From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mario Smarduch Subject: Re: [PATCH v6 1/6] arm/arm64: KVM: Introduce armv7 fp/simd vcpu fields and helpers Date: Fri, 15 Jan 2016 17:21:23 -0800 Message-ID: <56999B13.6050103@samsung.com> References: <1451166900-3711-1-git-send-email-m.smarduch@samsung.com> <1451166900-3711-2-git-send-email-m.smarduch@samsung.com> <20160110163204.GD30867@cbox> <56943D29.3000002@samsung.com> <20160112141207.GF15554@cbox> <5695A0EB.5020609@samsung.com> <56970FE8.4020805@samsung.com> <20160114132718.GA4329@cbox> <5698531E.1090606@samsung.com> <5698B5C9.4030404@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Russell King - ARM Linux To: Marc Zyngier , Christoffer Dall Return-path: Received: from mailout3.w2.samsung.com ([211.189.100.13]:30419 "EHLO usmailout3.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755061AbcAPBV0 (ORCPT ); Fri, 15 Jan 2016 20:21:26 -0500 Received: from uscpsbgm1.samsung.com (u114.gpu85.samsung.co.kr [203.254.195.114]) by usmailout3.samsung.com (Oracle Communications Messaging Server 7.0.5.31.0 64bit (built May 5 2014)) with ESMTP id <0O1000NEDUFO1660@usmailout3.samsung.com> for kvm@vger.kernel.org; Fri, 15 Jan 2016 20:21:24 -0500 (EST) In-reply-to: <5698B5C9.4030404@arm.com> Sender: kvm-owner@vger.kernel.org List-ID: On 1/15/2016 1:03 AM, Marc Zyngier wrote: > On 15/01/16 02:02, Mario Smarduch wrote: >> >> >> On 1/14/2016 5:27 AM, Christoffer Dall wrote: >>> On Wed, Jan 13, 2016 at 07:03:04PM -0800, Mario Smarduch wrote: >>>> >>>> >>>> On 1/12/2016 4:57 PM, Mario Smarduch wrote: >>>>> >>>>> >>>>> On 1/12/2016 6:12 AM, Christoffer Dall wrote: >>>>>> On Mon, Jan 11, 2016 at 03:39:21PM -0800, Mario Smarduch wrote: >>>>>>> >>>>>>> >>>>>>> On 1/10/2016 8:32 AM, Christoffer Dall wrote: >>>>>>>> Hi Mario, >>>>>>>> >>>>>>>> I spotted one more potential issue... >>>>>>>> >>>>>>>> On Sat, Dec 26, 2015 at 01:54:55PM -0800, Mario Smarduch wrote: >>>>>>>>> Add helper functions to enable access to fp/smid on guest entry and save host >>>>>>>>> fpexc on vcpu put, check if fp/simd registers are dirty and add new vcpu >>>>>>>>> fields. >>>>>>>>> >>>>>>>>> Signed-off-by: Mario Smarduch >>>>>>>>> --- >>>>>>>>> arch/arm/include/asm/kvm_emulate.h | 42 ++++++++++++++++++++++++++++++++++++ >>>>>>>>> arch/arm/include/asm/kvm_host.h | 6 ++++++ >>>>>>>>> arch/arm64/include/asm/kvm_emulate.h | 8 +++++++ >>>>>>>>> 3 files changed, 56 insertions(+) >>>>>>>>> >>>>>>>>> diff --git a/arch/arm/include/asm/kvm_emulate.h b/arch/arm/include/asm/kvm_emulate.h >>>>>>>>> index 3095df0..d4d9da1 100644 >>>>>>>>> --- a/arch/arm/include/asm/kvm_emulate.h >>>>>>>>> +++ b/arch/arm/include/asm/kvm_emulate.h >>>>>>>>> @@ -24,6 +24,8 @@ >>>>>>>>> #include >>>>>>>>> #include >>>>>>>>> #include >>>>>>>>> +#include >>>>>>>>> +#include "../vfp/vfpinstr.h" >>>>>>>>> >>>>>>>>> unsigned long *vcpu_reg(struct kvm_vcpu *vcpu, u8 reg_num); >>>>>>>>> unsigned long *vcpu_spsr(struct kvm_vcpu *vcpu); >>>>>>>>> @@ -255,4 +257,44 @@ static inline unsigned long vcpu_data_host_to_guest(struct kvm_vcpu *vcpu, >>>>>>>>> } >>>>>>>>> } >>>>>>>>> >>>>>>>>> +#ifdef CONFIG_VFPv3 >>>>>>>>> +/* Called from vcpu_load - save fpexc and enable guest access to fp/simd unit */ >>>>>>>>> +static inline void vcpu_trap_vfp_enable(struct kvm_vcpu *vcpu) >>>>>>>>> +{ >>>>>>>>> + u32 