From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932580AbcLZRsf (ORCPT ); Mon, 26 Dec 2016 12:48:35 -0500 Received: from outprodmail01.cc.columbia.edu ([128.59.72.39]:52028 "EHLO outprodmail01.cc.columbia.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755765AbcLZRs1 (ORCPT ); Mon, 26 Dec 2016 12:48:27 -0500 X-Greylist: delayed 1323 seconds by postgrey-1.27 at vger.kernel.org; Mon, 26 Dec 2016 12:46:20 EST From: Jintack Lim To: kvmarm@lists.cs.columbia.edu, christoffer.dall@linaro.org, marc.zyngier@arm.com Cc: pbonzini@redhat.com, rkrcmar@redhat.com, linux@armlinux.org.uk, catalin.marinas@arm.com, will.deacon@arm.com, andre.przywara@arm.com, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Jintack Lim Subject: [RFC 0/8] Provide the EL1 physical timer to the VM Date: Mon, 26 Dec 2016 12:11:58 -0500 Message-Id: <1482772326-29110-1-git-send-email-jintack@cs.columbia.edu> X-Mailer: git-send-email 1.9.1 X-No-Spam-Score: Local Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The ARM architecture defines the EL1 physical timer and the virtual timer, and it is reasonable for an OS to expect to be able to access both. However, the current KVM implementation does not provide the EL1 physical timer to VMs but terminates VMs on access to the timer. On VHE systems, this would be as simple as allowing full access to the EL1 physical timer to VMs because the KVM host does not use the EL1 physical timer. However, on non-VHE systems, the KVM host already uses the EL1 physical timer which prevents us from granting full access of the EL1 physical timer to VMs. This patchset enables VMs to use the EL1 physical timer through trap-and-emulate. The KVM host emulates each EL1 physical timer register access and sets up the background timer accordingly. When the background timer expires, the KVM host injects EL1 physical timer interrupts to the VM. Alternatively, it's also possible to allow VMs to access the EL1 physical timer without trapping. However, this requires somehow using the EL2 physical timer for the Linux host while running the VM instead of the EL1 physical timer. Right now I just implemented trap-and-emulate because this was straightforward to do, and I leave it to future work to determine if transferring the EL1 physical timer state to the EL2 timer provides any performance benefit. This feature will be useful for any OS that wishes to access the EL1 physical timer. Nested virtualization is one of those use cases. A nested hypervisor running inside a VM would think it has full access to the hardware and naturally tries to use the EL1 physical timer as Linux would do. Other nested hypervisors may try to use the EL2 physical timer as Xen would do, but supporting the EL2 physical timer to the VM is out of scope of this patchset. This patchset will make it easy to add the EL2 timer support in the future, though. Note, Linux VMs booting in EL1 will be unaffected by this patch set and will continue to use only the virtual timer and this patch set will therefore not introduce any performance degredation as a result of trap-and-emulate. Jintack Lim (8): KVM: arm/arm64: Abstract virtual timer context into separate structure KVM: arm/arm64: Decouple kvm timer functions from virtual timer KVM: arm/arm64: Add the EL1 physical timer context KVM: arm/arm64: Initialize the emulated EL1 physical timer KVM: arm64: Add the EL1 physical timer access handler KVM: arm/arm64: Update the physical timer interrupt level KVM: arm/arm64: Set up a background timer for the physical timer emulation KVM: arm/arm64: Emulate the EL1 phys timer register access arch/arm/kvm/arm.c | 3 +- arch/arm/kvm/reset.c | 9 +- arch/arm64/kvm/reset.c | 9 +- arch/arm64/kvm/sys_regs.c | 63 +++++++++++++ include/kvm/arm_arch_timer.h | 43 +++++---- virt/kvm/arm/arch_timer.c | 214 ++++++++++++++++++++++++++++++------------- virt/kvm/arm/hyp/timer-sr.c | 16 ++-- 7 files changed, 264 insertions(+), 93 deletions(-) -- 1.9.1