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=-5.5 required=3.0 tests=MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 57D84C433FF for ; Mon, 5 Aug 2019 16:29:05 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id D8CA12173B for ; Mon, 5 Aug 2019 16:29:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D8CA12173B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 571FB4A4E9; Mon, 5 Aug 2019 12:29:04 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id KhZ3wuTGdgcL; Mon, 5 Aug 2019 12:29:03 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 1AD2B4A51D; Mon, 5 Aug 2019 12:29:03 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id EBC524A4E9 for ; Mon, 5 Aug 2019 12:29:01 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id GTSgNysJHhLI for ; Mon, 5 Aug 2019 12:29:00 -0400 (EDT) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by mm01.cs.columbia.edu (Postfix) with ESMTP id C50314A4C0 for ; Mon, 5 Aug 2019 12:29:00 -0400 (EDT) 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 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-Language: en-US Cc: kvm@vger.kernel.org, Catalin Marinas , linux-doc@vger.kernel.org, Russell King , linux-kernel@vger.kernel.org, Paolo Bonzini , Will Deacon , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org 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-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu 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... _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm