diff options
Diffstat (limited to 'Documentation/virt/kvm/api.rst')
| -rw-r--r-- | Documentation/virt/kvm/api.rst | 146 |
1 files changed, 129 insertions, 17 deletions
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index e00a66d72372..99ceb978c8b0 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -262,6 +262,18 @@ The KVM_RUN ioctl (cf.) communicates with userspace via a shared memory region. This ioctl returns the size of that region. See the KVM_RUN documentation for details. +Besides the size of the KVM_RUN communication region, other areas of +the VCPU file descriptor can be mmap-ed, including: + +- 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_GET_VCPU_MMAP_SIZE. + KVM_CAP_COALESCED_MMIO is not documented yet. + +- if KVM_CAP_DIRTY_LOG_RING is available, a number of pages at + KVM_DIRTY_LOG_PAGE_OFFSET * PAGE_SIZE. For more information on + KVM_CAP_DIRTY_LOG_RING, see section 8.3. + 4.6 KVM_SET_MEMORY_REGION ------------------------- @@ -348,10 +360,9 @@ since the last call to this ioctl. Bit 0 is the first page in the memory slot. Ensure the entire structure is cleared to avoid padding issues. -If KVM_CAP_MULTI_ADDRESS_SPACE is available, bits 16-31 specifies -the address space for which you want to return the dirty bitmap. -They must be less than the value that KVM_CHECK_EXTENSION returns for -the KVM_CAP_MULTI_ADDRESS_SPACE capability. +If KVM_CAP_MULTI_ADDRESS_SPACE is available, bits 16-31 of slot field specifies +the address space for which you want to return the dirty bitmap. See +KVM_SET_USER_MEMORY_REGION for details on the usage of slot field. The bits in the dirty bitmap are cleared before the ioctl returns, unless KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 is enabled. For more information, @@ -380,9 +391,14 @@ This ioctl is obsolete and has been removed. Errors: - ===== ============================= + ======= ============================================================== EINTR an unmasked signal is pending - ===== ============================= + ENOEXEC the vcpu hasn't been initialized or the guest tried to execute + instructions from device memory (arm64) + ENOSYS data abort outside memslots with no syndrome info and + KVM_CAP_ARM_NISV_TO_USER not enabled (arm64) + EPERM SVE feature set but not finalized (arm64) + ======= ============================================================== This ioctl is used to run a guest virtual cpu. While there are no explicit parameters, there is an implicit parameter block that can be @@ -1264,6 +1280,9 @@ field userspace_addr, which must point at user addressable memory for the entire memory slot size. Any object may back this memory, including anonymous memory, ordinary files, and hugetlbfs. +On architectures that support a form of address tagging, userspace_addr must +be an untagged address. + It is recommended that the lower 21 bits of guest_phys_addr and userspace_addr be identical. This allows large pages in the guest to be backed by large pages in the host. @@ -1316,7 +1335,7 @@ documentation when it pops into existence). :Capability: KVM_CAP_ENABLE_CAP_VM :Architectures: all -:Type: vcpu ioctl +:Type: vm ioctl :Parameters: struct kvm_enable_cap (in) :Returns: 0 on success; -1 on error @@ -4415,7 +4434,7 @@ to I/O ports. :Capability: KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 :Architectures: x86, arm, arm64, mips :Type: vm ioctl -:Parameters: struct kvm_dirty_log (in) +:Parameters: struct kvm_clear_dirty_log (in) :Returns: 0 on success, -1 on error :: @@ -4442,10 +4461,9 @@ in KVM's dirty bitmap, and dirty tracking is re-enabled for that page (for example via write-protection, or by clearing the dirty bit in a page table entry). -If KVM_CAP_MULTI_ADDRESS_SPACE is available, bits 16-31 specifies -the address space for which you want to return the dirty bitmap. -They must be less than the value that KVM_CHECK_EXTENSION returns for -the KVM_CAP_MULTI_ADDRESS_SPACE capability. +If KVM_CAP_MULTI_ADDRESS_SPACE is available, bits 16-31 of slot field specifies +the address space for which you want to clear the dirty status. See +KVM_SET_USER_MEMORY_REGION for details on the usage of slot field. This ioctl is mostly useful when KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 is enabled; for more information, see the description of the capability. @@ -4455,9 +4473,9 @@ that KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 is present. 4.118 KVM_GET_SUPPORTED_HV_CPUID -------------------------------- -:Capability: KVM_CAP_HYPERV_CPUID +:Capability: KVM_CAP_HYPERV_CPUID (vcpu), KVM_CAP_SYS_HYPERV_CPUID (system) :Architectures: x86 -:Type: vcpu ioctl +:Type: system ioctl, vcpu ioctl :Parameters: struct kvm_cpuid2 (in/out) :Returns: 0 on success, -1 on error @@ -4502,9 +4520,6 @@ Currently, the following list of CPUID leaves are returned: - HYPERV_CPUID_SYNDBG_INTERFACE - HYPERV_CPUID_SYNDBG_PLATFORM_CAPABILITIES -HYPERV_CPUID_NESTED_FEATURES leaf is only exposed when Enlightened VMCS was -enabled on the corresponding vCPU (KVM_CAP_HYPERV_ENLIGHTENED_VMCS). - Userspace invokes KVM_GET_SUPPORTED_HV_CPUID by passing a kvm_cpuid2 structure with the 'nent' field indicating the number of entries in the variable-size array 'entries'. If the number of entries is too low to describe all Hyper-V @@ -4515,6 +4530,15 @@ number of valid entries in the 'entries' array, which is then filled. 