From: Steven Price <steven.price@arm.com>
To: kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org
Cc: Marc Zyngier <marc.zyngier@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Steven Price <steven.price@arm.com>
Subject: [RFC PATCH v2 01/12] KVM: arm64: Document PV-time interface
Date: Wed, 12 Dec 2018 15:02:15 +0000 [thread overview]
Message-ID: <20181212150226.38051-2-steven.price@arm.com> (raw)
In-Reply-To: <20181212150226.38051-1-steven.price@arm.com>
We introduce a paravirtualization interface for KVM/arm64 based on the
"Arm Paravirtualized Time for Arm-Base Systems" specification DEN 0057A.
User space can specify a reserved area of memory for the guest and
inform KVM to populate the memory with information on stolen time and
Live Physical Time (LPT) that can be used to derive a stable
counter/timer for a guest subject to migration between hosts with
different counter frequencies.
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/virtual/kvm/arm/pvtime.txt | 169 +++++++++++++++++++++++
1 file changed, 169 insertions(+)
create mode 100644 Documentation/virtual/kvm/arm/pvtime.txt
diff --git a/Documentation/virtual/kvm/arm/pvtime.txt b/Documentation/virtual/kvm/arm/pvtime.txt
new file mode 100644
index 000000000000..1870b904075b
--- /dev/null
+++ b/Documentation/virtual/kvm/arm/pvtime.txt
@@ -0,0 +1,169 @@
+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 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 and a concept of Live Physical Time (LPT) which
+represents time during which the guest is running and works across migrations.
+
+Three new SMCCC compatible hypercalls are defined:
+
+PV_FEATURES 0xC5000020
+PV_TIME_LPT 0xC5000021
+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.
+
+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_LPT
+ Function ID: (uint32) : 0xC5000021
+ Flags: (uint32) : Bit[0]: Request migration interrupts
+ (not currently supported by KVM)
+ Return value: (int64) : IPA of the shared live physical time data
+ structure or negative error code on failure:
+ NOT_SUPPORTED (-1)
+ INVALID_PARAMETERS (-2)
+
+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)
+
+Live Physical Time
+------------------
+
+The structure pointed to by the PV_TIME_LPT hypercall is as follows:
+
+ Field | Byte Length | Byte Offset | Description
+ --------------- | ----------- | ----------- | -------------------------------
+ Revision | 4 | 0 | Must be 0 for this revision
+ Attributes | 4 | 4 | Must be 0
+ sequence_number | 8 | 8 | Bit 0: reserved
+ | | | Bits 1:63 number of migrations
+ scale_mult | 8 | 16 | Multiplier to scale from native
+ | | | frequency to PV frequency
+ shift | 4 | 24 | Shift applied before multiplier
+ Reserved | 4 | 28 | Must be 0
+ Fn | 8 | 32 | Native frequency
+ Fpv | 8 | 40 | Paravirtualized frequency seen
+ | | | by guest
+ div_by_fpv_mult | 8 | 48 | Multiplier to implement fast
+ | | | divide by Fpv
+
+Where scale_mult is defined as 2^(64-shift) * Fpv / Fn
+
+The structure will be updated by the hypervisor whenever the guest is migrated
+to a new host. 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.
+
+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 periodically as time is stolen
+from the 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 by 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);
+
+The guest IPA of the structures must be given to KVM. This is the address of
+the LPT structure and the base address of an array of stolen time structures
+(one for each VCPU). For example:
+
+ struct kvm_device_attr lpt_base = {
+ .group = KVM_DEV_ARM_PV_TIME_PADDR,
+ .attr = KVM_DEV_ARM_PV_TIME_LPT,
+ .addr = (u64)(unsigned long)&lpt_paddr
+ };
+ struct kvm_device_attr st_base = {
+ .group = KVM_DEV_ARM_PV_TIME_PADDR,
+ .attr = KVM_DEV_ARM_PV_TIME_ST,
+ .addr = (u64)(unsigned long)&st_paddr
+ };
+
+ ioctl(pvtime_fd, KVM_SET_DEVICE_ATTR, &lpt_base);
+ ioctl(pvtime_fd, KVM_SET_DEVICE_ATTR, &st_base);
+
+The paravirtualized frequency of the guest can also be set. By default this
+will be the counter frequency of the host. However when migrating a guest from
+another host, this must be manually set to ensure that the guest sees the same
+frequency.
+
+ u32 frequency;
+
+ struct kvm_device_attr lpt_freq = {
+ .group = KVM_DEV_ARM_PV_TIME_FREQUENCY,
+ .attr = KVM_DEV_ARM_PV_TIME_LPT,
+ .addr = (u64)(unsigned long)&frequency
+ };
+
+ ioctl(pvtime_fd, KVM_SET_DEVICE_ATTR, &lpt_freq);
+
+For migration (or save/restore) of a guest it is necessary to save the contents
+of the shared pages and later restore them. KVM_DEV_ARM_PV_TIME_STATE_SIZE
+provides the size of this data and KVM_DEV_ARM_PV_TIME_STATE allows the state
+to be read/written. The state for stolen time and LPT are accessed separately.
+It is also necessary for the physical address and frequency to be set
+identically when restoring. The kernel will update the structure on first run
+of the vCPU(s) to contain the new coefficients.
+
+ void *save_state(int fd, u64 attr, u32 *size) {
+ struct kvm_device_attr get_size = {
+ .group = KVM_DEV_ARM_PV_TIME_STATE_SIZE,
+ .attr = attr,
+ .addr = (u64)(unsigned long)size
+ };
+
+ ioctl(fd, KVM_GET_DEVICE_ATTR, get_size);
+
+ void *buffer = malloc(*size);
+
+ struct kvm_device_attr get_state = {
+ .group = KVM_DEV_ARM_PV_TIME_STATE,
+ .attr = attr,
+ .addr = (u64)(unsigned long)size
+ };
+
+ ioctl(fd, KVM_GET_DEVICE_ATTR, buffer);
+ }
+
+ void *lpt_state = save_state(pvtime_fd, KVM_DEV_ARM_PV_TIME_LPT, &lpt_size);
+ void *st_state = save_state(pvtime_fd, KVM_DEV_ARM_PV_TIME_ST, &st_size);
+
--
2.19.2
next prev parent reply other threads:[~2018-12-12 15:03 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-12 15:02 [RFC PATCH v2 00/12] arm64: Paravirtualized time support Steven Price
2018-12-12 15:02 ` Steven Price [this message]
2018-12-12 15:02 ` [RFC PATCH v2 02/12] KVM: arm/arm64: Factor out hypercall handling from PSCI code Steven Price
2018-12-12 15:02 ` [RFC PATCH v2 03/12] arm/arm64: Provide a wrapper for SMCCC 1.1 calls Steven Price
2018-12-12 15:02 ` [RFC PATCH v2 04/12] arm/arm64: Make use of the SMCCC 1.1 wrapper Steven Price
2018-12-12 15:02 ` [RFC PATCH v2 05/12] KVM: arm64: Implement PV_FEATURES call Steven Price
2018-12-12 15:02 ` [RFC PATCH v2 06/12] KVM: arm64: Support stolen time reporting via shared structure Steven Price
2018-12-12 15:02 ` [RFC PATCH v2 07/12] arm64: Retrieve stolen time as paravirtualized guest Steven Price
2018-12-12 15:02 ` [RFC PATCH v2 08/12] KVM: Allow kvm_device_ops to be const Steven Price
2018-12-12 15:02 ` [RFC PATCH v2 09/12] KVM: arm64: Provide a PV_TIME device to user space Steven Price
2018-12-12 15:02 ` [RFC PATCH v2 10/12] KVM: arm64: Support Live Physical Time reporting Steven Price
2018-12-12 15:02 ` [RFC PATCH v2 11/12] clocksource: arm_arch_timer: Use paravirtualized LPT Steven Price
2018-12-12 15:02 ` [RFC PATCH v2 12/12] KVM: arm64: Export LPT using PV_TIME device Steven Price
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20181212150226.38051-2-steven.price@arm.com \
--to=steven.price@arm.com \
--cc=catalin.marinas@arm.com \
--cc=kvmarm@lists.cs.columbia.edu \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=marc.zyngier@arm.com \
--cc=will.deacon@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).