From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-11.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4A90BC433E0 for ; Mon, 13 Jul 2020 15:40:11 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id CB71D20771 for ; Mon, 13 Jul 2020 15:40:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CB71D20771 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 174E94B260; Mon, 13 Jul 2020 11:40:10 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id YvDSm5aUKw5V; Mon, 13 Jul 2020 11:40:08 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id A8DEC4B26F; Mon, 13 Jul 2020 11:40:08 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id D40AB4B226 for ; Mon, 13 Jul 2020 11:40:07 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id fQHvxgkLBvuA for ; Mon, 13 Jul 2020 11:40:06 -0400 (EDT) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 10DDC4B1F7 for ; Mon, 13 Jul 2020 11:40:06 -0400 (EDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 45AA41FB; Mon, 13 Jul 2020 08:40:05 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8F55B3F7BB; Mon, 13 Jul 2020 08:40:04 -0700 (PDT) Date: Mon, 13 Jul 2020 16:40:02 +0100 From: Dave Martin To: Andrew Scull Subject: Re: [PATCH] arm64: kvm: Remove redundant KVM_ARM64_FP_HOST flag Message-ID: <20200713154002.GR10992@arm.com> References: <20200707145713.287710-1-ascull@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200707145713.287710-1-ascull@google.com> User-Agent: Mutt/1.5.23 (2014-03-12) Cc: maz@kernel.org, kernel-team@android.com, kvmarm@lists.cs.columbia.edu X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Tue, Jul 07, 2020 at 03:57:13PM +0100, Andrew Scull wrote: > The FPSIMD registers can be in one of three states: > (a) loaded with the user task's state > (b) loaded with the vcpu's state > (c) dirty with transient state > > KVM_ARM64_FP_HOST identifies the case (a). When loading the vcpu state, > this is used to decide whether to save the current FPSIMD registers to > the user task. > > However, at the point of loading the vcpu's FPSIMD state, it is known > that we are not in state (b). States (a) and (c) can be distinguished by > by checking the TIF_FOREIGN_FPSTATE bit, as was previously being done to > prepare the KVM_ARM64_FP_HOST flag but without the need for mirroring > the state. > > Signed-off-by: Andrew Scull Is your new series [1] intended to replace this, or do I need to look at both series now? Cheers ---Dave [1] Manage vcpu flags from the host https://lists.cs.columbia.edu/pipermail/kvmarm/2020-July/041531.html > --- > This is the result of trying to get my head around the FPSIMD handling. > If I've misunderstood something I'll be very happy to have it explained > to me :) > --- > arch/arm64/include/asm/kvm_host.h | 11 +++++---- > arch/arm64/kvm/fpsimd.c | 1 - > arch/arm64/kvm/hyp/include/hyp/switch.h | 30 +++++++++++++++++-------- > 3 files changed, 26 insertions(+), 16 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > index e0920df1d0c1..d3652745282d 100644 > --- a/arch/arm64/include/asm/kvm_host.h > +++ b/arch/arm64/include/asm/kvm_host.h > @@ -370,12 +370,11 @@ struct kvm_vcpu_arch { > /* vcpu_arch flags field values: */ > #define KVM_ARM64_DEBUG_DIRTY (1 << 0) > #define KVM_ARM64_FP_ENABLED (1 << 1) /* guest FP regs loaded */ > -#define KVM_ARM64_FP_HOST (1 << 2) /* host FP regs loaded */ > -#define KVM_ARM64_HOST_SVE_IN_USE (1 << 3) /* backup for host TIF_SVE */ > -#define KVM_ARM64_HOST_SVE_ENABLED (1 << 4) /* SVE enabled for EL0 */ > -#define KVM_ARM64_GUEST_HAS_SVE (1 << 5) /* SVE exposed to guest */ > -#define KVM_ARM64_VCPU_SVE_FINALIZED (1 << 6) /* SVE config completed */ > -#define