_on)
        __host_enter(host_ctxt);
 }

+asmlinkage void __noreturn __kvm_host_psci_cpu_on_entry(void)
+{
+       struct psci_boot_args *boot_args = this_cpu_ptr(&cpu_on_args);
+       unsigned long pc, r0;
+
+       pc = READ_ONCE(boot_args->pc);
+       r0 = READ_ONCE(boot_args->r0);
+
+       release_boot_args(boot_args);
+
+       __kvm_host_psci_cpu_entry(pc, r0);
+}
+
+asmlinkage void __noreturn __kvm_host_psci_cpu_resume_entry(void)
+{
+       struct psci_boot_args *boot_args = this_cpu_ptr(&cpu_on_args);