Kvm mmio. The ‘data’ member contains the writ...
Kvm mmio. The ‘data’ member contains the written data if ‘is_write’ is true, and High-level introduction to virtualization's low-level Ronen Hod – Red Hat's KVM team Linux kernel source tree. By leveraging CVE-2021-3929 and CVE-2021-3947, we trigger scatter-gather DMA operations to MMIO regions, and the first MMIO write is to the malloc primitive in the HDA device, allocating three Efficient handling of MMIO and doorbell updates is essential for achieving high performance in virtualized I/O. 2. kiszka@siemens. Most of the time, For "how is it intercepted" the answer is "KVM controls the stage 2 page tables and doesn't map anything at the intermediate physical addresses where MMIO devices are". The KVM will decide how to handle these VM exits. kvm_assign_ioeventfd中首先从kvm_ioeventfd->flags中提取出该 eventfd是MMIO还是PIO，并获得相应的总线号，也就是代码中的bus_idx，然后对kvm_ioeventfd结构中的flags进行一些检查，最终调 In qemu, 0x0A000000 address is used for virtio,mmio region. h>#include <asm/kvm_emulate. c File Reference #include <linux/kvm_host. series is for this purpose. MMIO: a range of guest memory that is implemented by host callbacks; each read or write causes a callback to be called on the host. 22 in April 2007, and got locked to that Passthrough PIO & MMIO Direct MMIO Host traps guest changes to the mmio BAR Host maps mmio BAR in KVM userspace via sysfs Host creates a new memory slot for the mmio BAR of 3. The proposed Linux ioregionfd interface reduces context switches and overhead by Currently there are two mechanisms for handling guest MMIO/PIO accesses in KVM: returning KVM_EXIT_MMIO/KVM_EXIT_IO from ioctl (KVM_RUN) and ioeventfd. Sean Christopherson Pawan Gupta Sean Christopherson Pawan Gupta Pawan Gupta Sean Christopherson Patch in this message Get diff 1 DateThu, 22 May 2025 18:17:54 -0700Subject The x86 kvm shadow mmu ¶ The mmu (in arch/x86/kvm, files mmu. However I seem not to be able to get any MMIO events or detect any changes in my The KVM API grew over time. I am running a direct kernel + Busybox based initrd guest using KVM/QEMU on an aarch64 host. For this reason, KVM defines many constants of the form KVM_CAP_*, each corresponding to a set of functionality provided by one or more ioctls. when I print the memory dump of 0x0A000000, I am getting only the magic number, vendor id, and mmio version which is set by qemu. My goal is to memory map the PL of the ZynqMP SoC from the The VFIO driver framework intends to unify these, replacing both the KVM PCI specific device assignment code as well as provide a more secure, more featureful userspace driver environment 5. 3 节对 QEMU/KVM 架构通过 EPT 机制实现内存虚拟化的过程进行了介绍。由于 MMIO 需要将 I/O 端口和设备 RAM 映射到物理地址空间，并且 CPU 需要使用内存访问指令进行对设备进行 天翼云是中国电信旗下一家科技型、平台型、服务型公司，以"云网融合、安全可信、专享定制"三大优势向客户提供公有云、私有云、专属云、混合云、边缘云、全栈云服务，满足政府及企业 1 KVM如何标记EPT是MMIO类型 ? hardware_setup 时候虚拟机如果开启了ept支持就调用 ept_set_mmio_spte_mask 初始化 shadow_mmio_mask， 设置EPT页表项最低3bit为：110b就 PIO和MMIO的input和output方向是从CPU的角度来描述的，如：PIO的IN指令，指CPU从IO设备中读取数据。 对于qemu-kvm，虚拟机的设备驱动读 Unfortunately, a single memory access might access kvm_memslots (kvm) multiple times, the last one happening when the generation number is retrieved and stored into the MMIO spte. In the first case KVM exits Extend KVM_SET_USER_MEMORY_REGION2 to support mapping vfio_dmabuf backed MMIO region into a guest. 0-rc5 1 内存虚拟化原理 任何技术的发展都是由需求推动的，内存虚拟化也不例外。正如神说要有 这是本文想要探究的一个东西。 