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KVM: x86: KVM_CAP_SYNC_REGS

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This commit implements an enhanced x86 version of S390
KVM_CAP_SYNC_REGS functionality. KVM_CAP_SYNC_REGS "allow[s]
userspace to access certain guest registers without having
to call SET/GET_*REGS”. This reduces ioctl overhead which
is particularly important when userspace is making synchronous
guest state modifications (e.g. when emulating and/or intercepting
instructions).

Originally implemented upstream for the S390, the x86 differences
follow:
- userspace can select the register sets to be synchronized with kvm_run
using bit-flags in the kvm_valid_registers and kvm_dirty_registers
fields.
- vcpu_events is available in addition to the regs and sregs register
sets.

Signed-off-by: Ken Hofsass <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
[Removed wrapper around check for reserved kvm_valid_regs. - Radim]
Signed-off-by: Radim Krčmář <[email protected]>
This commit is contained in:
Ken Hofsass 2018-01-31 16:03:36 -08:00 • committed by Radim Krčmář
commit 01643c51bf
3 changed files with 145 additions and 16 deletions
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40
Documentation/virtual/kvm/api.txt
View file

@ -4110,6 +4110,46 @@ Once this is done the KVM_REG_MIPS_VEC_* and KVM_REG_MIPS_MSA_* registers can be
accessed, and the Config5.MSAEn bit is accessible via the KVM API and also from
the guest.
6.74 KVM_CAP_SYNC_REGS
Architectures: s390, x86
Target: s390: always enabled, x86: vcpu
Parameters: none
Returns: x86: KVM_CHECK_EXTENSION returns a bit-array indicating which register
sets are supported (bitfields defined in arch/x86/include/uapi/asm/kvm.h).
As described above in the kvm_sync_regs struct info in section 5 (kvm_run):
KVM_CAP_SYNC_REGS "allow[s] userspace to access certain guest registers
without having to call SET/GET_*REGS". This reduces overhead by eliminating
repeated ioctl calls for setting and/or getting register values. This is
particularly important when userspace is making synchronous guest state
modifications, e.g. when emulating and/or intercepting instructions in
userspace.
For s390 specifics, please refer to the source code.
For x86:
- the register sets to be copied out to kvm_run are selectable
by userspace (rather that all sets being copied out for every exit).
- vcpu_events are available in addition to regs and sregs.
For x86, the 'kvm_valid_regs' field of struct kvm_run is overloaded to
function as an input bit-array field set by userspace to indicate the
specific register sets to be copied out on the next exit.
To indicate when userspace has modified values that should be copied into
the vCPU, the all architecture bitarray field, 'kvm_dirty_regs' must be set.
This is done using the same bitflags as for the 'kvm_valid_regs' field.
If the dirty bit is not set, then the register set values will not be copied
into the vCPU even if they've been modified.
Unused bitfields in the bitarrays must be set to zero.
struct kvm_sync_regs {
struct kvm_regs regs;
struct kvm_sregs sregs;
struct kvm_vcpu_events events;
};
7. Capabilities that can be enabled on VMs
------------------------------------------