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955d8dc3ee
Emulate the HYPCALL instruction added in the VZ ASE and used by the MIPS paravirtualised guest support that is already merged. The new hypcall.c handles arguments and the return value. No actual hypercalls are yet supported, but this still allows us to safely step over hypercalls and set an error code in the return value for forward compatibility. Non-zero HYPCALL codes are not handled. We also document the hypercall ABI which asm/kvm_para.h uses. Signed-off-by: James Hogan <james.hogan@imgtec.com> Acked-by: Ralf Baechle <ralf@linux-mips.org> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: "Radim Krčmář" <rkrcmar@redhat.com> Cc: Andreas Herrmann <andreas.herrmann@caviumnetworks.com> Cc: David Daney <david.daney@cavium.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: linux-mips@linux-mips.org Cc: kvm@vger.kernel.org Cc: linux-doc@vger.kernel.org
124 lines
4.2 KiB
Plaintext
124 lines
4.2 KiB
Plaintext
Linux KVM Hypercall:
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===================
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X86:
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KVM Hypercalls have a three-byte sequence of either the vmcall or the vmmcall
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instruction. The hypervisor can replace it with instructions that are
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guaranteed to be supported.
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Up to four arguments may be passed in rbx, rcx, rdx, and rsi respectively.
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The hypercall number should be placed in rax and the return value will be
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placed in rax. No other registers will be clobbered unless explicitly stated
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by the particular hypercall.
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S390:
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R2-R7 are used for parameters 1-6. In addition, R1 is used for hypercall
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number. The return value is written to R2.
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S390 uses diagnose instruction as hypercall (0x500) along with hypercall
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number in R1.
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For further information on the S390 diagnose call as supported by KVM,
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refer to Documentation/virtual/kvm/s390-diag.txt.
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PowerPC:
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It uses R3-R10 and hypercall number in R11. R4-R11 are used as output registers.
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Return value is placed in R3.
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KVM hypercalls uses 4 byte opcode, that are patched with 'hypercall-instructions'
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property inside the device tree's /hypervisor node.
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For more information refer to Documentation/virtual/kvm/ppc-pv.txt
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MIPS:
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KVM hypercalls use the HYPCALL instruction with code 0 and the hypercall
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number in $2 (v0). Up to four arguments may be placed in $4-$7 (a0-a3) and
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the return value is placed in $2 (v0).
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KVM Hypercalls Documentation
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===========================
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The template for each hypercall is:
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1. Hypercall name.
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2. Architecture(s)
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3. Status (deprecated, obsolete, active)
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4. Purpose
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1. KVM_HC_VAPIC_POLL_IRQ
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------------------------
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Architecture: x86
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Status: active
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Purpose: Trigger guest exit so that the host can check for pending
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interrupts on reentry.
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2. KVM_HC_MMU_OP
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------------------------
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Architecture: x86
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Status: deprecated.
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Purpose: Support MMU operations such as writing to PTE,
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flushing TLB, release PT.
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3. KVM_HC_FEATURES
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------------------------
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Architecture: PPC
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Status: active
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Purpose: Expose hypercall availability to the guest. On x86 platforms, cpuid
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used to enumerate which hypercalls are available. On PPC, either device tree
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based lookup ( which is also what EPAPR dictates) OR KVM specific enumeration
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mechanism (which is this hypercall) can be used.
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4. KVM_HC_PPC_MAP_MAGIC_PAGE
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------------------------
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Architecture: PPC
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Status: active
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Purpose: To enable communication between the hypervisor and guest there is a
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shared page that contains parts of supervisor visible register state.
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The guest can map this shared page to access its supervisor register through
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memory using this hypercall.
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5. KVM_HC_KICK_CPU
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------------------------
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Architecture: x86
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Status: active
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Purpose: Hypercall used to wakeup a vcpu from HLT state
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Usage example : A vcpu of a paravirtualized guest that is busywaiting in guest
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kernel mode for an event to occur (ex: a spinlock to become available) can
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execute HLT instruction once it has busy-waited for more than a threshold
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time-interval. Execution of HLT instruction would cause the hypervisor to put
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the vcpu to sleep until occurrence of an appropriate event. Another vcpu of the
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same guest can wakeup the sleeping vcpu by issuing KVM_HC_KICK_CPU hypercall,
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specifying APIC ID (a1) of the vcpu to be woken up. An additional argument (a0)
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is used in the hypercall for future use.
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6. KVM_HC_CLOCK_PAIRING
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------------------------
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Architecture: x86
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Status: active
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Purpose: Hypercall used to synchronize host and guest clocks.
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Usage:
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a0: guest physical address where host copies
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"struct kvm_clock_offset" structure.
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a1: clock_type, ATM only KVM_CLOCK_PAIRING_WALLCLOCK (0)
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is supported (corresponding to the host's CLOCK_REALTIME clock).
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struct kvm_clock_pairing {
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__s64 sec;
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__s64 nsec;
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__u64 tsc;
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__u32 flags;
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__u32 pad[9];
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};
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Where:
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* sec: seconds from clock_type clock.
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* nsec: nanoseconds from clock_type clock.
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* tsc: guest TSC value used to calculate sec/nsec pair
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* flags: flags, unused (0) at the moment.
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The hypercall lets a guest compute a precise timestamp across
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host and guest. The guest can use the returned TSC value to
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compute the CLOCK_REALTIME for its clock, at the same instant.
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Returns KVM_EOPNOTSUPP if the host does not use TSC clocksource,
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or if clock type is different than KVM_CLOCK_PAIRING_WALLCLOCK.
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