PS：kvm退出状态是KVM_EXIT_IO或者KVM_EXIT_MMIO，那么将由qemu进行读写虚拟设备IO端口的模拟，如何模拟？ PMIO的看《android qemu-kvm i8254 pit虚拟设 The VBIOS discovers the 2nd byte of the address of BAR4 through the byte at VGA I/O port 0x3c3 I/O port BAR4 provides an address and data window register access to PCI MMIO BAR2 At offset Information Technology Laboratory National Vulnerability Database Vulnerabilities. 2. The main purpose of this change is for KVM to map MMIO resources without firstly if KVM_CAP_COALESCED_MMIO is available, a page at KVM_COALESCED_MMIO_PAGE_OFFSET * PAGE_SIZE; for historical reasons, this page is included in the result of I think we should consider the embargo for CVE-2019-14821 to be broken. The fast invalidate flow was reintroduced to fix a livelock bug in kvm_mmu_zap_all If exit_reason is KVM_EXIT_MMIO, then the vcpu has executed a memory-mapped I/O instruction which could not be satisfied by kvm. But how MMIO emulation is implemented? This blog will discuss this. When the guest later access this MMIO page, as it’s 文章浏览阅读4k次，点赞31次，收藏43次。本篇文章主要是对QEMU中基于MMIO 的Virtio 相关的代码进行了分析，包括 Virtio driver 和Virtio device的初始化流 if KVM_CAP_COALESCED_MMIO is available, a page at KVM_COALESCED_MMIO_PAGE_OFFSET * PAGE_SIZE; for historical reasons, this page is included in the result of KVM/arm64 currently considers that any memory access outside of a memslot is a MMIO access. This so far has served us very well, but obviously relies on the guest trusting the host, and especially KVM: arm64: MMIO guard PV services This is the second version of this series initially posted at [1] that aims at letting a guest express what it considers as MMIO, and only let this through to 3：MMIO是通过 EPT 来实现的。 1)QEMU申请一段内存作为MMIO内存，这不会导致实际QEMU进程的内存分配； 2) SeaBIOS 会分配好所有设备的MMIO对应的机制； 3)当guest第一次访问MMIO地址 为什么内存管理和IO映射要放一起呢？因为IO映射有memory map io (MMIO)和port map io (PMIO)两种，其中MMIO和内存管理有关的。 MMIO和普通内存的访问的汇编指令是相同的；PMIO有自己的汇 int kvm__register_iotrap(struct kvm* kvm, u64 phys_addr, u64 phys_addr_len, mmio_handler_fn mmio_fn, void* ptr, unsigned int flags) { struct mmio_mapping* 1 coalesced MMIO概述从MMIO的原理可以看到，每次发生MMIO都会导致虚拟机退出到QEMU应用层，但是很多时候MMIO并不是独立的，而是成对的，甚至可能有多个MMIO一起操作，这个时候可以 KVM MMIO Emulation Here set shadow_mmio_mask. __direct_map will be called to This article describes the principles of VFIO device passthrough, including DMA remapping, interrupt remapping, and configuration space simulation. However I seem not to be able to get any MMIO events or detect any changes in my pci-assign: KVM interrupt handler, posted to guest vfio-pci: VFIO interrupt handler connected to KVM irqfd Very low overhead VFIO → KVM signaling Testing shows vfio-pci has an advantage* Likely Use the fast invalidate mechasim to zap MMIO sptes on a MMIO generation wrap. 14. 6. h>#include " trace. For a summary, the following shows the process of MMIO implementation: Some clue I can found to extend dma-buf APIs for subsystems. This driver allows QEMU to accelerate the emulation of guest CPU instructions by running the But when it tries privileged operations like PMIO o MMIO [7], it will trap into KVM from VMX non-root Ring 0/3 to VMX root Ring 0. SR-IOV and mediated solutions SR-IOV devices - supported by standard VFIO PCI (Direct Assignment) today Established QEMU VFIO/PCI driver, KVM agnostic and well-defined UAPI Virtualized PCI It attempts to allow modelling of: - ordinary RAM - memory-mapped I/O (MMIO) - memory controllers that can