KVM: arm64: Don't populate TPIDR_EL2 in finalise_el2()

When running with VHE, TPIDR_EL2 is only used for the percpu offset once the ARM64_HAS_VIRT_HOST_EXTN capability has been detected, at which point cpu_copy_el2regs() will populate its contents from TPIDR_EL1.

Remove the redundant initialisation of TPIDR_EL2 from finalise_el2().

---

I spotted this by inspection as part of an ill-fated (abandoned) attempt at repurposing tpidr_elx for something else.

 arch/arm64/kernel/hyp-stub.S | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

index 085bc9972f6b..8b8614c0b9a5 100644
@@ -105,11 +105,9 @@ SYM_CODE_START_LOCAL(__finalise_el2)
 	msr_hcr_el2 x0
 	isb
 
-	// Use the EL1 allocated stack, per-cpu offset
+	// Use the EL1 allocated stack
 	mrs	x0, sp_el1
 	mov	sp, x0
-	mrs	x0, tpidr_el1
-	msr	tpidr_el2, x0
 
 	// FP configuration, vectors
 	mrs_s	x0, SYS_CPACR_EL12

2.53.0.1018.g2bb0e51243-goog

It wasn't clear to me how this worked for both the boot CPU and secondaries, since they both call finalise_el2(). How about a slightly more elaborate commit message, e.g.

| Currently, it is not necessary for __finalise_el2() to configure
| TPIDR_EL2:
|
| * The hyp stub code does not consume the value of TPIDR_EL2.
|
| * On the boot cpu, TPIDR_EL1 is used for the percpu offset until the
|   ARM64_HAS_VIRT_HOST_EXTN cpucap is detected and boot alternatives
|   are patched. Before boot alternatives are patched,
|   cpu_copy_el2regs() will copy TPIDR_EL1 into TPIDR_EL2. It is not
|   necessary for __finalise_el2() to initialise TPIDR_EL2 before this.
|
| * Secondary CPUs are brought up after boot alternatives have been
|   patched, and __secondary_switched() will initialize TPIDR_EL2 in
|   'init_cpu_task', after finalise_el2() calls __finalise_el2()
|
| * KVM hyp code which may consume TPIDR_EL2 is brought up after all
|   secondaries have been booted, once TPIDR_El2 has been configured on
|   all CPUs.
|
| Remove the redundant initialisation from __finalise_el2().

Mark.