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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=ham 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 3401EC33CA2 for ; Fri, 10 Jan 2020 13:34:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ECB2C2077C for ; Fri, 10 Jan 2020 13:34:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578663272; bh=/50iOG87qgQkwYRzMG9xveGZkWaz2PiNIMaDoYAD8Ds=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=GVEx+X+NqGdAPkn7wK8PXsr9rXpHP9C8wIMC9coe1bOu32yxCIZpeVWuFmcB4Q6NS P7h7zdV3QgYnDRAMp/lJ7gg4aXZQud1GKGLicAJEo0Al6JGgy/V7BEQNOMqNPZebt7 g62+w36ff4TUbKJ7xCLN72vIJ+VMmORhURiBuP8E= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727866AbgAJNeb (ORCPT ); Fri, 10 Jan 2020 08:34:31 -0500 Received: from mail.kernel.org ([198.145.29.99]:45162 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727639AbgAJNea (ORCPT ); Fri, 10 Jan 2020 08:34:30 -0500 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 469B720721; Fri, 10 Jan 2020 13:34:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578663269; bh=/50iOG87qgQkwYRzMG9xveGZkWaz2PiNIMaDoYAD8Ds=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=jPGqPImOeO5JV/j2Xd1oChnLiUTRh+iDltUfx7iYdOz3l5g5s0427VBiYH7fR8P06 RxtHlWvLrgB9retjJltgtG+De1RmQ2LwTFK+2pFn4HYN63BjiNAgLgb3EiK6M8sBeZ dxpthEQIN8r/5oHYdNagNS7v1Gy8bcino15nqvT4= Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1ipuQl-0000tK-Ix; Fri, 10 Jan 2020 13:34:27 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Fri, 10 Jan 2020 13:34:27 +0000 From: Marc Zyngier To: Andrew Murray Cc: Catalin Marinas , Mark Rutland , will@kernel.org, Sudeep Holla , kvm@vger.kernel.org, kvmarm , linux-arm-kernel , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 09/18] arm64: KVM: enable conditional save/restore full SPE profiling buffer controls In-Reply-To: <20200110121211.GE42593@e119886-lin.cambridge.arm.com> References: <20191220143025.33853-1-andrew.murray@arm.com> <20191220143025.33853-10-andrew.murray@arm.com> <20191221141325.5a177343@why> <20200110105435.GC42593@e119886-lin.cambridge.arm.com> <2a9c9076588ef1dd36a6a365848cdfe7@kernel.org> <20200110121211.GE42593@e119886-lin.cambridge.arm.com> Message-ID: <485799f09fbf0c43c86c70b13cbcecd6@kernel.org> X-Sender: maz@kernel.org User-Agent: Roundcube Webmail/1.3.8 X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: andrew.murray@arm.com, Catalin.Marinas@arm.com, Mark.Rutland@arm.com, will@kernel.org, Sudeep.Holla@arm.com, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-01-10 12:12, Andrew Murray wrote: > On Fri, Jan 10, 2020 at 11:18:48AM +0000, Marc Zyngier wrote: >> On 2020-01-10 10:54, Andrew Murray wrote: >> > On Sat, Dec 21, 2019 at 02:13:25PM +0000, Marc Zyngier wrote: >> > > On Fri, 20 Dec 2019 14:30:16 +0000 >> > > Andrew Murray wrote: >> > > >> > > [somehow managed not to do a reply all, re-sending] >> > > >> > > > From: Sudeep Holla >> > > > >> > > > Now that we can save/restore the full SPE controls, we can enable it >> > > > if SPE is setup and ready to use in KVM. It's supported in KVM only if >> > > > all the CPUs in the system supports SPE. >> > > > >> > > > However to support heterogenous systems, we need to move the check if >> > > > host supports SPE and do a partial save/restore. >> > > >> > > No. Let's just not go down that path. For now, KVM on heterogeneous >> > > systems do not get SPE. If SPE has been enabled on a guest and a CPU >> > > comes up without SPE, this CPU should fail to boot (same as exposing a >> > > feature to userspace). >> > > >> > > > >> > > > Signed-off-by: Sudeep Holla >> > > > Signed-off-by: Andrew Murray >> > > > --- >> > > > arch/arm64/kvm/hyp/debug-sr.c | 33 ++++++++++++++++----------------- >> > > > include/kvm/arm_spe.h | 6 ++++++ >> > > > 2 files changed, 22 insertions(+), 17 deletions(-) >> > > > >> > > > diff --git a/arch/arm64/kvm/hyp/debug-sr.c b/arch/arm64/kvm/hyp/debug-sr.c >> > > > index 12429b212a3a..d8d857067e6d 100644 >> > > > --- a/arch/arm64/kvm/hyp/debug-sr.c >> > > > +++ b/arch/arm64/kvm/hyp/debug-sr.c >> > > > @@ -86,18 +86,13 @@ >> > > > } >> > > > >> > > > static void __hyp_text >> > > > -__debug_save_spe_nvhe(struct kvm_cpu_context *ctxt, bool full_ctxt) >> > > > +__debug_save_spe_context(struct kvm_cpu_context *ctxt, bool full_ctxt) >> > > > { >> > > > u64 reg; >> > > > >> > > > /* Clear pmscr in case of early return */ >> > > > ctxt->sys_regs[PMSCR_EL1] = 0; >> > > > >> > > > - /* SPE present on this CPU? */ >> > > > - if (!cpuid_feature_extract_unsigned_field(read_sysreg(id_aa64dfr0_el1), >> > > > - ID_AA64DFR0_PMSVER_SHIFT)) >> > > > - return; >> > > > - >> > > > /* Yes; is it owned by higher EL? */ >> > > > reg = read_sysreg_s(SYS_PMBIDR_EL1); >> > > > if (reg & BIT(SYS_PMBIDR_EL1_P_SHIFT)) >> > > > @@ -142,7 +137,7 @@ __debug_save_spe_nvhe(struct kvm_cpu_context *ctxt, bool full_ctxt) >> > > > } >> > > > >> > > > static void __hyp_text >> > > > -__debug_restore_spe_nvhe(struct kvm_cpu_context *ctxt, bool full_ctxt) >> > > > +__debug_restore_spe_context(struct kvm_cpu_context *ctxt, bool full_ctxt) >> > > > { >> > > > if (!ctxt->sys_regs[PMSCR_EL1]) >> > > > return; >> > > > @@ -210,11 +205,14 @@ void __hyp_text __debug_restore_guest_context(struct kvm_vcpu *vcpu) >> > > > struct kvm_guest_debug_arch *host_dbg; >> > > > struct kvm_guest_debug_arch *guest_dbg; >> > > > >> > > > + host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context); >> > > > + guest_ctxt = &vcpu->arch.ctxt; >> > > > + >> > > > + __debug_restore_spe_context(guest_ctxt, kvm_arm_spe_v1_ready(vcpu)); >> > > > + >> > > > if (!(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY)) >> > > > return; >> > > > >> > > > - host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context); >> > > > - guest_ctxt = &vcpu->arch.ctxt; >> > > > host_dbg = &vcpu->arch.host_debug_state.regs; >> > > > guest_dbg = kern_hyp_va(vcpu->arch.debug_ptr); >> > > > >> > > > @@ -232,8 +230,7 @@ void __hyp_text __debug_restore_host_context(struct kvm_vcpu *vcpu) >> > > > host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context); >> > > > guest_ctxt = &vcpu->arch.ctxt; >> > > > >> > > > - if (!has_vhe()) >> > > > - __debug_restore_spe_nvhe(host_ctxt, false); >> > > > + __debug_restore_spe_context(host_ctxt, kvm_arm_spe_v1_ready(vcpu)); >> > > >> > > So you now do an unconditional save/restore on the exit path for VHE >> > > as >> > > well? Even if the host isn't using the SPE HW? That's not acceptable >> > > as, in most cases, only the host /or/ the guest will use SPE. Here, >> > > you >> > > put a measurable overhead on each exit. >> > > >> > > If the host is not using SPE, then the restore/save should happen in >> > > vcpu_load/vcpu_put. Only if the host is using SPE should you do >> > > something in the run loop. Of course, this only applies to VHE and >> > > non-VHE must switch eagerly. >> > > >> > >> > On VHE where SPE is used in the guest only - we save/restore in >> > vcpu_load/put. >> >> Yes. >> >> > On VHE where SPE is used in the host only - we save/restore in the run >> > loop. >> >> Why? If only the host is using SPE, why should we do *anything at >> all*? > > Oh yeah of course, we trap them in this case. > > (Do I understand correctly that we don't/can't trap them for nVHE? - > and so > we should save/restore them for this use-case in nVHE) We can always trap. Otherwise we wouldn't be able to hide the feature from the guest. >> > On VHE where SPE is used in guest and host - we save/restore in the