From mboxrd@z Thu Jan 1 00:00:00 1970 From: Antonios Motakis Subject: Re: [PATCH 2/2] KVM/arm: enable armv7 fp/simd lazy switch Date: Tue, 22 Sep 2015 16:01:05 +0200 Message-ID: <56015F21.60200@huawei.com> References: <1442538317-13618-1-git-send-email-m.smarduch@samsung.com> <1442538317-13618-3-git-send-email-m.smarduch@samsung.com> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: quoted-printable Cc: kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org To: Mario Smarduch , , , Return-path: In-Reply-To: <1442538317-13618-3-git-send-email-m.smarduch@samsung.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu List-Id: kvm.vger.kernel.org Hello, On 18-Sep-15 03:05, Mario Smarduch wrote: > Adds code to enable fp/simd lazy switch. On each entry check if fp/simd > registers have been switched to guest, if no set the trap flag. On trap = > switch fp/simd registers and set vfp_lazy to true and disable trapping. = > When the vcpu is about to be put, then context switch fp/simd registers > save guest and restore host and reset the vfp_lazy state to enable trappi= ng = > again. > = This description confused me a bit, since KVM on ARMv7 already exhibits lazy switching behavior for VFP. Should the description highlight the intended improvement in behavior? If I understand correctly, instead of restoring the host state on every exit, you postpone it until the task actually gets rescheduled, right? > Signed-off-by: Mario Smarduch > --- > arch/arm/kvm/arm.c | 17 +++++++++++++++++ > arch/arm/kvm/interrupts.S | 40 +++++++++++++++++++++++++++++----------- > 2 files changed, 46 insertions(+), 11 deletions(-) > = > diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c > index ce404a5..0acbb69 100644 > --- a/arch/arm/kvm/arm.c > +++ b/arch/arm/kvm/arm.c > @@ -105,6 +105,20 @@ void kvm_arch_check_processor_compat(void *rtn) > *(int *)rtn =3D 0; > } > = > +/** > + * kvm_switch_fp_regs() - switch guest/host VFP/SIMD registers > + * @vcpu: pointer to vcpu structure. > + * > + */ > +static void kvm_switch_fp_regs(struct kvm_vcpu *vcpu) > +{ > +#ifdef CONFIG_ARM > + if (vcpu->arch.vfp_lazy =3D=3D 1) { > + kvm_call_hyp(__kvm_restore_host_vfp_state, vcpu); > + vcpu->arch.vfp_lazy =3D 0; > + } > +#endif > +} > = > /** > * kvm_arch_init_vm - initializes a VM data structure > @@ -295,6 +309,9 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cp= u) > = > void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) > { > + /* Check if Guest accessed VFP registers */ > + kvm_switch_fp_regs(vcpu); > + > /* > * The arch-generic KVM code expects the cpu field of a vcpu to be -1 > * if the vcpu is no longer assigned to a cpu. This is used for the > diff --git a/arch/arm/kvm/interrupts.S b/arch/arm/kvm/interrupts.S > index 900ef6d..a47acc1 100644 > --- a/arch/arm/kvm/interrupts.S > +++ b/arch/arm/kvm/interrupts.S > @@ -96,6 +96,24 @@ ENTRY(__kvm_flush_vm_context) > bx lr > ENDPROC(__kvm_flush_vm_context) > = > +/** > + * void __kvm_restore_host_vfp_state(struct vcpu *vcpu) - Executes a lazy > + * fp/simd switch, saves the guest, restores host. > + * > + */ > +ENTRY(__kvm_restore_host_vfp_state) > + push {r3-r7} > + > + add r7, r0, #VCPU_VFP_GUEST > + store_vfp_state r7 > + > + add r7, r0, #VCPU_VFP_HOST > + ldr r7, [r7] > + restore_vfp_state r7 > + > + pop {r3-r7} > + bx lr > +ENDPROC(__kvm_restore_host_vfp_state) > = > /******************************************************************** > * Hypervisor world-switch code > @@ -131,7 +149,14 @@ ENTRY(__kvm_vcpu_run) > = > @ Trap coprocessor CRx accesses > set_hstr vmentry > + > + ldr r1, [vcpu, #VCPU_VFP_LAZY] > + cmp r1, #1 > + beq skip_guest_vfp_trap > + > set_hcptr vmentry, (HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11)) > +skip_guest_vfp_trap: I believe that HCPTR_TTA is not part of the floating point extensions. > + > set_hdcr vmentry > = > @ Write configured ID register into MIDR alias > @@ -170,22 +195,12 @@ __kvm_vcpu_return: > @ Don't trap coprocessor accesses for host kernel > set_hstr vmexit > set_hdcr vmexit > - set_hcptr vmexit, (HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11)), after_vf= p_restore > + set_hcptr vmexit, (HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11)) If you don't use the functionality of the macro to branch on change, then maybe the functionality should also be removed from the macro. > = > #ifdef CONFIG_VFPv3 > - @ Switch VFP/NEON hardware state to the host's > - add r7, vcpu, #VCPU_VFP_GUEST > - store_vfp_state r7 > - add r7, vcpu, #VCPU_VFP_HOST > - ldr r7, [r7] > - restore_vfp_state r7 > - > -after_vfp_restore: > @ Restore FPEXC_EN which we clobbered on entry > pop {r2} > VFPFMXR FPEXC, r2 > -#else > -after_vfp_restore: > #endif > = > @ Reset Hyp-role > @@ -485,6 +500,9 @@ switch_to_guest_vfp: > @ NEON/VFP used. Turn on VFP access. > set_hcptr vmtrap, (HCPTR_TCP(10) | HCPTR_TCP(11)) > = > + mov r1, #1 > + str r1, [vcpu, #VCPU_VFP_LAZY] > + > @ Switch VFP/NEON hardware state to the guest's > add r7, r0, #VCPU_VFP_HOST > ldr r7, [r7] > = -- = Antonios Motakis Virtualization Engineer Huawei Technologies Duesseldorf GmbH European Research Center Riesstrasse 25, 80992 M=FCnchen