Commit cf412b00 authored by Dave Martin's avatar Dave Martin Committed by Marc Zyngier
Browse files

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: default avatarDave Martin <Dave.Martin@arm.com>
Reviewed-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
Reviewed-by: default avatarChristoffer Dall <christoffer.dall@arm.com>
Reviewed-by: default avatarAlex Bennée <alex.bennee@linaro.org>
Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
parent 7846b311

arch/arm64/kvm/hyp/entry.S

+0 −30
Original line number Diff line number Diff line
@@ -166,33 +166,3 @@ abort_guest_exit_end: 
	orr	x0, x0, x5

1:	ret

ENDPROC(__guest_exit)
 


ENTRY(__fpsimd_guest_restore)

	// x0: esr

	// x1: vcpu

	// x2-x29,lr: vcpu regs

	// vcpu x0-x1 on the stack

	stp	x2, x3, [sp, #-144]!

	stp	x4, x5, [sp, #16]

	stp	x6, x7, [sp, #32]

	stp	x8, x9, [sp, #48]

	stp	x10, x11, [sp, #64]

	stp	x12, x13, [sp, #80]

	stp	x14, x15, [sp, #96]

	stp	x16, x17, [sp, #112]

	stp	x18, lr, [sp, #128]



	bl	__hyp_switch_fpsimd



	ldp	x4, x5, [sp, #16]

	ldp	x6, x7, [sp, #32]

	ldp	x8, x9, [sp, #48]

	ldp	x10, x11, [sp, #64]

	ldp	x12, x13, [sp, #80]

	ldp	x14, x15, [sp, #96]

	ldp	x16, x17, [sp, #112]

	ldp	x18, lr, [sp, #128]

	ldp	x0, x1, [sp, #144]

	ldp	x2, x3, [sp], #160

	eret

ENDPROC(__fpsimd_guest_restore)

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

+0 −19
Original line number Diff line number Diff line
@@ -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

arch/arm64/kvm/hyp/switch.c

+13 −2
Original line number Diff line number Diff line
@@ -328,8 +328,7 @@ static bool __hyp_text __skip_instr(struct kvm_vcpu *vcpu) 
	}

}



void __hyp_text __hyp_switch_fpsimd(u64 esr __always_unused,

				    struct kvm_vcpu *vcpu)

static bool __hyp_text __hyp_switch_fpsimd(struct kvm_vcpu *vcpu)

{

	struct user_fpsimd_state *host_fpsimd = vcpu->arch.host_fpsimd_state;
@@ -369,6 +368,8 @@ void __hyp_text __hyp_switch_fpsimd(u64 esr __always_unused, 
			     fpexc32_el2);



	vcpu->arch.flags |= KVM_ARM64_FP_ENABLED;



	return true;

}



/*
@@ -390,6 +391,16 @@ static bool __hyp_text fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code) 
	if (*exit_code != ARM_EXCEPTION_TRAP)

		goto exit;



	/*

	 * 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.

	 */

	if (system_supports_fpsimd() &&

	    kvm_vcpu_trap_get_class(vcpu) == ESR_ELx_EC_FP_ASIMD)

		return __hyp_switch_fpsimd(vcpu);



	if (!__populate_fault_info(vcpu))

		return true;

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