run >> > loop. >> > >> > As the guest can't trace EL2 it doesn't matter if we restore guest SPE >> > early >> > in the vcpu_load/put functions. (I assume it doesn't matter that we >> > restore >> > an EL0/EL1 profiling buffer address at this point and enable tracing >> > given >> > that there is nothing to trace until entering the guest). >> >> As long as you do it after the EL1 sysregs have need restored so that >> the >> SPE >> HW has a valid context, we should be fine. Don't restore it before >> that >> point >> though (you have no idea whether the SPE HW can do speculative memory >> accesses >> that would use the wrong page tables). > > Right, so don't enable tracing until SPE has a valid context. I > understand > that to mean at least the SPE buffer address registers (PMBPTR, > PMBLIMITR) > in the right context with respect to the E2PB bits (translation regime) > and having those tables mapped in (which I think relate to the > __activateX, > __sysreg_restore_guest_stateX type of calls in kvm_vcpu_run_X right?). The full MM context has to be in place before you can do anything. This means at least TTBR*_EL1, TCR_EL1 and co. But maybe this note in the SPE architecture document would allow us to relax things: "The Statistical Profiling Extension is always disabled if the owning Exception level is a lower Exception level than the current Exception level." So as long as you restore the guest state from EL2, SPE should be disabled. > I think that means we can restore the registers no earler than > vcpu_load/put > but we can't re-enable the tracing (PMSCR) until no earlier than just > before > __set_guest_arch_workaround_state. I think that applies to both VHE and > nVHE? I'm sorry, but I don't understand what you mean. M. -- Jazz is not dead. It just smells funny... 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Fri, 10 Jan 2020 13:34:27 +0000 MIME-Version: 1.0 Date: Fri, 10 Jan 2020 13:34:27 +0000 From: Marc Zyngier To: Andrew Murray Subject: Re: [PATCH v2 09/18] arm64: KVM: enable conditional save/restore full SPE profiling buffer controls In-Reply-To: <20200110121211.GE42593@e119886-lin.cambridge.arm.com> References: <20191220143025.33853-1-andrew.murray@arm.com> <20191220143025.33853-10-andrew.murray@arm.com> <20191221141325.5a177343@why> <20200110105435.GC42593@e119886-lin.cambridge.arm.com> <2a9c9076588ef1dd36a6a365848cdfe7@kernel.org> <20200110121211.GE42593@e119886-lin.cambridge.arm.com> Message-ID: <485799f09fbf0c43c86c70b13cbcecd6@kernel.org> X-Sender: maz@kernel.org User-Agent: Roundcube Webmail/1.3.8 X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: andrew.murray@arm.com, Catalin.Marinas@arm.com, Mark.Rutland@arm.com, will@kernel.org, Sudeep.Holla@arm.com, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Cc: kvm@vger.kernel.org, Catalin Marinas , linux-kernel@vger.kernel.org, Sudeep Holla , will@kernel.org, kvmarm , linux-arm-kernel 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-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On 2020-01-10 12:12, Andrew Murray wrote: > On Fri, Jan 10, 2020 at 11:18:48AM +0000, Marc Zyngier wrote: >> On 2020-01-10 10:54, Andrew Murray wrote: >> > On Sat, Dec 21, 2019 at 02:13:25PM +0000, Marc Zyngier wrote: >> > > On Fri, 20 Dec 2019 14:30:16 +0000 >> > > Andrew Murray wrote: >> > > >> > > [somehow managed not to do a reply all, re-sending] >> > > >> > > > From: Sudeep Holla >> > > > >> > > > Now that we can save/restore the full SPE controls, we can enable it >> > > > if SPE is setup and ready to use in KVM. It's supported in KVM only if >> > > > all the CPUs in the system supports SPE. >> > > > >> > > > However to support heterogenous systems, we need to move the check if >> > > > host supports SPE