lwn.git/Documentation/virtual, branch docs-5.2a

Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm

2019-03-15T22:00:28+00:00

Pull KVM updates from Paolo Bonzini: "ARM: - some cleanups - direct physical timer assignment - cache sanitization for 32-bit guests s390: - interrupt cleanup - introduction of the Guest Information Block - preparation for processor subfunctions in cpu models PPC: - bug fixes and improvements, especially related to machine checks and protection keys x86: - many, many cleanups, including removing a bunch of MMU code for unnecessary optimizations - AVIC fixes Generic: - memcg accounting" * tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (147 commits) kvm: vmx: fix formatting of a comment KVM: doc: Document the life cycle of a VM and its resources MAINTAINERS: Add KVM selftests to existing KVM entry Revert "KVM/MMU: Flush tlb directly in the kvm_zap_gfn_range()" KVM: PPC: Book3S: Add count cache flush parameters to kvmppc_get_cpu_char() KVM: PPC: Fix compilation when KVM is not enabled KVM: Minor cleanups for kvm_main.c KVM: s390: add debug logging for cpu model subfunctions KVM: s390: implement subfunction processor calls arm64: KVM: Fix architecturally invalid reset value for FPEXC32_EL2 KVM: arm/arm64: Remove unused timer variable KVM: PPC: Book3S: Improve KVM reference counting KVM: PPC: Book3S HV: Fix build failure without IOMMU support Revert "KVM: Eliminate extra function calls in kvm_get_dirty_log_protect()" x86: kvmguest: use TSC clocksource if invariant TSC is exposed KVM: Never start grow vCPU halt_poll_ns from value below halt_poll_ns_grow_start KVM: Expose the initial start value in grow_halt_poll_ns() as a module parameter KVM: grow_halt_poll_ns() should never shrink vCPU halt_poll_ns KVM: x86/mmu: Consolidate kvm_mmu_zap_all() and kvm_mmu_zap_mmio_sptes() KVM: x86/mmu: WARN if zapping a MMIO spte results in zapping children ...

KVM: doc: Document the life cycle of a VM and its resources

2019-03-15T18:24:33+00:00

The series to add memcg accounting to KVM allocations[1] states: There are many KVM kernel memory allocations which are tied to the life of the VM process and should be charged to the VM process's cgroup. While it is correct to account KVM kernel allocations to the cgroup of the process that created the VM, it's technically incorrect to state that the KVM kernel memory allocations are tied to the life of the VM process. This is because the VM itself, i.e. struct kvm, is not tied to the life of the process which created it, rather it is tied to the life of its associated file descriptor. In other words, kvm_destroy_vm() is not invoked until fput() decrements its associated file's refcount to zero. A simple example is to fork() in Qemu and have the child sleep indefinitely; kvm_destroy_vm() isn't called until Qemu closes its file descriptor *and* the rogue child is killed. The allocations are guaranteed to be *accounted* to the process which created the VM, but only because KVM's per-{VM,vCPU} ioctls reject the ioctl() with -EIO if kvm->mm != current->mm. I.e. the child can keep the VM "alive" but can't do anything useful with its reference. Note that because 'struct kvm' also holds a reference to the mm_struct of its owner, the above behavior also applies to userspace allocations. Given that mucking with a VM's file descriptor can lead to subtle and undesirable behavior, e.g. memcg charges persisting after a VM is shut down, explicitly document a VM's lifecycle and its impact on the VM's resources. Alternatively, KVM could aggressively free resources when the creating process exits, e.g. via mmu_notifier->release(). However, mmu_notifier isn't guaranteed to be available, and freeing resources when the creator exits is likely to be error prone and fragile as KVM would need to ensure that it only freed resources that are truly out of reach. In practice, the existing behavior shouldn't be problematic as a properly configured system will prevent a child process from being moved out of the appropriate cgroup hierarchy, i.e. prevent hiding the process from the OOM killer, and will prevent an unprivileged user from being able to to hold a reference to struct kvm via another method, e.g. debugfs. [1]https://patchwork.kernel.org/patch/10806707/ Signed-off-by: Sean Christopherson Signed-off-by: Paolo Bonzini

virtio-ccw: diag 500 may return a negative cookie

2019-03-06T16:19:33+00:00

If something goes wrong in the kvm io bus handling, the virtio-ccw diagnose may return a negative error value in the cookie gpr. Document this. Reviewed-by: Halil Pasic Signed-off-by: Cornelia Huck Signed-off-by: Michael S. Tsirkin

KVM: Expose the initial start value in grow_halt_poll_ns() as a module parameter

2019-02-20T21:48:50+00:00

The hard-coded value 10000 in grow_halt_poll_ns() stands for the initial start value when raising up vcpu->halt_poll_ns. It actually sets the first timeout to the first polling session. This value has significant effect on how tolerant we are to outliers. On the standard case, higher value is better - we will spend more time in the polling busyloop, handle events/interrupts faster and result in better performance. But on outliers it puts us in a busy loop that does nothing. Even if the shrink factor is zero, we will still waste time on the first iteration. The optimal value changes between different workloads. It depends on outliers rate and polling sessions length. As this value has significant effect on the dynamic halt-polling algorithm, it should be configurable and exposed. Reviewed-by: Boris Ostrovsky Reviewed-by: Liran Alon Signed-off-by: Nir Weiner Signed-off-by: Paolo Bonzini

