Dave Martin <Dave.Martin@xxxxxxx> writes:
> 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@xxxxxxx>
> Reviewed-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> Reviewed-by: Christoffer Dall <christoffer.dall@xxxxxxx>
Reviewed-by: Alex Bennée <alex.bennee@xxxxxxxxxx>
> ---
> arch/arm64/kvm/hyp/entry.S | 30 ------------------------------
> arch/arm64/kvm/hyp/hyp-entry.S | 19 -------------------
> arch/arm64/kvm/hyp/switch.c | 15 +++++++++++++--
> 3 files changed, 13 insertions(+), 51 deletions(-)
>
> diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
> index 40f349b..fad1e16 100644
> --- a/arch/arm64/kvm/hyp/entry.S
> +++ b/arch/arm64/kvm/hyp/entry.S
> @@ -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)
> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
> index bffece2..753b9d2 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
>
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index 4fbee95..2d45bd7 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -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;
--
Alex Bennée
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