and do a partial save/restore. >> > > >> > > No. Let's just not go down that path. For now, KVM on heterogeneous >> > > systems do not get SPE. If SPE has been enabled on a guest and a CPU >> > > comes up without SPE, this CPU should fail to boot (same as exposing a >> > > feature to userspace). >> > > >> > > > >> > > > Signed-off-by: Sudeep Holla >> > > > Signed-off-by: Andrew Murray >> > > > --- >> > > > arch/arm64/kvm/hyp/debug-sr.c | 33 ++++++++++++++++----------------- >> > > > include/kvm/arm_spe.h | 6 ++++++ >> > > > 2 files changed, 22 insertions(+), 17 deletions(-) >> > > > >> > > > diff --git a/arch/arm64/kvm/hyp/debug-sr.c b/arch/arm64/kvm/hyp/debug-sr.c >> > > > index 12429b212a3a..d8d857067e6d 100644 >> > > > --- a/arch/arm64/kvm/hyp/debug-sr.c >> > > > +++ b/arch/arm64/kvm/hyp/debug-sr.c >> > > > @@ -86,18 +86,13 @@ >> > > > } >> > > > >> > > > static void __hyp_text >> > > > -__debug_save_spe_nvhe(struct kvm_cpu_context *ctxt, bool full_ctxt) >> > > > +__debug_save_spe_context(struct kvm_cpu_context *ctxt, bool full_ctxt) >> > > > { >> > > > u64 reg; >> > > > >> > > > /* Clear pmscr in case of early return */ >> > > > ctxt->sys_regs[PMSCR_EL1] = 0; >> > > > >> > > > - /* SPE present on this CPU? */ >> > > > - if (!cpuid_feature_extract_unsigned_field(read_sysreg(id_aa64dfr0_el1), >> > > > - ID_AA64DFR0_PMSVER_SHIFT)) >> > > > - return; >> > > > - >> > > > /* Yes; is it owned by higher EL? */ >> > > > reg = read_sysreg_s(SYS_PMBIDR_EL1); >> > > > if (reg & BIT(SYS_PMBIDR_EL1_P_SHIFT)) >> > > > @@ -142,7 +137,7 @@ __debug_save_spe_nvhe(struct kvm_cpu_context *ctxt, bool full_ctxt) >> > > > } >> > > > >> > > > static void __hyp_text >> > > > -__debug_restore_spe_nvhe(struct kvm_cpu_context *ctxt, bool full_ctxt) >> > > > +__debug_restore_spe_context(struct kvm_cpu_context *ctxt, bool full_ctxt) >> > > > { >> > > > if (!ctxt->sys_regs[PMSCR_EL1]) >> > > > return; >> > > > @@ -210,11 +205,14 @@ void __hyp_text __debug_restore_guest_context(struct kvm_vcpu *vcpu) >> > > > struct kvm_guest_debug_arch *host_dbg; >> > > > struct kvm_guest_debug_arch *guest_dbg; >> > > > >> > > > + host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context); >> > > > + guest_ctxt = &vcpu->arch.ctxt; >> > > > + >> > > > + __debug_restore_spe_context(guest_ctxt, kvm_arm_spe_v1_ready(vcpu)); >> > > > + >> > > > if (!(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY)) >> > > > return; >> > > > >> > > > - host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context); >> > > > - guest_ctxt = &vcpu->arch.ctxt; >> > > > host_dbg = &vcpu->arch.host_debug_state.regs; >> > > > guest_dbg = kern_hyp_va(vcpu->arch.debug_ptr); >> > > > >> > > > @@ -232,8 +230,7 @@ void __hyp_text __debug_restore_host_context(struct kvm_vcpu *vcpu) >> > > > host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context); >> > > > guest_ctxt = &vcpu->arch.ctxt; >> > > > >> > > > - if (!has_vhe()) >> > > > - __debug_restore_spe_nvhe(host_ctxt, false); >> > > > + __debug_restore_spe_context(host_ctxt, kvm_arm_spe_v1_ready(vcpu)); >> > > >> > > So you now do an unconditional save/restore on the exit path for VHE >> > > as >> > > well? Even if the host isn't using the SPE HW? That's not acceptable >> > > as, in most cases, only the host /or/ the guest will use SPE. Here, >> > > you >> > > put a measurable overhead on each exit. >> > > >> > > If the host is not using SPE, then the restore/save should happen in >> > > vcpu_load/vcpu_put. Only if the host is using SPE should you do >> > > something in the run loop. Of course, this only applies to VHE and >> > > non-VHE must switch eagerly. >> > > >> > >> > On VHE where SPE is used in the guest only - we save/restore in >> > vcpu_load/put. >> >> Yes. >> >> > On