KVM_ARM64_GUEST_HAS_PTRAUTH (1 << 7) /* PTRAUTH exposed to guest */ > +#define KVM_ARM64_HOST_SVE_IN_USE (1 << 2) /* backup for host TIF_SVE */ > +#define KVM_ARM64_HOST_SVE_ENABLED (1 << 3) /* SVE enabled for EL0 */ > +#define KVM_ARM64_GUEST_HAS_SVE (1 << 4) /* SVE exposed to guest */ > +#define KVM_ARM64_VCPU_SVE_FINALIZED (1 << 5) /* SVE config completed */ > +#define KVM_ARM64_GUEST_HAS_PTRAUTH (1 << 6) /* PTRAUTH exposed to guest */ > > #define vcpu_has_sve(vcpu) (system_supports_sve() && \ > ((vcpu)->arch.flags & KVM_ARM64_GUEST_HAS_SVE)) > diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c > index e329a36b2bee..4e9afeb31989 100644 > --- a/arch/arm64/kvm/fpsimd.c > +++ b/arch/arm64/kvm/fpsimd.c > @@ -65,7 +65,6 @@ void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu) > vcpu->arch.flags &= ~(KVM_ARM64_FP_ENABLED | > KVM_ARM64_HOST_SVE_IN_USE | > KVM_ARM64_HOST_SVE_ENABLED); > - vcpu->arch.flags |= KVM_ARM64_FP_HOST; > > if (test_thread_flag(TIF_SVE)) > vcpu->arch.flags |= KVM_ARM64_HOST_SVE_IN_USE; > diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h > index 8f622688fa64..beadf17f12a6 100644 > --- a/arch/arm64/kvm/hyp/include/hyp/switch.h > +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h > @@ -33,16 +33,24 @@ extern const char __hyp_panic_string[]; > static inline bool update_fp_enabled(struct kvm_vcpu *vcpu) > { > /* > - * When the system doesn't support FP/SIMD, we cannot rely on > - * the _TIF_FOREIGN_FPSTATE flag. However, we always inject an > - * abort on the very first access to FP and thus we should never > - * see KVM_ARM64_FP_ENABLED. For added safety, make sure we always > + * When entering the vcpu during a KVM_VCPU_RUN call before the vcpu > + * has used FPSIMD, FPSIMD is disabled for the vcpu and will trap when > + * it is first used. The FPSIMD state currently bound to the cpu is > + * that of the user task. > + * > + * After the vcpu has used FPSIMD, on subsequent entries into the vcpu > + * for the same KVM_VCPU_RUN call, the vcpu's FPSIMD state is bound to > + * the cpu. Therefore, if _TIF_FOREIGN_FPSTATE is set, we know the > + * FPSIMD registers no longer contain the vcpu's state. In this case we > + * must, once again, disable FPSIMD. > + * > + * When the system doesn't support FPSIMD, we cannot rely on the > + * _TIF_FOREIGN_FPSTATE flag. For added safety, make sure we always > * trap the accesses. > */ > if (!system_supports_fpsimd() || > vcpu->arch.host_thread_info->flags & _TIF_FOREIGN_FPSTATE) > - vcpu->arch.flags &= ~(KVM_ARM64_FP_ENABLED | > - KVM_ARM64_FP_HOST); > + vcpu->arch.flags &= ~KVM_ARM64_FP_ENABLED; > > return !!(vcpu->arch.flags & KVM_ARM64_FP_ENABLED); > } > @@ -245,7 +253,13 @@ static inline bool __hyp_handle_fpsimd(struct kvm_vcpu *vcpu) > > isb(); > > - if (vcpu->arch.flags & KVM_ARM64_FP_HOST) { > + /* > + * The trap means that the vcpu's FPSIMD state is not loaded. If > + * _TIF_FOREIGN_FPSTATE is set, the current state does not need to be > + * saved. Otherwise, the user task's state is currently loaded and > + * needs to be saved. > + */ > + if (!(vcpu->arch.host_thread_info->flags & _TIF_FOREIGN_FPSTATE)) { > /* > * In the SVE case, VHE is assumed: it is enforced by > * Kconfig and kvm_arch_init(). > @@ -260,8 +274,6 @@ static inline bool __hyp_handle_fpsimd(struct kvm_vcpu *vcpu) > } else { > __fpsimd_save_state(vcpu->arch.host_fpsimd_state); > } > - > - vcpu->arch.flags &= ~KVM_ARM64_FP_HOST; > } > > if (sve_guest) { > -- > 2.27.0.383.g050319c2ae-goog > > _______________________________________________ > kvmarm mailing list > kvmarm@lists.cs.columbia.edu > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm