From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoffer Dall Subject: Re: [PATCHv2 09/12] arm64/kvm: preserve host HCR_EL2 value Date: Mon, 9 Apr 2018 21:03:24 +0200 Message-ID: <20180409190324.GG10904@cbox> References: <20171127163806.31435-1-mark.rutland@arm.com> <20171127163806.31435-10-mark.rutland@arm.com> <20180206123915.GA21802@cbox> <20180409145709.dneotb6xaznw44c4@lakrids.cambridge.arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20180409145709.dneotb6xaznw44c4@lakrids.cambridge.arm.com> Sender: linux-kernel-owner@vger.kernel.org To: Mark Rutland Cc: linux-arm-kernel@lists.infradead.org, arnd@arndb.de, catalin.marinas@arm.com, kvmarm@lists.cs.columbia.edu, linux-arch@vger.kernel.org, marc.zyngier@arm.com, suzuki.poulose@arm.com, will.deacon@arm.com, yao.qi@arm.com, kernel-hardening@lists.openwall.com, linux-kernel@vger.kernel.org, awallis@codeaurora.org List-Id: linux-arch.vger.kernel.org On Mon, Apr 09, 2018 at 03:57:09PM +0100, Mark Rutland wrote: > On Tue, Feb 06, 2018 at 01:39:15PM +0100, Christoffer Dall wrote: > > On Mon, Nov 27, 2017 at 04:38:03PM +0000, Mark Rutland wrote: > > > diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c > > > index 525c01f48867..2205f0be3ced 100644 > > > --- a/arch/arm64/kvm/hyp/switch.c > > > +++ b/arch/arm64/kvm/hyp/switch.c > > > @@ -71,6 +71,8 @@ static void __hyp_text __activate_traps(struct kvm_vcpu *vcpu) > > > { > > > u64 val; > > > > > > + vcpu->arch.host_hcr_el2 = read_sysreg(hcr_el2); > > > + > > > > Looking back at this, it seems excessive to switch this at every > > round-trip. I think it should be possible to have this as a single > > global (or per-CPU) variable that gets restored directly when returning > > from the VM. > > I suspect this needs to be per-cpu, to account for heterogeneous > systems. > > I guess if we move hcr_el2 into kvm_cpu_context, that gives us a > per-vcpu copy for guests, and a per-cpu copy for the host (in the global > kvm_host_cpu_state). > > I'll have a look at how gnarly that turns out. I'm not sure how we can > initialise that sanely for the !VHE case to match whatever el2_setup > did. There's no harm in jumping down to EL2 to read a register during the initialization phase. All it requires is an annotation of the callee function, and a kvm_call_hyp(), and it's actually quite fast unless you start saving/restoring a bunch of additional system registers. See how we call __kvm_set_tpidr_el2() for example. Thanks, -Christoffer From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f67.google.com ([74.125.82.67]:55365 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751662AbeDITD1 (ORCPT ); Mon, 9 Apr 2018 15:03:27 -0400 Received: by mail-wm0-f67.google.com with SMTP id b127so21376307wmf.5 for ; Mon, 09 Apr 2018 12:03:26 -0700 (PDT) Date: Mon, 9 Apr 2018 21:03:24 +0200 From: Christoffer Dall Subject: Re: [PATCHv2 09/12] arm64/kvm: preserve host HCR_EL2 value Message-ID: <20180409190324.GG10904@cbox> References: <20171127163806.31435-1-mark.rutland@arm.com> <20171127163806.31435-10-mark.rutland@arm.com> <20180206123915.GA21802@cbox> <20180409145709.dneotb6xaznw44c4@lakrids.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180409145709.dneotb6xaznw44c4@lakrids.cambridge.arm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Mark Rutland Cc: linux-arm-kernel@lists.infradead.org, arnd@arndb.de, catalin.marinas@arm.com, kvmarm@lists.cs.columbia.edu, linux-arch@vger.kernel.org, marc.zyngier@arm.com, suzuki.poulose@arm.com, will.deacon@arm.com, yao.qi@arm.com, kernel-hardening@lists.openwall.com, linux-kernel@vger.kernel.org, awallis@codeaurora.org Message-ID: <20180409190324.yVZnu_pcx4RRZoYxmk6WjotfTDVp-EN0fWcp01MOE4U@z> On Mon, Apr 09, 2018 at 03:57:09PM +0100, Mark Rutland wrote: > On Tue, Feb 06, 2018 at 01:39:15PM +0100, Christoffer Dall wrote: > > On Mon, Nov 27, 2017 at 04:38:03PM +0000, Mark Rutland wrote: > > > diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c > > > index 525c01f48867..2205f0be3ced 100644 > > > --- a/arch/arm64/kvm/hyp/switch.c > > > +++ b/arch/arm64/kvm/hyp/switch.c > > > @@ -71,6 +71,8 @@ static void __hyp_text __activate_traps(struct kvm_vcpu *vcpu) > > > { > > > u64 val; > > > > > > + vcpu->arch.host_hcr_el2 = read_sysreg(hcr_el2); > > > + > > > > Looking back at this, it seems excessive to switch this at every > > round-trip. I think it should be possible to have this as a single > > global (or per-CPU) variable that gets restored directly when returning > > from the VM. > > I suspect this needs to be per-cpu, to account for heterogeneous > systems. > > I guess if we move hcr_el2 into kvm_cpu_context, that gives us a > per-vcpu copy for guests, and a per-cpu copy for the host (in the global > kvm_host_cpu_state). > > I'll have a look at how gnarly that turns out. I'm not sure how we can > initialise that sanely for the !VHE case to match whatever el2_setup > did. There's no harm in jumping down to EL2 to read a register during the initialization phase. All it requires is an annotation of the callee function, and a kvm_call_hyp(), and it's actually quite fast unless you start saving/restoring a bunch of additional system registers. See how we call __kvm_set_tpidr_el2() for example. Thanks, -Christoffer