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=-5.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 1C2E5C433FF for ; Mon, 5 Aug 2019 16:29:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E3B1E2086D for ; Mon, 5 Aug 2019 16:29:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1565022552; bh=dCJz3UpwG2J4Jywk6aEw0EeYoqu+jo/GEAS5b6ZqMXU=; h=Subject:To:Cc:References:From:Date:In-Reply-To:List-ID:From; b=1uLnlKbImmK6U70tXZLCZRuwCSv790Q7r1bQvI3Q/P+AYULWxhyNozPFFTFI1lntA rA1blBx2UvVC1DfUVD2zbJLLfAM8apTMUeShCs5cze3ZIv9qQPWZZCCGpNfUbUcYWx Tdnkgf/Bx4bwURkq6Z+r7NjZzL6ym6zWzPBuO2no= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730146AbfHEQ3K (ORCPT ); Mon, 5 Aug 2019 12:29:10 -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: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@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...