'index' and 'flags' fields in 'struct kvm_cpuid_entry2' are currently reserved, userspace should not expect to get any particular value there. +Note, vcpu version of KVM_GET_SUPPORTED_HV_CPUID is currently deprecated. Unlike +system ioctl which exposes all supported feature bits unconditionally, vcpu +version has the following quirks: +- HYPERV_CPUID_NESTED_FEATURES leaf and HV_X64_ENLIGHTENED_VMCS_RECOMMENDED + feature bit are only exposed when Enlightened VMCS was previously enabled + on the corresponding vCPU (KVM_CAP_HYPERV_ENLIGHTENED_VMCS). +- HV_STIMER_DIRECT_MODE_AVAILABLE bit is only exposed with in-kernel LAPIC. + (presumes KVM_CREATE_IRQCHIP has already been called). + 4.119 KVM_ARM_VCPU_FINALIZE --------------------------- @@ -6390,3 +6414,91 @@ When enabled, KVM will disable paravirtual features provided to the guest according to the bits in the KVM_CPUID_FEATURES CPUID leaf (0x40000001). Otherwise, a guest may use the paravirtual features regardless of what has actually been exposed through the CPUID leaf. + + +8.29 KVM_CAP_DIRTY_LOG_RING +--------------------------- + +:Architectures: x86 +:Parameters: args[0] - size of the dirty log ring + +KVM is capable of tracking dirty memory using ring buffers that are +mmaped into userspace; there is one dirty ring per vcpu. + +The dirty ring is available to userspace as an array of +``struct kvm_dirty_gfn``. Each dirty entry it's defined as:: + + struct kvm_dirty_gfn { + __u32 flags; + __u32 slot; /* as_id | slot_id */ + __u64 offset; + }; + +The following values are defined for the flags field to define the +current state of the entry:: + + #define KVM_DIRTY_GFN_F_DIRTY BIT(0) + #define KVM_DIRTY_GFN_F_RESET BIT(1) + #define KVM_DIRTY_GFN_F_MASK 0x3 + +Userspace should call KVM_ENABLE_CAP ioctl right after KVM_CREATE_VM +ioctl to enable this capability for the new guest and set the size of +the rings. Enabling the capability is only allowed before creating any +vCPU, and the size of the ring must be a power of two. The larger the +ring buffer, the less likely the ring is full and the VM is forced to +exit to userspace. The optimal size depends on the workload, but it is +recommended that it be at least 64 KiB (4096 entries). + +Just like for dirty page bitmaps, the buffer tracks writes to +all user memory regions for which the KVM_MEM_LOG_DIRTY_PAGES flag was +set in KVM_SET_USER_MEMORY_REGION. Once a memory region is registered +with the flag set, userspace can start harvesting dirty pages from the +ring buffer. + +An entry in the ring buffer can be unused (flag bits ``00``), +dirty (flag bits ``01``) or harvested (flag bits ``1X``). The +state machine for the entry is as follows:: + + dirtied harvested reset + 00 -----------> 01 -------------> 1X -------+ + ^ | + | | + +------------------------------------------+ + +To harvest the dirty pages, userspace accesses the mmaped ring buffer +to read the dirty GFNs. If the flags has the DIRTY bit set (at this stage +the RESET bit must be cleared), then it means this GFN is a dirty GFN. +The userspace should harvest this GFN and mark the flags from state +``01b`` to ``1Xb`` (bit 0 will be ignored by KVM, but bit 1 must be set +to show that this GFN is harvested and waiting for a reset), and move +on to the next GFN. The userspace should continue to do this until the +flags of a GFN have the DIRTY bit cleared, meaning that it has harvested +all the dirty GFNs that were available. + +It's not necessary for userspace to harvest the all dirty GFNs at once. +However it must collect the dirty GFNs in sequence, i.e., the userspace +program cannot skip one dirty GFN to collect the one next to it. + +After processing one or more entries in the ring buffer, userspace +calls the VM ioctl KVM_RESET_DIRTY_RINGS to notify the kernel about +it, so that the kernel will reprotect those collected GFNs. +Therefore, the ioctl must be called *before* reading the content of +the dirty pages. + +The dirty ring can get full. When it happens, the KVM_RUN of the +vcpu will return with exit reason KVM_EXIT_DIRTY_LOG_FULL. + +The dirty ring interface has a major difference comparing to the +KVM_GET_DIRTY_LOG interface in that, when reading the dirty ring from +userspace, it's still possible that the kernel has not yet flushed the +processor's dirty page buffers into the kernel buffer (with dirty bitmaps, the +flushing is done by the KVM_GET_DIRTY_LOG ioctl). To achieve that, one +needs to kick the vcpu out of KVM_RUN using a signal. The resulting +vmexit ensures that all dirty GFNs are flushed to the dirty rings. + +NOTE: the capability KVM_CAP_DIRTY_LOG_RING and the corresponding +ioctl KVM_RESET_DIRTY_RINGS are mutual exclusive to the existing ioctls +KVM_GET_DIRTY_LOG and KVM_CLEAR_DIRTY_LOG. After enabling +KVM_CAP_DIRTY_LOG_RING with an acceptable dirty ring size, the virtual +machine will switch to ring-buffer dirty page tracking and further +KVM_GET_DIRTY_LOG or KVM_CLEAR_DIRTY_LOG ioctls will fail. |