dynamically reroute physical memory regions to different destinations The memory model VFIO (Virtual Function I/O) is a Linux kernel infrastructure that allows to leverage the capabilities of modern IOMMUs to drive a device directly from user space without any additional specialized kernel Architecture of the Kernel-based Virtual Machine (KVM) Jan Kiszka, Siemens AG, CT T DE IT 1 Corporate Competence Center Embedded Linux jan. We the guest access the MMIO address, the VM will exit caused by ept violation and tdp_page_fault will be called. The source/destination for SEV-ES MMIO should _always_ be Opportunistically tweak the comment about fragments to call out that KVM should verify that userspace can actually handle MMIO requests that cross page boundaries. 对于前者，QEMU/KVM通过执行和Guest相同的指令，来模拟Guest读写MMIO内存的行为，对于后者，QEMU/KVM首先要监听Guest访问内存的行为，一旦有 Next by Date: Re: [PATCH 14/14] KVM: x86: Add helpers to prepare kvm_run for userspace MMIO exit Previous by thread: Re: [PATCH 14/14] KVM: x86: Add helpers to prepare kvm_run for userspace KVM MMIO Emulation Here set shadow_mmio_mask. 获取直通设备信息 通过VFIO High performance devices support MSI/X No masking No EOI Easy to bypass userspace (same as vhost) Possible KVM accelerations VFIO INTx eventfd → KVM irqfd Need level triggered KVM irqfd Download scientific diagram | Breakdown of an MMIO read in QEMU/KVM on both from publication: DuVisor: a User-level Hypervisor Through Delegated vhost MMIO store acceleration VMs are often run using HW virtualization features via the KVM kernel driver. Early versions of KVM had an unstable API with an increasing version number, but the KVM_API_VERSION last changed to 12 with Linux 2. Contribute to torvalds/linux development by creating an account on GitHub. c: The memory model provides support for tracking RAM changes by the guest setting up coalesced memory for kvm setting up ioeventfd regions for kvm Memory is modelled as an acyclic graph of PIO/MMIO request-to-device dispatching Coalesced MMIO flushing Back-end access TX on network layer Write to character device Timer setup, etc. KVM: x86/mmu: Page fault and MMIO cleanups This is a combination of prep work for TDX and SNP, and a clean up of the page fault path to (hopefully) make it easier to follow the rules for private qemu-kvm中的MMIO 我们知道X86体系结构上对设备进行访问可以通过PIO方式和MMIO (Memory Mapped I/O)两种方式进行，那么QEMU-KVM具体是如何实现设备MMIO访问的呢？ KVM如何标记EPT是MMIO类型 ? hardware_setup时候虚拟机如果开启了ept支持就调用ept_set_mmio_spte_mask初始化 shadow_mmio_mask， 设置EPT页表项最低3bit为：110b就会触 ARM_SMCCC_KVM_FUNC_MMIO_GUARD ¶ Request that a given memory region is handled as MMIO by the hypervisor, allowing accesses to this region to be emulated by the KVM host. You initialize these with memory_region_init_io (), passing it a The goal is to give a QEMU/KVM VM direct access to a physical memory-mapped SD Host Controller through VFIO on an ARM embedded SoC, in that case, a Zynq UltraScale+ MPSoC (ZCU104). like IOMMUFD [1] or KVM. MMIO Exit（MMIO 退出）的本质 (1) 什么是 MMIO Exit？ 定义：当虚拟机尝试访问一个 MMIO 区域 （设备寄存器映射的内存地址）时，CPU 触发 VM Exit，将控制权交还给虚拟机监控器（VMM，如 文章阐述了相关API的使用，如`memory_region_add_coalescing`和`memory_region_clear_coalescing`等，并讲解了如何通过KVM注册和注 MMIO地址引起的EPT退出MMIO地址引起的EPT退出MMIO是通过设置spte的保留位来标志的。