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Commit92b5265d38("KVM: Depend on HIGH_RES_TIMERS") added a dependency to high resolution timers with the comment: KVM lapic timer and tsc deadline timer based on hrtimer, setting a leftmost node to rb tree and then do hrtimer reprogram. If hrtimer not configured as high resolution, hrtimer_enqueue_reprogram do nothing and then make kvm lapic timer and tsc deadline timer fail. That was back in 2012, where hrtimer_start_range_ns() would do the reprogramming with hrtimer_enqueue_reprogram(). But as that was a nop with high resolution timers disabled, this did not work. But a lot has changed in the last 12 years. For example, commit49a2a07514("hrtimer: Kick lowres dynticks targets on timer enqueue") modifies __hrtimer_start_range_ns() to work with low res timers. There's been lots of other changes that make low res work. ChromeOS has tested this before as well, and it hasn't seen any issues with running KVM with high res timers disabled. There could be problems, especially at low HZ, for guests that do not support kvmclock and rely on precise delivery of periodic timers to keep their clock running. This can be the APIC timer (provided by the kernel), the RTC (provided by userspace), or the i8254 (choice of kernel/userspace). These guests are few and far between these days, and in the case of the APIC timer + Intel hosts we can use the preemption timer (which is TSC-based and has better latency _and_ accuracy). In KVM, only x86 is requiring CONFIG_HIGH_RES_TIMERS; perhaps a "depends on HIGH_RES_TIMERS || EXPERT" could be added to virt/kvm, or a pr_warn could be added to kvm_init if HIGH_RES_TIMERS are not enabled. But in general, it seems that there must be other code in the kernel (maybe sound/?) that is relying on having high-enough HZ or hrtimers but that's not documented anywhere. Whenever you disable it you probably need to know what you're doing and what your workload is; so the dependency is not particularly interesting, and we can just remove it. Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> Message-ID: <20240821095127.45d17b19@gandalf.local.home> [Added the last two paragraphs to the commit message. - Paolo] Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
213 lines
6.5 KiB
Plaintext
213 lines
6.5 KiB
Plaintext
# SPDX-License-Identifier: GPL-2.0
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#
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# KVM configuration
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#
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source "virt/kvm/Kconfig"
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menuconfig VIRTUALIZATION
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bool "Virtualization"
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default y
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help
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Say Y here to get to see options for using your Linux host to run other
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operating systems inside virtual machines (guests).
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This option alone does not add any kernel code.
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If you say N, all options in this submenu will be skipped and disabled.
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if VIRTUALIZATION
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config KVM
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tristate "Kernel-based Virtual Machine (KVM) support"
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depends on X86_LOCAL_APIC
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select KVM_COMMON
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select KVM_GENERIC_MMU_NOTIFIER
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select HAVE_KVM_IRQCHIP
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select HAVE_KVM_PFNCACHE
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select HAVE_KVM_DIRTY_RING_TSO
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select HAVE_KVM_DIRTY_RING_ACQ_REL
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select HAVE_KVM_IRQ_BYPASS
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select HAVE_KVM_IRQ_ROUTING
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select HAVE_KVM_READONLY_MEM
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select KVM_ASYNC_PF
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select USER_RETURN_NOTIFIER
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select KVM_MMIO
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select SCHED_INFO
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select PERF_EVENTS
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select GUEST_PERF_EVENTS
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select HAVE_KVM_MSI
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select HAVE_KVM_CPU_RELAX_INTERCEPT
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select HAVE_KVM_NO_POLL
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select KVM_XFER_TO_GUEST_WORK
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select KVM_GENERIC_DIRTYLOG_READ_PROTECT
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select KVM_VFIO
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select HAVE_KVM_PM_NOTIFIER if PM
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select KVM_GENERIC_HARDWARE_ENABLING
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select KVM_GENERIC_PRE_FAULT_MEMORY
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select KVM_WERROR if WERROR
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help
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Support hosting fully virtualized guest machines using hardware
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virtualization extensions. You will need a fairly recent
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processor equipped with virtualization extensions. You will also
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need to select one or more of the processor modules below.
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This module provides access to the hardware capabilities through
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a character device node named /dev/kvm.
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To compile this as a module, choose M here: the module
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will be called kvm.
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If unsure, say N.
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config KVM_WERROR
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bool "Compile KVM with -Werror"
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# Disallow KVM's -Werror if KASAN is enabled, e.g. to guard against
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# randomized configs from selecting KVM_WERROR=y, which doesn't play
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# nice with KASAN. KASAN builds generates warnings for the default
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# FRAME_WARN, i.e. KVM_WERROR=y with KASAN=y requires special tuning.
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# Building KVM with -Werror and KASAN is still doable via enabling
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# the kernel-wide WERROR=y.
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depends on KVM && ((EXPERT && !KASAN) || WERROR)
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help
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Add -Werror to the build flags for KVM.
