diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/kvm/api.txt | 208 | ||||
| -rw-r--r-- | Documentation/kvm/cpuid.txt | 42 | ||||
| -rw-r--r-- | Documentation/kvm/mmu.txt | 304 |
3 files changed, 552 insertions, 2 deletions
diff --git a/Documentation/kvm/api.txt b/Documentation/kvm/api.txt index c6416a398163..a237518e51b9 100644 --- a/Documentation/kvm/api.txt +++ b/Documentation/kvm/api.txt @@ -656,6 +656,7 @@ struct kvm_clock_data { 4.29 KVM_GET_VCPU_EVENTS Capability: KVM_CAP_VCPU_EVENTS +Extended by: KVM_CAP_INTR_SHADOW Architectures: x86 Type: vm ioctl Parameters: struct kvm_vcpu_event (out) @@ -676,7 +677,7 @@ struct kvm_vcpu_events { __u8 injected; __u8 nr; __u8 soft; - __u8 pad; + __u8 shadow; } interrupt; struct { __u8 injected; @@ -688,9 +689,13 @@ struct kvm_vcpu_events { __u32 flags; }; +KVM_VCPUEVENT_VALID_SHADOW may be set in the flags field to signal that +interrupt.shadow contains a valid state. Otherwise, this field is undefined. + 4.30 KVM_SET_VCPU_EVENTS Capability: KVM_CAP_VCPU_EVENTS +Extended by: KVM_CAP_INTR_SHADOW Architectures: x86 Type: vm ioctl Parameters: struct kvm_vcpu_event (in) @@ -709,6 +714,183 @@ current in-kernel state. The bits are: KVM_VCPUEVENT_VALID_NMI_PENDING - transfer nmi.pending to the kernel KVM_VCPUEVENT_VALID_SIPI_VECTOR - transfer sipi_vector +If KVM_CAP_INTR_SHADOW is available, KVM_VCPUEVENT_VALID_SHADOW can be set in +the flags field to signal that interrupt.shadow contains a valid state and +shall be written into the VCPU. + +4.32 KVM_GET_DEBUGREGS + +Capability: KVM_CAP_DEBUGREGS +Architectures: x86 +Type: vm ioctl +Parameters: struct kvm_debugregs (out) +Returns: 0 on success, -1 on error + +Reads debug registers from the vcpu. + +struct kvm_debugregs { + __u64 db[4]; + __u64 dr6; + __u64 dr7; + __u64 flags; + __u64 reserved[9]; +}; + +4.33 KVM_SET_DEBUGREGS + +Capability: KVM_CAP_DEBUGREGS +Architectures: x86 +Type: vm ioctl +Parameters: struct kvm_debugregs (in) +Returns: 0 on success, -1 on error + +Writes debug registers into the vcpu. + +See KVM_GET_DEBUGREGS for the data structure. The flags field is unused +yet and must be cleared on entry. + +4.34 KVM_SET_USER_MEMORY_REGION + +Capability: KVM_CAP_USER_MEM +Architectures: all +Type: vm ioctl +Parameters: struct kvm_userspace_memory_region (in) +Returns: 0 on success, -1 on error + +struct kvm_userspace_memory_region { + __u32 slot; + __u32 flags; + __u64 guest_phys_addr; + __u64 memory_size; /* bytes */ + __u64 userspace_addr; /* start of the userspace allocated memory */ +}; + +/* for kvm_memory_region::flags */ +#define KVM_MEM_LOG_DIRTY_PAGES 1UL + +This ioctl allows the user to create or modify a guest physical memory +slot. When changing an existing slot, it may be moved in the guest +physical memory space, or its flags may be modified. It may not be +resized. Slots may not overlap in guest physical address space. + +Memory for the region is taken starting at the address denoted by the +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. + +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. + +The flags field supports just one flag, KVM_MEM_LOG_DIRTY_PAGES, which +instructs kvm to keep track of writes to memory within the slot. See +the KVM_GET_DIRTY_LOG ioctl. + +When the KVM_CAP_SYNC_MMU capability, changes in the backing of the memory +region are automatically reflected into the guest. For example, an mmap() +that affects the region will be made visible immediately. Another example +is madvise(MADV_DROP). + +It is recommended to use this API instead of the KVM_SET_MEMORY_REGION ioctl. +The KVM_SET_MEMORY_REGION does not allow fine grained control over memory +allocation and is deprecated. + +4.35 KVM_SET_TSS_ADDR + +Capability: KVM_CAP_SET_TSS_ADDR +Architectures: x86 +Type: vm ioctl +Parameters: unsigned long tss_address (in) +Returns: 0 on success, -1 on error + +This ioctl defines the physical address of a three-page region in the guest +physical address space. The region must be within the first 4GB of the +guest physical address space and must not conflict with any memory slot +or any mmio address. The guest may malfunction if it accesses this memory +region. + +This ioctl is required on Intel-based hosts. This is needed on Intel hardware +because of a quirk in the virtualization implementation (see the internals +documentation when it pops into existence). + +4.36 KVM_ENABLE_CAP + +Capability: KVM_CAP_ENABLE_CAP +Architectures: ppc +Type: vcpu ioctl +Parameters: struct kvm_enable_cap (in) +Returns: 0 on success; -1 on error + ++Not all extensions are enabled by default. Using this ioctl the application +can enable an extension, making it available to the guest. + +On systems that do not support this ioctl, it always fails. On systems that +do support it, it only works for extensions that are supported for enablement. + +To check if a capability can be enabled, the KVM_CHECK_EXTENSION ioctl should +be used. + +struct kvm_enable_cap { + /* in */ + __u32 cap; + +The capability that is supposed to get enabled. + + __u32 flags; + +A bitfield indicating future enhancements. Has to be 0 for now. + + __u64 args[4]; + +Arguments for enabling a feature. If a feature needs initial values to +function properly, this is the place to put them. + + __u8 pad[64]; +}; + +4.37 KVM_GET_MP_STATE + +Capability: KVM_CAP_MP_STATE +Architectures: x86, ia64 +Type: vcpu ioctl +Parameters: struct kvm_mp_state (out) +Returns: 0 on success; -1 on error + +struct kvm_mp_state { + __u32 mp_state; +}; + +Returns the vcpu's current "multiprocessing state" (though also valid on +uniprocessor guests). + +Possible values are: + + - KVM_MP_STATE_RUNNABLE: the vcpu is currently running + - KVM_MP_STATE_UNINITIALIZED: the vcpu is an application processor (AP) + which has not yet received an INIT signal + - KVM_MP_STATE_INIT_RECEIVED: the vcpu has received an INIT signal, and is + now ready for a SIPI + - KVM_MP_STATE_HALTED: the vcpu has executed a HLT instruction and + is waiting for an interrupt + - KVM_MP_STATE_SIPI_RECEIVED: the vcpu has just received a SIPI (vector + accesible via KVM_GET_VCPU_EVENTS) + +This ioctl is only useful after KVM_CREATE_IRQCHIP. Without an in-kernel +irqchip, the multiprocessing state must be maintained by userspace. + +4.38 KVM_SET_MP_STATE + +Capability: KVM_CAP_MP_STATE +Architectures: x86, ia64 +Type: vcpu ioctl +Parameters: struct kvm_mp_state (in) +Returns: 0 on success; -1 on error + +Sets the vcpu's current "multiprocessing state"; see KVM_GET_MP_STATE for +arguments. + +This ioctl is only useful after KVM_CREATE_IRQCHIP. Without an in-kernel +irqchip, the multiprocessing state must be maintained by userspace. 5. The kvm_run structure @@ -820,6 +1002,13 @@ executed a memory-mapped I/O instruction which could not be satisfied by kvm. The 'data' member contains the written data if 'is_write' is true, and should be filled by application code otherwise. +NOTE: For KVM_EXIT_IO, KVM_EXIT_MMIO and KVM_EXIT_OSI, the corresponding +operations are complete (and guest state is consistent) only after userspace +has re-entered the kernel with KVM_RUN. The kernel side will first finish +incomplete operations and then check for pending signals. Userspace +can re-enter the guest with an unmasked signal pending to complete +pending operations. + /* KVM_EXIT_HYPERCALL */ struct { __u64 nr; @@ -829,7 +1018,9 @@ true, and should be filled by application code otherwise. __u32 pad; } hypercall; -Unused. +Unused. This was once used for 'hypercall to userspace'. To implement +such functionality, use KVM_EXIT_IO (x86) or KVM_EXIT_MMIO (all except s390). +Note KVM_EXIT_IO is significantly faster than KVM_EXIT_MMIO. /* KVM_EXIT_TPR_ACCESS */ struct { @@ -870,6 +1061,19 @@ s390 specific. powerpc specific. + /* KVM_EXIT_OSI */ + struct { + __u64 gprs[32]; + } osi; + +MOL uses a special hypercall interface it calls 'OSI'. To enable it, we catch +hypercalls and exit with this exit struct that contains all the guest gprs. + +If exit_reason is KVM_EXIT_OSI, then the vcpu has triggered such a hypercall. +Userspace can now handle the hypercall and when it's done modify the gprs as +necessary. Upon guest entry all guest GPRs will then be replaced by the values +in this struct. + /* Fix the size of the union. */ char padding[256]; }; diff --git a/Documentation/kvm/cpuid.txt b/Documentation/kvm/cpuid.txt new file mode 100644 index 000000000000..14a12ea92b7f --- /dev/null +++ b/Documentation/kvm/cpuid.txt @@ -0,0 +1,42 @@ +KVM CPUID bits +Glauber Costa <glommer@redhat.com>, Red Hat Inc, 2010 +===================================================== + +A guest running on a kvm host, can check some of its features using +cpuid. This is not always guaranteed to work, since userspace can +mask-out some, or even all KVM-related cpuid features before launching +a guest. + +KVM cpuid functions are: + +function: KVM_CPUID_SIGNATURE (0x40000000) +returns : eax = 0, + ebx = 0x4b4d564b, + ecx = 0x564b4d56, + edx = 0x4d. +Note that this value in ebx, ecx and edx corresponds to the string "KVMKVMKVM". +This function queries the presence of KVM cpuid leafs. + + +function: define KVM_CPUID_FEATURES (0x40000001) +returns : ebx, ecx, edx = 0 + eax = and OR'ed group of (1 << flag), where each flags is: + + +flag || value || meaning +============================================================================= +KVM_FEATURE_CLOCKSOURCE || 0 || kvmclock available at msrs + || || 0x11 and 0x12. +------------------------------------------------------------------------------ +KVM_FEATURE_NOP_IO_DELAY || 1 || not necessary to perform delays + || || on PIO operations. +------------------------------------------------------------------------------ +KVM_FEATURE_MMU_OP || 2 || deprecated. +------------------------------------------------------------------------------ +KVM_FEATURE_CLOCKSOURCE2 || 3 || kvmclock available at msrs + || || 0x4b564d00 and 0x4b564d01 +------------------------------------------------------------------------------ +KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side + || || per-cpu warps are expected in + || || kvmclock. +------------------------------------------------------------------------------ diff --git a/Documentation/kvm/mmu.txt b/Documentation/kvm/mmu.txt new file mode 100644 index 000000000000..aaed6ab9d7ab --- /dev/null +++ b/Documentation/kvm/mmu.txt @@ -0,0 +1,304 @@ +The x86 kvm shadow mmu +====================== + +The mmu (in arch/x86/kvm, files mmu.[ch] and paging_tmpl.h) is responsible +for presenting a standard x86 mmu to the guest, while translating guest +physical addresses to host physical addresses. + +The mmu code attempts to satisfy the following requirements: + +- correctness: the guest should not be able to determine that it is running + on an emulated mmu except for timing (we attempt to comply + with the specification, not emulate the characteristics of + a particular implementation such as tlb size) +- security: the guest must not be able to touch host memory not assigned + to it +- performance: minimize the performance penalty imposed by the mmu +- scaling: need to scale to large memory and large vcpu guests +- hardware: support the full range of x86 virtualization hardware +- integration: Linux memory management code must be in control of guest memory + so that swapping, page migration, page merging, transparent + hugepages, and similar features work without change +- dirty tracking: report writes to guest memory to enable live migration + and framebuffer-based displays +- footprint: keep the amount of pinned kernel memory low (most memory + should be shrinkable) +- reliablity: avoid multipage or GFP_ATOMIC allocations + +Acronyms +======== + +pfn host page frame number +hpa host physical address +hva host virtual address +gfn guest frame number +gpa guest physical address +gva guest virtual address +ngpa nested guest physical address +ngva nested guest virtual address +pte page table entry (used also to refer generically to paging structure + entries) +gpte guest pte (referring to gfns) +spte shadow pte (referring to pfns) +tdp two dimensional paging (vendor neutral term for NPT and EPT) + +Virtual and real hardware supported +=================================== + +The mmu supports first-generation mmu hardware, which allows an atomic switch +of the current paging mode and cr3 during guest entry, as well as +two-dimensional paging (AMD's NPT and Intel's EPT). The emulated hardware +it exposes is the traditional 2/3/4 level x86 mmu, with support for global +pages, pae, pse, pse36, cr0.wp, and 1GB pages. Work is in progress to support +exposing NPT capable hardware on NPT capable hosts. + +Translation +=========== + +The primary job of the mmu is to program the processor's mmu to translate +addresses for the guest. Different translations are required at different +times: + +- when guest paging is disabled, we translate guest physical addresses to + host physical addresses (gpa->hpa) +- when guest paging is enabled, we translate guest virtual addresses, to + guest physical addresses, to host physical addresses (gva->gpa->hpa) +- when the guest launches a guest of its own, we translate nested guest + virtual addresses, to nested guest physical addresses, to guest physical + addresses, to host physical addresses (ngva->ngpa->gpa->hpa) + +The primary challenge is to encode between 1 and 3 translations into hardware +that support only 1 (traditional) and 2 (tdp) translations. When the +number of required translations matches the hardware, the mmu operates in +direct mode; otherwise it operates in shadow mode (see below). + +Memory +====== + +Guest memory (gpa) is part of the user address space of the process that is +using kvm. Userspace defines the translation between guest addresses and user +addresses (gpa->hva); note that two gpas may alias to the same gva, but not +vice versa. + +These gvas may be backed using any method available to the host: anonymous +memory, file backed memory, and device memory. Memory might be paged by the +host at any time. + +Events +====== + +The mmu is driven by events, some from the guest, some from the host. + +Guest generated events: +- writes to control registers (especially cr3) +- invlpg/invlpga instruction execution +- access to missing or protected translations + +Host generated events: +- changes in the gpa->hpa translation (either through gpa->hva changes or + through hva->hpa changes) +- memory pressure (the shrinker) + +Shadow pages +============ + +The principal data structure is the shadow page, 'struct kvm_mmu_page'. A +shadow page contains 512 sptes, which can be either leaf or nonleaf sptes. A +shadow page may contain a mix of leaf and nonleaf sptes. + +A nonleaf spte allows the hardware mmu to reach the leaf pages and +is not related to a translation directly. It points to other shadow pages. + +A leaf spte corresponds to either one or two translations encoded into +one paging structure entry. These are always the lowest level of the +translation stack, with optional higher level translations left to NPT/EPT. +Leaf ptes point at guest pages. + +The following table shows translations encoded by leaf ptes, with higher-level +translations in parentheses: + + Non-nested guests: + nonpaging: gpa->hpa + paging: gva->gpa->hpa + paging, tdp: (gva->)gpa->hpa + Nested guests: + non-tdp: ngva->gpa->hpa (*) + tdp: (ngva->)ngpa->gpa->hpa + +(*) the guest hypervisor will encode the ngva->gpa translation into its page + tables if npt is not present + +Shadow pages contain the following information: + role.level: + The level in the shadow paging hierarchy that this shadow page belongs to. + 1=4k sptes, 2=2M sptes, 3=1G sptes, etc. + role.direct: + If set, leaf sptes reachable from this page are for a linear range. + Examples include real mode translation, large guest pages backed by small + host pages, and gpa->hpa translations when NPT or EPT is active. + The linear range starts at (gfn << PAGE_SHIFT) and its size is determined + by role.level (2MB for first level, 1GB for second level, 0.5TB for third + level, 256TB for fourth level) + If clear, this page corresponds to a guest page table denoted by the gfn + field. + role.quadrant: + When role.cr4_pae=0, the guest uses 32-bit gptes while the host uses 64-bit + sptes. That means a guest page table contains more ptes than the host, + so multiple shadow pages are needed to shadow one guest page. + For first-level shadow pages, role.quadrant can be 0 or 1 and denotes the + first or second 512-gpte block in the guest page table. For second-level + page tables, each 32-bit gpte is converted to two 64-bit sptes + (since each first-level guest page is shadowed by two first-level + shadow pages) so role.quadrant takes values in the range 0..3. Each + quadrant maps 1GB virtual address space. + role.access: + Inherited guest access permissions in the form uwx. Note execute + permission is positive, not negative. + role.invalid: + The page is invalid and should not be used. It is a root page that is + currently pinned (by a cpu hardware register pointing to it); once it is + unpinned it will be destroyed. + role.cr4_pae: + Contains the value of cr4.pae for which the page is valid (e.g. whether + 32-bit or 64-bit gptes are in use). + role.cr4_nxe: + Contains the value of efer.nxe for which the page is valid. + role.cr0_wp: + Contains the value of cr0.wp for which the page is valid. + gfn: + Either the guest page table containing the translations shadowed by this + page, or the base page frame for linear translations. See role.direct. + spt: + A pageful of 64-bit sptes containing the translations for this page. + Accessed by both kvm and hardware. + The page pointed to by spt will have its page->private pointing back + at the shadow page structure. + sptes in spt point either at guest pages, or at lower-level shadow pages. + Specifically, if sp1 and sp2 are shadow pages, then sp1->spt[n] may point + at __pa(sp2->spt). sp2 will point back at sp1 through parent_pte. + The spt array forms a DAG structure with the shadow page as a node, and + guest pages as leaves. + gfns: + An array of 512 guest frame numbers, one for each present pte. Used to + perform a reverse map from a pte to a gfn. + slot_bitmap: + A bitmap containing one bit per memory slot. If the page contains a pte + mapping a page from memory slot n, then bit n of slot_bitmap will be set + (if a page is aliased among several slots, then it is not guaranteed that + all slots will be marked). + Used during dirty logging to avoid scanning a shadow page if none if its + pages need tracking. + root_count: + A counter keeping track of how many hardware registers (guest cr3 or + pdptrs) are now pointing at the page. While this counter is nonzero, the + page cannot be destroyed. See role.invalid. + multimapped: + Whether there exist multiple sptes pointing at this page. + parent_pte/parent_ptes: + If multimapped is zero, parent_pte points at the single spte that points at + this page's spt. Otherwise, parent_ptes points at a data structure + with a list of parent_ptes. + unsync: + If true, then the translations in this page may not match the guest's + translation. This is equivalent to the state of the tlb when a pte is + changed but before the tlb entry is flushed. Accordingly, unsync ptes + are synchronized when the guest executes invlpg or flushes its tlb by + other means. Valid for leaf pages. + unsync_children: + How many sptes in the page point at pages that are unsync (or have + unsynchronized children). + unsync_child_bitmap: + A bitmap indicating which sptes in spt point (directly or indirectly) at + pages that may be unsynchronized. Used to quickly locate all unsychronized + pages reachable from a given page. + +Reverse map +=========== + +The mmu maintains a reverse mapping whereby all ptes mapping a page can be +reached given its gfn. This is used, for example, when swapping out a page. + +Synchronized and unsynchronized pages +===================================== + +The guest uses two events to synchronize its tlb and page tables: tlb flushes +and page invalidations (invlpg). + +A tlb flush means that we need to synchronize all sptes reachable from the +guest's cr3. This is expensive, so we keep all guest page tables write +protected, and synchronize sptes to gptes when a gpte is written. + +A special case is when a guest page table is reachable from the current +guest cr3. In this case, the guest is obliged to issue an invlpg instruction +before using the translation. We take advantage of that by removing write +protection from the guest page, and allowing the guest to modify it freely. +We synchronize modified gptes when the guest invokes invlpg. This reduces +the amount of emulation we have to do when the guest modifies multiple gptes, +or when the a guest page is no longer used as a page table and is used for +random guest data. + +As a side effect we have to resynchronize all reachable unsynchronized shadow +pages on a tlb flush. + + +Reaction to events +================== + +- guest page fault (or npt page fault, or ept violation) + +This is the most complicated event. The cause of a page fault can be: + + - a true guest fault (the guest translation won't allow the access) (*) + - access to a missing translation + - access to a protected translation + - when logging dirty pages, memory is write protected + - synchronized shadow pages are write protected (*) + - access to untranslatable memory (mmio) + + (*) not applicable in direct mode + +Handling a page fault is performed as follows: + + - if needed, walk the guest page tables to determine the guest translation + (gva->gpa or ngpa->gpa) + - if permissions are insufficient, reflect the fault back to the guest + - determine the host page + - if this is an mmio request, there is no host page; call the emulator + to emulate the instruction instead + - walk the shadow page table to find the spte for the translation, + instantiating missing intermediate page tables as necessary + - try to unsynchronize the page + - if successful, we can let the guest continue and modify the gpte + - emulate the instruction + - if failed, unshadow the page and let the guest continue + - update any translations that were modified by the instruction + +invlpg handling: + + - walk the shadow page hierarchy and drop affected translations + - try to reinstantiate the indicated translation in the hope that the + guest will use it in the near future + +Guest control register updates: + +- mov to cr3 + - look up new shadow roots + - synchronize newly reachable shadow pages + +- mov to cr0/cr4/efer + - set up mmu context for new paging mode + - look up new shadow roots + - synchronize newly reachable shadow pages + +Host translation updates: + + - mmu notifier called with updated hva + - look up affected sptes through reverse map + - drop (or update) translations + +Further reading +=============== + +- NPT presentation from KVM Forum 2008 + http://www.linux-kvm.org/wiki/images/c/c8/KvmForum2008%24kdf2008_21.pdf + |