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[v6,01/10] KVM: arm64: Document PV-time interface

Message ID 20191011125930.40834-2-steven.price@arm.com (mailing list archive)
State New, archived
Headers show
Series arm64: Stolen time support | expand

Commit Message

Steven Price Oct. 11, 2019, 12:59 p.m. UTC
Introduce a paravirtualization interface for KVM/arm64 based on the
"Arm Paravirtualized Time for Arm-Base Systems" specification DEN 0057A.

This only adds the details about "Stolen Time" as the details of "Live
Physical Time" have not been fully agreed.

User space can specify a reserved area of memory for the guest and
inform KVM to populate the memory with information on time that the host
kernel has stolen from the guest.

A hypercall interface is provided for the guest to interrogate the
hypervisor's support for this interface and the location of the shared
memory structures.

Signed-off-by: Steven Price <steven.price@arm.com>
 Documentation/virt/kvm/arm/pvtime.rst   | 77 +++++++++++++++++++++++++
 Documentation/virt/kvm/devices/vcpu.txt | 14 +++++
 2 files changed, 91 insertions(+)
 create mode 100644 Documentation/virt/kvm/arm/pvtime.rst
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diff --git a/Documentation/virt/kvm/arm/pvtime.rst b/Documentation/virt/kvm/arm/pvtime.rst
new file mode 100644
index 000000000000..de949933ec78
--- /dev/null
+++ b/Documentation/virt/kvm/arm/pvtime.rst
@@ -0,0 +1,77 @@ 
+.. SPDX-License-Identifier: GPL-2.0
+Paravirtualized time support for arm64
+Arm specification DEN0057/A defines a standard for paravirtualised time
+support for AArch64 guests:
+KVM/arm64 implements the stolen time part of this specification by providing
+some hypervisor service calls to support a paravirtualized guest obtaining a
+view of the amount of time stolen from its execution.
+Two new SMCCC compatible hypercalls are defined:
+* PV_TIME_FEATURES: 0xC5000020
+* PV_TIME_ST:       0xC5000021
+These are only available in the SMC64/HVC64 calling convention as
+paravirtualized time is not available to 32 bit Arm guests. The existence of
+the PV_FEATURES hypercall should be probed using the SMCCC 1.1 ARCH_FEATURES
+mechanism before calling it.
+    ============= ========    ==========
+    Function ID:  (uint32)    0xC5000020
+    PV_call_id:   (uint32)    The function to query for support.
+                              Currently only PV_TIME_ST is supported.
+    Return value: (int64)     NOT_SUPPORTED (-1) or SUCCESS (0) if the relevant
+                              PV-time feature is supported by the hypervisor.
+    ============= ========    ==========
+    ============= ========    ==========
+    Function ID:  (uint32)    0xC5000021
+    Return value: (int64)     IPA of the stolen time data structure for this
+                              VCPU. On failure:
+                              NOT_SUPPORTED (-1)
+    ============= ========    ==========
+The IPA returned by PV_TIME_ST should be mapped by the guest as normal memory
+with inner and outer write back caching attributes, in the inner shareable
+domain. A total of 16 bytes from the IPA returned are guaranteed to be
+meaningfully filled by the hypervisor (see structure below).
+PV_TIME_ST returns the structure for the calling VCPU.
+Stolen Time
+The structure pointed to by the PV_TIME_ST hypercall is as follows:
+| Field       | Byte Length | Byte Offset | Description                |
+| Revision    |      4      |      0      | Must be 0 for version 1.0  |
+| Attributes  |      4      |      4      | Must be 0                  |
+| Stolen time |      8      |      8      | Stolen time in unsigned    |
+|             |             |             | nanoseconds indicating how |
+|             |             |             | much time this VCPU thread |
+|             |             |             | was involuntarily not      |
+|             |             |             | running on a physical CPU. |
+All values in the structure are stored little-endian.
+The structure will be updated by the hypervisor prior to scheduling a VCPU. It
+will be present within a reserved region of the normal memory given to the
+guest. The guest should not attempt to write into this memory. There is a
+structure per VCPU of the guest.
+For the user space interface see Documentation/virt/kvm/devices/vcpu.txt
diff --git a/Documentation/virt/kvm/devices/vcpu.txt b/Documentation/virt/kvm/devices/vcpu.txt
index 2b5dab16c4f2..6f3bd64a05b0 100644
--- a/Documentation/virt/kvm/devices/vcpu.txt
+++ b/Documentation/virt/kvm/devices/vcpu.txt
@@ -60,3 +60,17 @@  time to use the number provided for a given timer, overwriting any previously
 configured values on other VCPUs.  Userspace should configure the interrupt
 numbers on at least one VCPU after creating all VCPUs and before running any
+Architectures: ARM64
+Parameters: 64-bit base address
+Returns: -ENXIO:  Stolen time not implemented
+         -EEXIST: Base address already set for this VCPU
+         -EINVAL: Base address not 64 byte aligned
+Specifies the base address of the stolen time structure for this VCPU. The
+base address must be 64 byte aligned and exist within a valid guest memory
+region. See Documentation/virt/kvm/arm/pvtime.txt for more information
+including the layout of the stolen time structure.