From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-6.0 required=5.0 tests=MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id D6EBD7E285 for ; Mon, 5 Aug 2019 16:29:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729856AbfHEQ3J (ORCPT ); Mon, 5 Aug 2019 12:29:09 -0400 Received: from foss.arm.com ([217.140.110.172]:51590 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729835AbfHEQ3B (ORCPT ); Mon, 5 Aug 2019 12:29:01 -0400 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 5058A344; Mon, 5 Aug 2019 09:29:00 -0700 (PDT) Received: from [10.1.197.61] (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 96E5D3F694; Mon, 5 Aug 2019 09:28:58 -0700 (PDT) Subject: Re: [PATCH 6/9] KVM: arm64: Provide a PV_TIME device to user space To: Steven Price Cc: kvm@vger.kernel.org, =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Catalin Marinas , Suzuki K Pouloze , linux-doc@vger.kernel.org, Russell King , linux-kernel@vger.kernel.org, James Morse , linux-arm-kernel@lists.infradead.org, Paolo Bonzini , Will Deacon , kvmarm@lists.cs.columbia.edu, Julien Thierry References: <20190802145017.42543-1-steven.price@arm.com> <20190802145017.42543-7-steven.price@arm.com> <20190803135113.6cdf500c@why> <1a7d5be6-184b-0c78-61a3-b01730cb5df9@arm.com> From: Marc Zyngier Organization: Approximate Message-ID: Date: Mon, 5 Aug 2019 17:28:57 +0100 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <1a7d5be6-184b-0c78-61a3-b01730cb5df9@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On 05/08/2019 17:10, Steven Price wrote: > On 03/08/2019 13:51, Marc Zyngier wrote: >> On Fri, 2 Aug 2019 15:50:14 +0100 >> Steven Price wrote: >> >>> Allow user space to inform the KVM host where in the physical memory >>> map the paravirtualized time structures should be located. >>> >>> A device is created which provides the base address of an array of >>> Stolen Time (ST) structures, one for each VCPU. There must be (64 * >>> total number of VCPUs) bytes of memory available at this location. >>> >>> The address is given in terms of the physical address visible to >>> the guest and must be 64 byte aligned. The memory should be marked as >>> reserved to the guest to stop it allocating it for other purposes. >> >> Why? You seem to be allocating the memory from the kernel, so as far as >> the guest is concerned, this isn't generally usable memory. > > I obviously didn't word it very well - that's what I meant. The "memory" > that represents the stolen time structure shouldn't be shown to the > guest as normal memory, but "reserved" for the purpose of stolen time. > > To be honest it looks like I forgot to rewrite this commit message - > which 64 byte alignment is all that the guest can rely on (because each > vCPU has it's own structure), the actual array of structures needs to be > page aligned to ensure we can safely map it into the guest. > >>> >>> Signed-off-by: Steven Price >>> --- >>> arch/arm64/include/asm/kvm_mmu.h | 2 + >>> arch/arm64/include/uapi/asm/kvm.h | 6 + >>> arch/arm64/kvm/Makefile | 1 + >>> include/uapi/linux/kvm.h | 2 + >>> virt/kvm/arm/mmu.c | 44 +++++++ >>> virt/kvm/arm/pvtime.c | 190 ++++++++++++++++++++++++++++++ >>> 6 files changed, 245 insertions(+) >>> create mode 100644 virt/kvm/arm/pvtime.c [...] >>> +static int kvm_arm_pvtime_set_attr(struct kvm_device *dev, >>> + struct kvm_device_attr *attr) >>> +{ >>> + struct kvm_arch_pvtime *pvtime = &dev->kvm->arch.pvtime; >>> + u64 __user *user = (u64 __user *)attr->addr; >>> + u64 paddr; >>> + int ret; >>> + >>> + switch (attr->group) { >>> + case KVM_DEV_ARM_PV_TIME_PADDR: >>> + if (get_user(paddr, user)) >>> + return -EFAULT; >>> + if (paddr & 63) >>> + return -EINVAL; >> >> You should check whether the device fits into the IPA space for this >> guest, and whether it overlaps with anything else. > > pvtime_map_pages() should fail in the case of overlap. That seems > sufficient to me - do you think we need something stronger? Definitely. stage2_set_pte() won't fail for a non-IO overlapping mapping, and will just treat it as guest memory. If this overlaps with a memslot, we'll never be able to fault that page in, ending up with interesting memory corruption... :-/ That's one of the reasons why I think option (2) in your earlier email is an interesting one, as it sidesteps a whole lot of ugly and hard to test corner cases. Thanks, M. -- Jazz is not dead, it just smells funny...