KVM: arm64: Invoke FPSIMD context switch trap from C

The conversion of the FPSIMD context switch trap code to C has added
some overhead to calling it, due to the need to save registers that
the procedure call standard defines as caller-saved.

So, perhaps it is no longer worth invoking this trap handler quite
so early.

Instead, we can invoke it from fixup_guest_exit(), with little
likelihood of increasing the overhead much further.

As a convenience, this patch gives __hyp_switch_fpsimd() the same
return semantics fixup_guest_exit().  For now there is no
possibility of a spurious FPSIMD trap, so the function always
returns true, but this allows it to be tail-called with a single
return statement.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@arm.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

1 files changed, 0 insertions, 19 deletions

diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index bffece27b5c1..753b9d213651 100644
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -113,25 +113,6 @@ el1_hvc_guest:
 
 el1_trap:
 	get_vcpu_ptr	x1, x0
-
-	mrs		x0, esr_el2
-	lsr		x0, x0, #ESR_ELx_EC_SHIFT
-	/*
-	 * x0: ESR_EC
-	 * x1: vcpu pointer
-	 */
-
-	/*
-	 * We trap the first access to the FP/SIMD to save the host context
-	 * and restore the guest context lazily.
-	 * If FP/SIMD is not implemented, handle the trap and inject an
-	 * undefined instruction exception to the guest.
-	 */
-alternative_if_not ARM64_HAS_NO_FPSIMD
-	cmp	x0, #ESR_ELx_EC_FP_ASIMD
-	b.eq	__fpsimd_guest_restore
-alternative_else_nop_endif
-
 	mov	x0, #ARM_EXCEPTION_TRAP
 	b	__guest_exit