From: Steven Price <steven.price@arm.com>
To: Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>,
linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu
Cc: "Steven Price" <steven.price@arm.com>,
"Catalin Marinas" <catalin.marinas@arm.com>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <rkrcmar@redhat.com>,
"Russell King" <linux@armlinux.org.uk>,
"James Morse" <james.morse@arm.com>,
"Julien Thierry" <julien.thierry.kdev@gmail.com>,
"Suzuki K Pouloze" <suzuki.poulose@arm.com>,
"Mark Rutland" <mark.rutland@arm.com>,
kvm@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: [PATCH v2 1/9] KVM: arm64: Document PV-time interface
Date: Mon, 19 Aug 2019 15:04:28 +0100 [thread overview]
Message-ID: <20190819140436.12207-2-steven.price@arm.com> (raw)
In-Reply-To: <20190819140436.12207-1-steven.price@arm.com>
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 | 100 ++++++++++++++++++++++++++
1 file changed, 100 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..1ceb118694e7
--- /dev/null
+++ b/Documentation/virt/kvm/arm/pvtime.txt
@@ -0,0 +1,100 @@
+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) : Either PV_TIME_LPT or PV_TIME_ST
+ 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
+ (V)CPU. 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.
+
+User space interface
+====================
+
+User space can request that KVM provide the paravirtualized time interface to
+a guest by creating a KVM_DEV_TYPE_ARM_PV_TIME device, for example:
+
+ struct kvm_create_device pvtime_device = {
+ .type = KVM_DEV_TYPE_ARM_PV_TIME,
+ .attr = 0,
+ .flags = 0,
+ };
+
+ pvtime_fd = ioctl(vm_fd, KVM_CREATE_DEVICE, &pvtime_device);
+
+Creation of the device should be done after creating the vCPUs of the virtual
+machine.
+
+The IPA of the structures must be given to KVM. This is the base address
+of an array of stolen time structures (one for each VCPU). The base address
+must be page aligned. The size must be at least 64 * number of VCPUs and be a
+multiple of PAGE_SIZE.
+
+The memory for these structures should be added to the guest in the usual
+manner (e.g. using KVM_SET_USER_MEMORY_REGION).
+
+For example:
+
+ struct kvm_dev_arm_st_region region = {
+ .gpa = <IPA of guest base address>,
+ .size = <size in bytes>
+ };
+
+ struct kvm_device_attr st_base = {
+ .group = KVM_DEV_ARM_PV_TIME_PADDR,
+ .attr = KVM_DEV_ARM_PV_TIME_ST,
+ .addr = (u64)®ion
+ };
+
+ ioctl(pvtime_fd, KVM_SET_DEVICE_ATTR, &st_base);
--
2.20.1
next prev parent reply other threads:[~2019-08-19 14:04 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-19 14:04 [PATCH v2 0/9] arm64: Stolen time support Steven Price
2019-08-19 14:04 ` Steven Price [this message]
2019-08-19 14:04 ` [PATCH v2 2/9] KVM: arm/arm64: Factor out hypercall handling from PSCI code Steven Price
2019-08-19 14:04 ` [PATCH v2 3/9] KVM: arm64: Implement PV_FEATURES call Steven Price
2019-08-19 14:04 ` [PATCH v2 4/9] KVM: arm64: Support stolen time reporting via shared structure Steven Price
2019-08-19 16:40 ` Marc Zyngier
2019-08-21 10:27 ` Steven Price
2019-08-19 14:04 ` [PATCH v2 5/9] KVM: Allow kvm_device_ops to be const Steven Price
2019-08-19 14:04 ` [PATCH v2 6/9] KVM: arm64: Provide a PV_TIME device to user space Steven Price
2019-08-19 14:04 ` [PATCH v2 7/9] arm/arm64: Provide a wrapper for SMCCC 1.1 calls Steven Price
2019-08-19 14:04 ` [PATCH v2 8/9] arm/arm64: Make use of the SMCCC 1.1 wrapper Steven Price
2019-08-19 14:04 ` [PATCH v2 9/9] arm64: Retrieve stolen time as paravirtualized guest Steven Price
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