虚拟机内部第一次访问MMIO的gpa时，发生了EPT_VIOLATION然 I'm trying to build a minimal kvm based hypervisor and I want to track reads and writes in the hosts userspace. com MMIO，通过内存读写制定操作IO，这种则比较常见，例如pci设备的bar，或者其他系统寄存器，例如local apic的基址0xFEE00000； PIO的处理相对直接，直接handle_io ()入口；而MMIO的处理过程则 本文基于以下软硬件假定： 架构：AARCH64 内核版本：5. As we know the QEMU doesn’t commit the MMIO memory region, so pfn is ‘KVM_PFN_NOSLOT’ and then mark the spte with ‘shadow_mmio_mask’. __direct_map will be called to Make sure you understand what file descriptor to use and when, we use the KVM fd when calling KVM_CREATE_VM, but when interacting with the vm such as calling 总结 MMIO是通过设置spte的保留位来标志的． 虚拟机内部第一次访问MMIO的gpa时，发生了EPT_VIOLATION然后check gpa发现对应的pfn不存在（QEMU没有注册），那么认为这是 4. h) is responsible for presenting a standard x86 mmu to the guest, while translating guest physical Hacky Integration (Red Hat Virt Team, Peter Xu) QEMU Instantiate 1 virtio MMIO bus Bypass MSI region in virtio-iommu device Guest Kernel Pass device mmio window via boot param (no FW Linux Kernel: Re: [PATCH 14/14] KVM: x86: Add helpers to prepare kvm_run for userspace MMIO exit Paolo Bonzini – KVM Forum 2013 I/O thread QEMU architecture (now) select() nsec Timers Event loop BH cpu_exec (KVM) cpu_exec (KVM) fd Timers AioContext GMainLoop Migration VNC SPICE mmio. The adding of dma_buf_get_pfn_unlocked() in this. [ch] and paging_tmpl. Linux Kernel: [PATCH 04/14] KVM: x86: Use local MMIO fragment variable to clean up emulator_read_write () Add a sanity check to ensure KVM doesn't use an on-stack variable when handling an MMIO request for an SEV-ES guest. Availability of these By leveraging CVE-2021-3929 and CVE-2021-3947, we trigger scatter-gather DMA operations to MMIO regions, and the first MMIO write is to the malloc primitive in the HDA device, allocating three chunks For PIO, we can set the VMCS to intercept the specified port. h>#include <trace/events/kvm. Since your patch is better, I'll push that one instead as soon as I get confirmation. h " Include dependency graph for mmio. Explains KVM and QEMU architecture: Intel VT-x/AMD-V hardware extensions, the KVM kernel module API, QEMU device emulation, VM exit handling, virtio paravirtual I/O, and live migration. The host platform is a ZynqMP SoC. 6 MMIO机制 虚拟设备MMIO实现原理 MMIO的机制简单介绍如下：QEMU申明一段内存作为MMIO内存，SeaBIOS会分配好所有设备MMIO对应的基址，当Guest第一次访问MMIO的地址时候，会发 4. KVM architecture QEMU code generally runs under global mutex Guest execution vmexit handling (PIO/MMIO dispatch) vcpu thread Guest execution vmexit handling (PIO/MMIO dispatch) vcpu works Guest DMA Proxy Device Memory-mapped I/O (MMIO) directly accesses device directly injected into guest using interrupt virtualization features enforced by host IOMMU device resides on an 对于设备的MMIO空间访问,则可以通过建立EPT页表将设备的MMIO物理内存映射到虚拟的MMIO地址空间,让虚拟机能够直接通过MMIO访问PCI设备的bar空间,提高IO性能. When the guest later access this MMIO 本文分析了Linux内存管理中的MMIO技术，解释了MMIO与PIO的区别及其在虚拟化环境中的应用。通过具体示例，阐述了MMIO的内存布局、PCI地 The memory model provides support for tracking RAM changes by the guest setting up coalesced memory for kvm setting up ioeventfd regions for kvm Memory is modelled as an acyclic graph of As we know the QEMU doesn’t commit the MMIO memory region, so pfn is ‘KVM_PFN_NOSLOT’ and then mark the spte with ‘shadow_mmio_mask’. The proposed Linux ioregionfd interface reduces context switches and overhead by enabling direct, file descriptor–based dispatch of MMIO operations, bypassing the traditional need to exit to I'm trying to build a minimal kvm based hypervisor and I want to track reads and writes in the hosts userspace.
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