VHE where SPE is used in the host only - we save/restore in the run >> > loop. >> >> Why? If only the host is using SPE, why should we do *anything at >> all*? > > Oh yeah of course, we trap them in this case. > > (Do I understand correctly that we don't/can't trap them for nVHE? - > and so > we should save/restore them for this use-case in nVHE) We can always trap. Otherwise we wouldn't be able to hide the feature from the guest. >> > On VHE where SPE is used in guest and host - we save/restore in the run >> > loop. >> > >> > As the guest can't trace EL2 it doesn't matter if we restore guest SPE >> > early >> > in the vcpu_load/put functions. (I assume it doesn't matter that we >> > restore >> > an EL0/EL1 profiling buffer address at this point and enable tracing >> > given >> > that there is nothing to trace until entering the guest). >> >> As long as you do it after the EL1 sysregs have need restored so that >> the >> SPE >> HW has a valid context, we should be fine. Don't restore it before >> that >> point >> though (you have no idea whether the SPE HW can do speculative memory >> accesses >> that would use the wrong page tables). > > Right, so don't enable tracing until SPE has a valid context. I > understand > that to mean at least the SPE buffer address registers (PMBPTR, > PMBLIMITR) > in the right context with respect to the E2PB bits (translation regime) > and having those tables mapped in (which I think relate to the > __activateX, > __sysreg_restore_guest_stateX type of calls in kvm_vcpu_run_X right?). The full MM context has to be in place before you can do anything. This means at least TTBR*_EL1, TCR_EL1 and co. But maybe this note in the SPE architecture document would allow us to relax things: "The Statistical Profiling Extension is always disabled if the owning Exception level is a lower Exception level than the current Exception level." So as long as you restore the guest state from EL2, SPE should be disabled. > I think that means we can restore the registers no earler than > vcpu_load/put > but we can't re-enable the tracing (PMSCR) until no earlier than just > before > __set_guest_arch_workaround_state. I think that applies to both VHE and > nVHE? I'm sorry, but I don't understand what you mean. M. -- Jazz is not dead. It just smells funny... _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm 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=-7.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS 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 E51B1C33CA3 for ; Fri, 10 Jan 2020 13:34:34 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id B97122080D for ; Fri, 10 Jan 2020 13:34:34 +0000 (UTC) Authentication-Results: mail.kernel.org; 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Fri, 10 Jan 2020 13:34:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578663269; bh=/50iOG87qgQkwYRzMG9xveGZkWaz2PiNIMaDoYAD8Ds=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=jPGqPImOeO5JV/j2Xd1oChnLiUTRh+iDltUfx7iYdOz3l5g5s0427VBiYH7fR8P06 RxtHlWvLrgB9retjJltgtG+De1RmQ2LwTFK+2pFn4HYN63BjiNAgLgb3EiK6M8sBeZ dxpthEQIN8r/5oHYdNagNS7v1Gy8bcino15nqvT4= Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1ipuQl-0000tK-Ix; Fri, 10 Jan 2020 13:34:27 +0000 MIME-Version: 1.0 Date: Fri, 10 Jan 2020 13:34:27 +0000 From: Marc Zyngier To: Andrew Murray Subject: Re: [PATCH v2 09/18] arm64: KVM: enable conditional save/restore full SPE profiling buffer controls In-Reply-To: <20200110121211.GE42593@e119886-lin.cambridge.arm.com> References: <20191220143025.33853-1-andrew.murray@arm.com> <20191220143025.33853-10-andrew.murray@arm.com> <20191221141325.5a177343@why> <20200110105435.GC42593@e119886-lin.cambridge.arm.com> <2a9c9076588ef1dd36a6a365848cdfe7@kernel.org> <20200110121211.GE42593@e119886-lin.cambridge.arm.com> Message-ID: <485799f09fbf0c43c86c70b13cbcecd6@kernel.org> X-Sender: maz@kernel.org User-Agent: Roundcube Webmail/1.3.8 X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: andrew.murray@arm.com, Catalin.Marinas@arm.com, Mark.Rutland@arm.com, will@kernel.org, Sudeep.Holla@arm.com, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200110_053430_179640_3C182899 X-CRM114-Status: GOOD ( 33.42 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , kvm@vger.kernel.org, Catalin Marinas , linux-kernel@vger.kernel.org, Sudeep Holla , will@kernel.org, kvmarm , linux-arm-kernel Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2020-01-10 12:12, Andrew Murray wrote: > On Fri, Jan 10, 2020 at 11:18:48AM +0000, Marc Zyngier wrote: >> On 2020-01-10 10:54, Andrew Murray wrote: >> > On Sat, Dec 21, 2019 at 02:13:25PM +0000, Marc Zyngier wrote: >> > > On Fri, 20 Dec 2019 14:30:16 +0000 >> > > Andrew Murray wrote: >> > > >> > > [somehow managed not to do a reply all, re-sending] >> > > >> > > > From: Sudeep Holla >> > > > >> > > > Now that we can save/restore the full SPE controls, we can enable it >> > > > if SPE is setup and ready to use in KVM. It's supported in KVM only if >> > > > all the CPUs in the system supports SPE. >> > > > >> > > > However to support heterogenous systems, we need to move the check if >> > > > host supports SPE and do a partial save/restore. >> > > >> > > No. Let's just not go down that path. For now, KVM on heterogeneous >> > > systems do not get SPE. If SPE has been enabled on a guest and a CPU >> > > comes up without SPE, this CPU should fail to boot (same as exposing a >> > > feature to userspace). >> > > >> > > > >> > > > Signed-off-by: Sudeep Holla >> > > > Signed-off-by: Andrew Murray >> > > > --- >> > > > arch/arm64/kvm/hyp/debug-sr.c | 33 ++++++++++++++++----------------- >> > > > include/kvm/arm_spe.h | 6 ++++++ >> > > > 2 files changed, 22 insertions(+), 17 deletions(-) >> > > > >> > > > diff --git a/arch/arm64/kvm/hyp/debug-sr.c b/arch/arm64/kvm/hyp/debug-sr.c >> > > > index 12429b212a3a..d8d857067e6d 100644 >> > > > --- a/arch/arm64/kvm/hyp/debug-sr.c >> > > > +++ b/arch/arm64/kvm/hyp/debug-sr.c >> > > > @@ -86,18 +86,13 @@ >> > > > } >> > > > >> > > > static void __hyp_text >> > > > -__debug_save_spe_nvhe(struct kvm_cpu_context *ctxt, bool full_ctxt) >> > > > +__debug_save_spe_context(struct kvm_cpu_context *ctxt, bool full_ctxt) >> > > > { >> > > > u64 reg; >> > > > >> > > > /* Clear pmscr in case of early return */ >> > > > ctxt->sys_regs[PMSCR_EL1] = 0; >> > > > >> > > > - /* SPE present on this CPU? */ >> > > > - if (!cpuid_feature_extract_unsigned_field(read_sysreg(id_aa64dfr0_el1), >> > > > - ID_AA64DFR0_PMSVER_SHIFT)) >> > > > - return; >> > > > - >> > > > /* Yes; is it owned by higher EL? */ >> > > > reg = read_sysreg_s(SYS_PMBIDR_EL1); >> > > > if (reg & BIT(SYS_PMBIDR_EL1_P_SHIFT)) >> > > > @@ -142,7 +137,7 @@ __debug_save_spe_nvhe(struct kvm_cpu_context *ctxt, bool full_ctxt) >> > > > } >> > > > >> > > > static void __hyp_text >> > > > -__debug_restore_spe_nvhe(struct kvm_cpu_context *ctxt, bool full_ctxt) >> > > > +__debug_restore_spe_context(struct kvm_cpu_context *ctxt, bool full_ctxt) >> > > > { >> > > > if (!ctxt->sys_regs[PMSCR_EL1]) >> > > > return; >> > > > @@ -210,11 +205,14 @@ void __hyp_text __debug_restore_guest_context(struct kvm_vcpu *vcpu) >> > > > struct kvm_guest_debug_arch *host_dbg; >> > > > struct kvm_guest_debug_arch *guest_dbg; >> > > > >> > > > + host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context); >> > > > + guest_ctxt = &vcpu->arch.ctxt; >> > > > + >> > > > + __debug_restore_spe_context(guest_ctxt, kvm_arm_spe_v1_ready(vcpu)); >> > > > + >> > > > if (!