Revert "KVM: MMU: document fast invalidate all pages"

2019-02-20T21:48:39+00:00

Remove x86 KVM's fast invalidate mechanism, i.e. revert all patches from the original series[1]. Though not explicitly stated, for all intents and purposes the fast invalidate mechanism was added to speed up the scenario where removing a memslot, e.g. as part of accessing reading PCI ROM, caused KVM to flush all shadow entries[1]. Now that the memslot case flushes only shadow entries belonging to the memslot, i.e. doesn't use the fast invalidate mechanism, the only remaining usage of the mechanism are when the VM is being destroyed and when the MMIO generation rolls over. When a VM is being destroyed, either there are no active vcpus, i.e. there's no lock contention, or the VM has ungracefully terminated, in which case we want to reclaim its pages as quickly as possible, i.e. not release the MMU lock if there are still CPUs executing in the VM. The MMIO generation scenario is almost literally a one-in-a-million occurrence, i.e. is not a performance sensitive scenario. Given that lock-breaking is not desirable (VM teardown) or irrelevant (MMIO generation overflow), remove the fast invalidate mechanism to simplify the code (a small amount) and to discourage future code from zapping all pages as using such a big hammer should be a last restort. This reverts commit f6f8adeef542a18b1cb26a0b772c9781a10bb477. [1] https://lkml.kernel.org/r/1369960590-14138-1-git-send-email-xiaoguangrong@linux.vnet.ibm.com Cc: Xiao Guangrong Signed-off-by: Sean Christopherson Signed-off-by: Paolo Bonzini

KVM: Move the memslot update in-progress flag to bit 63

2019-02-20T21:48:37+00:00

...now that KVM won't explode by moving it out of bit 0. Using bit 63 eliminates the need to jump over bit 0, e.g. when calculating a new memslots generation or when propagating the memslots generation to an MMIO spte. Signed-off-by: Sean Christopherson Signed-off-by: Paolo Bonzini

Documentation/virtual/kvm: Update URL for AMD SEV API specification

2019-01-11T17:38:07+00:00

The URL of [api-spec] in Documentation/virtual/kvm/amd-memory-encryption.rst is no longer valid, replaced space with underscore. Signed-off-by: Christophe de Dinechin Reviewed-by: Brijesh Singh Signed-off-by: Radim Krčmář

x86/kvm/hyper-v: Introduce KVM_GET_SUPPORTED_HV_CPUID

2018-12-14T16:59:54+00:00

With every new Hyper-V Enlightenment we implement we're forced to add a KVM_CAP_HYPERV_* capability. While this approach works it is fairly inconvenient: the majority of the enlightenments we do have corresponding CPUID feature bit(s) and userspace has to know this anyways to be able to expose the feature to the guest. Add KVM_GET_SUPPORTED_HV_CPUID ioctl (backed by KVM_CAP_HYPERV_CPUID, "one cap to rule them all!") returning all Hyper-V CPUID feature leaves. Using the existing KVM_GET_SUPPORTED_CPUID doesn't seem to be possible: Hyper-V CPUID feature leaves intersect with KVM's (e.g. 0x40000000, 0x40000001) and we would probably confuse userspace in case we decide to return these twice. KVM_CAP_HYPERV_CPUID's number is interim: we're intended to drop KVM_CAP_HYPERV_STIMER_DIRECT and use its number instead. Suggested-by: Paolo Bonzini Signed-off-by: Vitaly Kuznetsov Signed-off-by: Paolo Bonzini

kvm: introduce manual dirty log reprotect

2018-12-14T11:34:19+00:00

There are two problems with KVM_GET_DIRTY_LOG. First, and less important, it can take kvm->mmu_lock for an extended period of time. Second, its user can actually see many false positives in some cases. The latter is due to a benign race like this: 1. KVM_GET_DIRTY_LOG returns a set of dirty pages and write protects them. 2. The guest modifies the pages, causing them to be marked ditry. 3. Userspace actually copies the pages. 4. KVM_GET_DIRTY_LOG returns those pages as dirty again, even though they were not written to since (3). This is especially a problem for large guests, where the time between (1) and (3) can be substantial. This patch introduces a new capability which, when enabled, makes KVM_GET_DIRTY_LOG not write-protect the pages it returns. Instead, userspace has to explicitly clear the dirty log bits just before using the content of the page. The new KVM_CLEAR_DIRTY_LOG ioctl can also operate on a 64-page granularity rather than requiring to sync a full memslot; this way, the mmu_lock is taken for small amounts of time, and only a small amount of time will pass between write protection of pages and the sending of their content. Signed-off-by: Paolo Bonzini

kvm: make KVM_CAP_ENABLE_CAP_VM architecture agnostic

2018-12-14T11:34:18+00:00

The first such capability to be handled in virt/kvm/ will be manual dirty page reprotection. Signed-off-by: Paolo Bonzini