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KVM: arm64: Add documentation for KVM_EXIT_ARM_LDST64B

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Add a bit of documentation for KVM_EXIT_ARM_LDST64B so that userspace
knows what to expect.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Oliver Upton <oupton@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Signed-off-by: Zhou Wang <wangzhou1@hisilicon.com>
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Marc Zyngier
2026-01-19 10:29:23 +08:00
committed by Will Deacon
parent f174a9ffcd
commit 902eebac8f
1 changed files with 36 additions and 7 deletions
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43
Documentation/virt/kvm/api.rst
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@@ -1303,12 +1303,13 @@ userspace, for example because of missing instruction syndrome decode
information or because there is no device mapped at the accessed IPA, then
userspace can ask the kernel to inject an external abort using the address
from the exiting fault on the VCPU. It is a programming error to set
ext_dabt_pending after an exit which was not either KVM_EXIT_MMIO or
KVM_EXIT_ARM_NISV. This feature is only available if the system supports
KVM_CAP_ARM_INJECT_EXT_DABT. This is a helper which provides commonality in
how userspace reports accesses for the above cases to guests, across different
userspace implementations. Nevertheless, userspace can still emulate all Arm
exceptions by manipulating individual registers using the KVM_SET_ONE_REG API.
ext_dabt_pending after an exit which was not either KVM_EXIT_MMIO,
KVM_EXIT_ARM_NISV, or KVM_EXIT_ARM_LDST64B. This feature is only available if
the system supports KVM_CAP_ARM_INJECT_EXT_DABT. This is a helper which
provides commonality in how userspace reports accesses for the above cases to
guests, across different userspace implementations. Nevertheless, userspace
can still emulate all Arm exceptions by manipulating individual registers
using the KVM_SET_ONE_REG API.
See KVM_GET_VCPU_EVENTS for the data structure.
@@ -7050,12 +7051,14 @@ in send_page or recv a buffer to recv_page).
::
/* KVM_EXIT_ARM_NISV */
/* KVM_EXIT_ARM_NISV / KVM_EXIT_ARM_LDST64B */
struct {
__u64 esr_iss;
__u64 fault_ipa;
} arm_nisv;
- KVM_EXIT_ARM_NISV:
Used on arm64 systems. If a guest accesses memory not in a memslot,
KVM will typically return to userspace and ask it to do MMIO emulation on its
behalf. However, for certain classes of instructions, no instruction decode
@@ -7089,6 +7092,32 @@ Note that although KVM_CAP_ARM_NISV_TO_USER will be reported if
queried outside of a protected VM context, the feature will not be
exposed if queried on a protected VM file descriptor.
- KVM_EXIT_ARM_LDST64B:
Used on arm64 systems. When a guest using a LD64B, ST64B, ST64BV, ST64BV0,
outside of a memslot, KVM will return to userspace with KVM_EXIT_ARM_LDST64B,
exposing the relevant ESR_EL2 information and faulting IPA, similarly to
KVM_EXIT_ARM_NISV.
Userspace is supposed to fully emulate the instructions, which includes:
- fetch of the operands for a store, including ACCDATA_EL1 in the case
of a ST64BV0 instruction
- deal with the endianness if the guest is big-endian
- emulate the access, including the delivery of an exception if the
access didn't succeed
- provide a return value in the case of ST64BV/ST64BV0
- return the data in the case of a load
- increment PC if the instruction was successfully executed
Note that there is no expectation of performance for this emulation, as it
involves a large number of interaction with the guest state. It is, however,
expected that the instruction's semantics are preserved, specially the
single-copy atomicity property of the 64 byte access.
This exit reason must be handled if userspace sets ID_AA64ISAR1_EL1.LS64 to a
non-zero value, indicating that FEAT_LS64* is enabled.
::
/* KVM_EXIT_X86_RDMSR / KVM_EXIT_X86_WRMSR */