From: alex.bennee@linaro•org (Alex Bennée)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v10 18/18] KVM: arm64: Invoke FPSIMD context switch trap from C
Date: Thu, 24 May 2018 16:09:04 +0100 [thread overview]
Message-ID: <87vabdrsz3.fsf@linaro.org> (raw)
In-Reply-To: <1527005119-6842-19-git-send-email-Dave.Martin@arm.com>
Dave Martin <Dave.Martin@arm•com> 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@arm•com>
> Reviewed-by: Marc Zyngier <marc.zyngier@arm•com>
> Reviewed-by: Christoffer Dall <christoffer.dall@arm•com>
Reviewed-by: Alex Benn?e <alex.bennee@linaro•org>
> ---
> 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 Benn?e
prev parent reply other threads:[~2018-05-24 15:09 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-22 16:05 [PATCH v10 00/18] KVM: arm64: Optimise FPSIMD context switching Dave Martin
2018-05-22 16:05 ` [PATCH v10 01/18] arm64: fpsimd: Fix TIF_FOREIGN_FPSTATE after invalidating cpu regs Dave Martin
2018-05-23 11:33 ` Christoffer Dall
2018-05-23 13:44 ` Alex Bennée
2018-05-23 13:46 ` Catalin Marinas
2018-05-22 16:05 ` [PATCH v10 02/18] thread_info: Add update_thread_flag() helpers Dave Martin
2018-05-23 13:46 ` Alex Bennée
2018-05-23 13:57 ` Dave Martin
2018-05-23 14:35 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 03/18] arm64: Use update{,_tsk}_thread_flag() Dave Martin
2018-05-23 13:48 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 04/18] KVM: arm/arm64: Introduce kvm_arch_vcpu_run_pid_change Dave Martin
2018-05-23 14:34 ` Alex Bennée
2018-05-23 14:40 ` Dave Martin
2018-05-24 8:11 ` Christoffer Dall
2018-05-24 9:18 ` Alex Bennée
2018-05-24 10:04 ` Dave Martin
2018-05-22 16:05 ` [PATCH v10 05/18] KVM: arm64: Convert lazy FPSIMD context switch trap to C Dave Martin
2018-05-23 19:35 ` Alex Bennée
2018-05-24 8:12 ` Christoffer Dall
2018-05-24 8:54 ` Dave Martin
2018-05-24 9:14 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 06/18] arm64: fpsimd: Generalise context saving for non-task contexts Dave Martin
2018-05-23 20:15 ` Alex Bennée
2018-05-24 9:03 ` Dave Martin
2018-05-24 9:41 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 07/18] arm64: fpsimd: Eliminate task->mm checks Dave Martin
2018-05-23 11:48 ` Christoffer Dall
2018-05-23 13:31 ` Dave Martin
2018-05-23 14:56 ` Catalin Marinas
2018-05-23 15:03 ` Dave Martin
2018-05-23 16:42 ` Catalin Marinas
2018-05-24 8:33 ` Christoffer Dall
2018-05-24 9:16 ` Alex Bennée
2018-05-24 9:50 ` Dave Martin
2018-05-24 10:06 ` Christoffer Dall
2018-05-24 14:37 ` Dave Martin
2018-05-25 9:00 ` Christoffer Dall
2018-05-25 9:45 ` Dave Martin
2018-05-25 11:28 ` Christoffer Dall
2018-05-24 9:19 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 08/18] arm64/sve: Refactor user SVE trap maintenance for external use Dave Martin
2018-05-23 20:16 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 09/18] KVM: arm64: Repurpose vcpu_arch.debug_flags for general-purpose flags Dave Martin
2018-05-24 9:21 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 10/18] KVM: arm64: Optimise FPSIMD handling to reduce guest/host thrashing Dave Martin
2018-05-24 10:09 ` Alex Bennée
2018-05-24 10:18 ` Dave Martin
2018-05-22 16:05 ` [PATCH v10 11/18] arm64/sve: Move read_zcr_features() out of cpufeature.h Dave Martin
2018-05-24 10:12 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 12/18] arm64/sve: Switch sve_pffr() argument from task to thread Dave Martin
2018-05-24 10:12 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 13/18] arm64/sve: Move sve_pffr() to fpsimd.h and make inline Dave Martin
2018-05-24 10:20 ` Alex Bennée
2018-05-24 11:22 ` Dave Martin
2018-05-22 16:05 ` [PATCH v10 14/18] KVM: arm64: Save host SVE context as appropriate Dave Martin
2018-05-23 14:59 ` Catalin Marinas
2018-05-24 9:11 ` Christoffer Dall
2018-05-24 14:49 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 15/18] KVM: arm64: Remove eager host SVE state saving Dave Martin
2018-05-24 14:54 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 16/18] KVM: arm64: Remove redundant *exit_code changes in fpsimd_guest_exit() Dave Martin
2018-05-24 9:11 ` Christoffer Dall
2018-05-24 15:02 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 17/18] KVM: arm64: Fold redundant exit code checks out of fixup_guest_exit() Dave Martin
2018-05-24 9:12 ` Christoffer Dall
2018-05-24 15:06 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 18/18] KVM: arm64: Invoke FPSIMD context switch trap from C Dave Martin
2018-05-24 15:09 ` Alex Bennée [this message]
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