(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY)) >> > > > return; >> > > > >> > > > - host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context); >> > > > - guest_ctxt = &vcpu->arch.ctxt; >> > > > host_dbg = &vcpu->arch.host_debug_state.regs; >> > > > guest_dbg = kern_hyp_va(vcpu->arch.debug_ptr); >> > > > >> > > > @@ -232,8 +230,7 @@ void __hyp_text __debug_restore_host_context(struct kvm_vcpu *vcpu) >> > > > host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context); >> > > > guest_ctxt = &vcpu->arch.ctxt; >> > > > >> > > > - if (!has_vhe()) >> > > > - __debug_restore_spe_nvhe(host_ctxt, false); >> > > > + __debug_restore_spe_context(host_ctxt, kvm_arm_spe_v1_ready(vcpu)); >> > > >> > > So you now do an unconditional save/restore on the exit path for VHE >> > > as >> > > well? Even if the host isn't using the SPE HW? That's not acceptable >> > > as, in most cases, only the host /or/ the guest will use SPE. Here, >> > > you >> > > put a measurable overhead on each exit. >> > > >> > > If the host is not using SPE, then the restore/save should happen in >> > > vcpu_load/vcpu_put. Only if the host is using SPE should you do >> > > something in the run loop. Of course, this only applies to VHE and >> > > non-VHE must switch eagerly. >> > > >> > >> > On VHE where SPE is used in the guest only - we save/restore in >> > vcpu_load/put. >> >> Yes. >> >> > On VHE where SPE is used in the host only - we save/restore in the run >> > loop. >> >> Why? If only the host is using SPE, why should we do *anything at >> all*? > > Oh yeah of course, we trap them in this case. > > (Do I understand correctly that we don't/can't trap them for nVHE? - > and so > we should save/restore them for this use-case in nVHE) We can always trap. Otherwise we wouldn't be able to hide the feature from the guest. >> > On VHE where SPE is used in guest and host - we save/restore in the run >> > loop. >> > >> > As the guest can't trace EL2 it doesn't matter if we restore guest SPE >> > early >> > in the vcpu_load/put functions. (I assume it doesn't matter that we >> > restore >> > an EL0/EL1 profiling buffer address at this point and enable tracing >> > given >> > that there is nothing to trace until entering the guest). >> >> As long as you do it after the EL1 sysregs have need restored so that >> the >> SPE >> HW has a valid context, we should be fine. Don't restore it before >> that >> point >> though (you have no idea whether the SPE HW can do speculative memory >> accesses >> that would use the wrong page tables). > > Right, so don't enable tracing until SPE has a valid context. I > understand > that to mean at least the SPE buffer address registers (PMBPTR, > PMBLIMITR) > in the right context with respect to the E2PB bits (translation regime) > and having those tables mapped in (which I think relate to the > __activateX, > __sysreg_restore_guest_stateX type of calls in kvm_vcpu_run_X right?). The full MM context has to be in place before you can do anything. This means at least TTBR*_EL1, TCR_EL1 and co. But maybe this note in the SPE architecture document would allow us to relax things: "The Statistical Profiling Extension is always disabled if the owning Exception level is a lower Exception level than the current Exception level." So as long as you restore the guest state from EL2, SPE should be disabled. > I think that means we can restore the registers no earler than > vcpu_load/put > but we can't re-enable the tracing (PMSCR) until no earlier than just > before > __set_guest_arch_workaround_state. I think that applies to both VHE and > nVHE? I'm sorry, but I don't understand what you mean. M. -- Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel