diff mbox series

[v5,01/10] KVM: arm64: Document PV-time interface

Message ID 20191002145037.51630-2-steven.price@arm.com
State New, archived
Headers show
Series arm64: Stolen time support | expand

Commit Message

Steven Price Oct. 2, 2019, 2:50 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.txt   | 65 +++++++++++++++++++++++++
 Documentation/virt/kvm/devices/vcpu.txt | 14 ++++++
 2 files changed, 79 insertions(+)
 create mode 100644 Documentation/virt/kvm/arm/pvtime.txt

Comments

Andrew Jones Oct. 3, 2019, 12:19 p.m. UTC | #1
On Wed, Oct 02, 2019 at 03:50:28PM +0100, Steven Price wrote:
> 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.txt   | 65 +++++++++++++++++++++++++
>  Documentation/virt/kvm/devices/vcpu.txt | 14 ++++++
>  2 files changed, 79 insertions(+)
>  create mode 100644 Documentation/virt/kvm/arm/pvtime.txt
> 
> diff --git a/Documentation/virt/kvm/arm/pvtime.txt b/Documentation/virt/kvm/arm/pvtime.txt
> new file mode 100644
> index 000000000000..fa15c12eec91
> --- /dev/null
> +++ b/Documentation/virt/kvm/arm/pvtime.txt

Maybe use .rst instead of .txt?

> @@ -0,0 +1,65 @@
> +Paravirtualized time support for arm64
> +======================================
> +
> +Arm specification DEN0057/A defined a standard for paravirtualised time

s/defined/defines/ ?

> +support for AArch64 guests:
> +
> +https://developer.arm.com/docs/den0057/a
> +
> +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_FEATURES 0xC5000020

The spec calls this PV_TIME_FEATURES.

> +PV_TIME_ST  0xC5000022

This is 0xC5000021 in the spec.

> +
> +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.
> +
> +PV_FEATURES
> +    Function ID:  (uint32)  : 0xC5000020
> +    PV_func_id:   (uint32)  : The function to query for support.
> +                              Currently only PV_TIME_ST is supported.

The spec calls this PV_call_id, but maybe PV_func_id would have been better.

> +    Return value: (int32)   : NOT_SUPPORTED (-1) or SUCCESS (0) if the relevant
> +                              PV-time feature is supported by the hypervisor.

This is an int64 in the spec.

> +
> +PV_TIME_ST
> +    Function ID:  (uint32)  : 0xC5000022
> +    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 0.1

The spec version is 1.0 and Table 1 says "For implementations compliant
with this revision of the specification...". So I think this description
should be "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.
> +
> +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
> +section "3. GROUP: KVM_ARM_VCPU_PVTIME_CTRL".
> +
> 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
>  VCPUs.
> +
> +3. GROUP: KVM_ARM_VCPU_PVTIME_CTRL
> +Architectures: ARM64
> +
> +3.1 ATTRIBUTE: KVM_ARM_VCPU_PVTIME_IPA
> +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.
> -- 
> 2.20.1
>

Thanks,
drew
Steven Price Oct. 4, 2019, 9 a.m. UTC | #2
On 03/10/2019 13:19, Andrew Jones wrote:
> On Wed, Oct 02, 2019 at 03:50:28PM +0100, Steven Price wrote:
>> 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.txt   | 65 +++++++++++++++++++++++++
>>  Documentation/virt/kvm/devices/vcpu.txt | 14 ++++++
>>  2 files changed, 79 insertions(+)
>>  create mode 100644 Documentation/virt/kvm/arm/pvtime.txt
>>
>> diff --git a/Documentation/virt/kvm/arm/pvtime.txt b/Documentation/virt/kvm/arm/pvtime.txt
>> new file mode 100644
>> index 000000000000..fa15c12eec91
>> --- /dev/null
>> +++ b/Documentation/virt/kvm/arm/pvtime.txt
> 
> Maybe use .rst instead of .txt?

Fair point - I guess .rst is the way of the future!

>> @@ -0,0 +1,65 @@
>> +Paravirtualized time support for arm64
>> +======================================
>> +
>> +Arm specification DEN0057/A defined a standard for paravirtualised time
> 
> s/defined/defines/ ?
> 
>> +support for AArch64 guests:
>> +
>> +https://developer.arm.com/docs/den0057/a
>> +
>> +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_FEATURES 0xC5000020
> 
> The spec calls this PV_TIME_FEATURES.
> 
>> +PV_TIME_ST  0xC5000022
> 
> This is 0xC5000021 in the spec.

This is somewhat embarrassing. Apparently when I was reviewing the new
specification I didn't notice these (subtle) changes. Thanks for
pointing it out to me! I'll update the code to match.

>> +
>> +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.
>> +
>> +PV_FEATURES
>> +    Function ID:  (uint32)  : 0xC5000020
>> +    PV_func_id:   (uint32)  : The function to query for support.
>> +                              Currently only PV_TIME_ST is supported.
> 
> The spec calls this PV_call_id, but maybe PV_func_id would have been better.

I guess they are generally called "hypercalls" not "hyperfunctions" - so
I'll match the spec here.

>> +    Return value: (int32)   : NOT_SUPPORTED (-1) or SUCCESS (0) if the relevant
>> +                              PV-time feature is supported by the hypervisor.
> 
> This is an int64 in the spec.

True - although the values easily fit in int32 too! But I'll update to
be consistent with the spec.

>> +
>> +PV_TIME_ST
>> +    Function ID:  (uint32)  : 0xC5000022
>> +    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 0.1
> 
> The spec version is 1.0 and Table 1 says "For implementations compliant
> with this revision of the specification...". So I think this description
> should be "Must be 0 for version 1.0".

Will update.

Thanks,

Steve

>> +  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.
>> +
>> +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
>> +section "3. GROUP: KVM_ARM_VCPU_PVTIME_CTRL".
>> +
>> 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
>>  VCPUs.
>> +
>> +3. GROUP: KVM_ARM_VCPU_PVTIME_CTRL
>> +Architectures: ARM64
>> +
>> +3.1 ATTRIBUTE: KVM_ARM_VCPU_PVTIME_IPA
>> +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.
>> -- 
>> 2.20.1
>>
> 
> Thanks,
> drew 
>
diff mbox series

Patch

diff --git a/Documentation/virt/kvm/arm/pvtime.txt b/Documentation/virt/kvm/arm/pvtime.txt
new file mode 100644
index 000000000000..fa15c12eec91
--- /dev/null
+++ b/Documentation/virt/kvm/arm/pvtime.txt
@@ -0,0 +1,65 @@ 
+Paravirtualized time support for arm64
+======================================
+
+Arm specification DEN0057/A defined a standard for paravirtualised time
+support for AArch64 guests:
+
+https://developer.arm.com/docs/den0057/a
+
+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_FEATURES 0xC5000020
+PV_TIME_ST  0xC5000022
+
+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.
+
+PV_FEATURES
+    Function ID:  (uint32)  : 0xC5000020
+    PV_func_id:   (uint32)  : The function to query for support.
+                              Currently only PV_TIME_ST is supported.
+    Return value: (int32)   : NOT_SUPPORTED (-1) or SUCCESS (0) if the relevant
+                              PV-time feature is supported by the hypervisor.
+
+PV_TIME_ST
+    Function ID:  (uint32)  : 0xC5000022
+    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 0.1
+  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.
+
+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
+section "3. GROUP: KVM_ARM_VCPU_PVTIME_CTRL".
+
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
 VCPUs.
+
+3. GROUP: KVM_ARM_VCPU_PVTIME_CTRL
+Architectures: ARM64
+
+3.1 ATTRIBUTE: KVM_ARM_VCPU_PVTIME_IPA
+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.