mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-24 21:24:00 +08:00
55dd00a73a
Add a hypercall to retrieve the host realtime clock and the TSC value used to calculate that clock read. Used to implement clock synchronization between host and guest. Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
119 lines
4.0 KiB
Plaintext
119 lines
4.0 KiB
Plaintext
Linux KVM Hypercall:
|
|
===================
|
|
X86:
|
|
KVM Hypercalls have a three-byte sequence of either the vmcall or the vmmcall
|
|
instruction. The hypervisor can replace it with instructions that are
|
|
guaranteed to be supported.
|
|
|
|
Up to four arguments may be passed in rbx, rcx, rdx, and rsi respectively.
|
|
The hypercall number should be placed in rax and the return value will be
|
|
placed in rax. No other registers will be clobbered unless explicitly stated
|
|
by the particular hypercall.
|
|
|
|
S390:
|
|
R2-R7 are used for parameters 1-6. In addition, R1 is used for hypercall
|
|
number. The return value is written to R2.
|
|
|
|
S390 uses diagnose instruction as hypercall (0x500) along with hypercall
|
|
number in R1.
|
|
|
|
For further information on the S390 diagnose call as supported by KVM,
|
|
refer to Documentation/virtual/kvm/s390-diag.txt.
|
|
|
|
PowerPC:
|
|
It uses R3-R10 and hypercall number in R11. R4-R11 are used as output registers.
|
|
Return value is placed in R3.
|
|
|
|
KVM hypercalls uses 4 byte opcode, that are patched with 'hypercall-instructions'
|
|
property inside the device tree's /hypervisor node.
|
|
For more information refer to Documentation/virtual/kvm/ppc-pv.txt
|
|
|
|
KVM Hypercalls Documentation
|
|
===========================
|
|
The template for each hypercall is:
|
|
1. Hypercall name.
|
|
2. Architecture(s)
|
|
3. Status (deprecated, obsolete, active)
|
|
4. Purpose
|
|
|
|
1. KVM_HC_VAPIC_POLL_IRQ
|
|
------------------------
|
|
Architecture: x86
|
|
Status: active
|
|
Purpose: Trigger guest exit so that the host can check for pending
|
|
interrupts on reentry.
|
|
|
|
2. KVM_HC_MMU_OP
|
|
------------------------
|
|
Architecture: x86
|
|
Status: deprecated.
|
|
Purpose: Support MMU operations such as writing to PTE,
|
|
flushing TLB, release PT.
|
|
|
|
3. KVM_HC_FEATURES
|
|
------------------------
|
|
Architecture: PPC
|
|
Status: active
|
|
Purpose: Expose hypercall availability to the guest. On x86 platforms, cpuid
|
|
used to enumerate which hypercalls are available. On PPC, either device tree
|
|
based lookup ( which is also what EPAPR dictates) OR KVM specific enumeration
|
|
mechanism (which is this hypercall) can be used.
|
|
|
|
4. KVM_HC_PPC_MAP_MAGIC_PAGE
|
|
------------------------
|
|
Architecture: PPC
|
|
Status: active
|
|
Purpose: To enable communication between the hypervisor and guest there is a
|
|
shared page that contains parts of supervisor visible register state.
|
|
The guest can map this shared page to access its supervisor register through
|
|
memory using this hypercall.
|
|
|
|
5. KVM_HC_KICK_CPU
|
|
------------------------
|
|
Architecture: x86
|
|
Status: active
|
|
Purpose: Hypercall used to wakeup a vcpu from HLT state
|
|
Usage example : A vcpu of a paravirtualized guest that is busywaiting in guest
|
|
kernel mode for an event to occur (ex: a spinlock to become available) can
|
|
execute HLT instruction once it has busy-waited for more than a threshold
|
|
time-interval. Execution of HLT instruction would cause the hypervisor to put
|
|
the vcpu to sleep until occurrence of an appropriate event. Another vcpu of the
|
|
same guest can wakeup the sleeping vcpu by issuing KVM_HC_KICK_CPU hypercall,
|
|
specifying APIC ID (a1) of the vcpu to be woken up. An additional argument (a0)
|
|
is used in the hypercall for future use.
|
|
|
|
|
|
6. KVM_HC_CLOCK_PAIRING
|
|
------------------------
|
|
Architecture: x86
|
|
Status: active
|
|
Purpose: Hypercall used to synchronize host and guest clocks.
|
|
Usage:
|
|
|
|
a0: guest physical address where host copies
|
|
"struct kvm_clock_offset" structure.
|
|
|
|
a1: clock_type, ATM only KVM_CLOCK_PAIRING_WALLCLOCK (0)
|
|
is supported (corresponding to the host's CLOCK_REALTIME clock).
|
|
|
|
struct kvm_clock_pairing {
|
|
__s64 sec;
|
|
__s64 nsec;
|
|
__u64 tsc;
|
|
__u32 flags;
|
|
__u32 pad[9];
|
|
};
|
|
|
|
Where:
|
|
* sec: seconds from clock_type clock.
|
|
* nsec: nanoseconds from clock_type clock.
|
|
* tsc: guest TSC value used to calculate sec/nsec pair
|
|
* flags: flags, unused (0) at the moment.
|
|
|
|
The hypercall lets a guest compute a precise timestamp across
|
|
host and guest. The guest can use the returned TSC value to
|
|
compute the CLOCK_REALTIME for its clock, at the same instant.
|
|
|
|
Returns KVM_EOPNOTSUPP if the host does not use TSC clocksource,
|
|
or if clock type is different than KVM_CLOCK_PAIRING_WALLCLOCK.
|