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If in doubt, say "N".
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config KVM_SW_PROTECTED_VM
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bool "Enable support for KVM software-protected VMs"
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depends on EXPERT
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depends on KVM && X86_64
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select KVM_GENERIC_PRIVATE_MEM
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help
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Enable support for KVM software-protected VMs. Currently, software-
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protected VMs are purely a development and testing vehicle for
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KVM_CREATE_GUEST_MEMFD. Attempting to run a "real" VM workload as a
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software-protected VM will fail miserably.
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If unsure, say "N".
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config KVM_INTEL
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tristate "KVM for Intel (and compatible) processors support"
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depends on KVM && IA32_FEAT_CTL
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help
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Provides support for KVM on processors equipped with Intel's VT
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extensions, a.k.a. Virtual Machine Extensions (VMX).
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To compile this as a module, choose M here: the module
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will be called kvm-intel.
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config KVM_INTEL_PROVE_VE
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bool "Check that guests do not receive #VE exceptions"
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depends on KVM_INTEL && EXPERT
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help
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Checks that KVM's page table management code will not incorrectly
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let guests receive a virtualization exception. Virtualization
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exceptions will be trapped by the hypervisor rather than injected
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in the guest.
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Note: some CPUs appear to generate spurious EPT Violations #VEs
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that trigger KVM's WARN, in particular with eptad=0 and/or nested
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virtualization.
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If unsure, say N.
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config X86_SGX_KVM
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bool "Software Guard eXtensions (SGX) Virtualization"
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depends on X86_SGX && KVM_INTEL
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help
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Enables KVM guests to create SGX enclaves.
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This includes support to expose "raw" unreclaimable enclave memory to
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guests via a device node, e.g. /dev/sgx_vepc.
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If unsure, say N.
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config KVM_AMD
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tristate "KVM for AMD processors support"
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depends on KVM && (CPU_SUP_AMD || CPU_SUP_HYGON)
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help
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Provides support for KVM on AMD processors equipped with the AMD-V
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(SVM) extensions.
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To compile this as a module, choose M here: the module
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will be called kvm-amd.
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config KVM_AMD_SEV
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bool "AMD Secure Encrypted Virtualization (SEV) support"
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default y
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depends on KVM_AMD && X86_64
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depends on CRYPTO_DEV_SP_PSP && !(KVM_AMD=y && CRYPTO_DEV_CCP_DD=m)
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select ARCH_HAS_CC_PLATFORM
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select KVM_GENERIC_PRIVATE_MEM
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select HAVE_KVM_ARCH_GMEM_PREPARE
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select HAVE_KVM_ARCH_GMEM_INVALIDATE
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help
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Provides support for launching encrypted VMs which use Secure
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Encrypted Virtualization (SEV), Secure Encrypted Virtualization with
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Encrypted State (SEV-ES), and Secure Encrypted Virtualization with
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Secure Nested Paging (SEV-SNP) technologies on AMD processors.
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config KVM_SMM
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bool "System Management Mode emulation"
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default y
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depends on KVM
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help
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Provides support for KVM to emulate System Management Mode (SMM)
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in virtual machines. This can be used by the virtual machine
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firmware to implement UEFI secure boot.
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If unsure, say Y.
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config KVM_HYPERV
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bool "Support for Microsoft Hyper-V emulation"
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depends on KVM
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default y
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help
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Provides KVM support for emulating Microsoft Hyper-V. This allows KVM
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to expose a subset of the paravirtualized interfaces defined in the
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Hyper-V Hypervisor Top-Level Functional Specification (TLFS):
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https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/reference/tlfs
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These interfaces are required for the correct and performant functioning
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of Windows and Hyper-V guests on KVM.
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If unsure, say "Y".
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config KVM_XEN
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bool "Support for Xen hypercall interface"
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depends on KVM
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help
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Provides KVM support for the hosting Xen HVM guests and
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passing Xen hypercalls to userspace.
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If in doubt, say "N".
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config KVM_PROVE_MMU
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bool "Prove KVM MMU correctness"
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depends on DEBUG_KERNEL
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depends on KVM
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depends on EXPERT
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help
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Enables runtime assertions in KVM's MMU that are too costly to enable
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in anything remotely resembling a production environment, e.g. this
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gates code that verifies a to-be-freed page table doesn't have any
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present SPTEs.
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If in doubt, say "N".
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config KVM_EXTERNAL_WRITE_TRACKING
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bool
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config KVM_MAX_NR_VCPUS
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int "Maximum number of vCPUs per KVM guest"
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depends on KVM
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range 1024 4096
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default 4096 if MAXSMP
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default 1024
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help
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Set the maximum number of vCPUs per KVM guest. Larger values will increase
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the memory footprint of each KVM guest, regardless of how many vCPUs are
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created for a given VM.
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endif # VIRTUALIZATION
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