fpexc; >>>>>>>>> + >>>>>>>>> + /* Save host fpexc, and enable guest access to fp unit */ >>>>>>>>> + fpexc = fmrx(FPEXC); >>>>>>>>> + vcpu->arch.host_fpexc = fpexc; >>>>>>>>> + fpexc |= FPEXC_EN; >>>>>>>>> + fmxr(FPEXC, fpexc); >>>>>>>>> + >>>>>>>>> + /* Configure HCPTR to trap on tracing and fp/simd access */ >>>>>>>>> + vcpu->arch.hcptr = HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11); >>>>>>>>> +} >>>>>>>>> + >>>>>>>>> +/* Called from vcpu_put - restore host fpexc */ >>>>>>>>> +static inline void vcpu_restore_host_fpexc(struct kvm_vcpu *vcpu) >>>>>>>>> +{ >>>>>>>>> + fmxr(FPEXC, vcpu->arch.host_fpexc); >>>>>>>>> +} >>>>>>>>> + >>>>>>>>> +/* If trap bits are reset then fp/simd registers are dirty */ >>>>>>>>> +static inline bool vcpu_vfp_isdirty(struct kvm_vcpu *vcpu) >>>>>>>>> +{ >>>>>>>>> + return !(vcpu->arch.hcptr & (HCPTR_TCP(10) | HCPTR_TCP(11))); >>>>>>>>> +} >>>>>>>>> +#else >>>>>>>>> +static inline void vcpu_trap_vfp_enable(struct kvm_vcpu *vcpu) >>>>>>>>> +{ >>>>>>>>> + vcpu->arch.hcptr = HCPTR_TTA; >>>>>>>> >>>>>>>> Is it correct not to trap VFP registers when the host kernel does not >>>>>>>> have CONFIG_VFPv3? I think this is a change in functionality compared >>>>>>>> to the current kernels is it not? >>>>>>> >>>>>>> With CPU_V7 VFPv3 gets selected, without it fp should be emulated, >>>>>>> with exceptions taken in guest kernel. I don't see a reason why >>>>>>> fp hcptr access should be enabled in that case. >>>>>>> >>>>>> >>>>>> If you have to guests with CONFIG_VFPV3 but your host doesn't have >>>>>> CONFIG_VFPV3, you will never context-switch the VFP registers between >>>>>> the two VMs, and mayhem will ensue. >>>>>> >>>>>> Unless I'm missing something very obvious? >>>> >>>> Did more testing on this enabling OABI_COMPAT and selecting >>>> NWFPE/FastFPE breaks the boot. So far can't find a way to boot host >>>> without VFP/VFPv3 enabled on ARMv7. CPU_V7 defaults to VFPv3 >>>> selection. I'm wondering if !VFPv3 path should be removed from >>>> the patches? >>>> >>> I think this is related to your particular choice of userspace. >> >> It appears like there are two soft float implementations. >> >> FastFPE - but that's missing arch/arm/fastfpe directory, the option >> can still be selected but nothing is built. >> >> And the Netwidner FPE arch/arm/nwfpe, that doesn't appear to be >> hooked into the kernel. The hook nwfpe_enter is not referenced >> anywhere. > > It is: > > arch/arm/nwfpe/entry.S: .globl nwfpe_enter > arch/arm/nwfpe/entry.S:nwfpe_enter: > arch/arm/nwfpe/fpmodule.c:extern void nwfpe_enter(void); > arch/arm/nwfpe/fpmodule.c: kern_fp_enter = nwfpe_enter; > >> I could make this change but have no way to bring the host up to >> test it. > > None of these are relevant - they are emulation for the FPA (Floating > Point Accelerator). Most of the time, nobody uses this but instead a > userspace softfloat implementation, which saves the trap to kernel space > for emulation. > > You can try Debian armel (as opposed to armhf, which mandates VFP) for > example, which is a softfloat-based distribution. I've been using armel debian but it appears some binaries have hard fp instructions (-mfloat-abi=hard,softfp). I have a simple rootfs now and it comes up cleanly on the host. I'll work on qemu now. Thanks for pointing out FPA. - Mario > > Thanks, > > M. >