Add a core_scheduling option to --cpus with three modes of operation.
This feature takes advantage of a kernel feature that restricts
scheduling of processes on the SMT threads on the same core. This is
useful for mitigating certain classes of side-channel attacks and has
better performance that disabling SMT on the CPU.
- vm (default): All vCPU threads share one core scheduling cookie.
They may be co-scheduled on SMT siblings while host threads are
excluded - this has minimal performance impact and can even
potentially improve performance from co-location.
- vcpu: Each vCPU gets a unique cookie preventing any two vCPUs from
sharing SMT siblings. This has the strongest isolation but at some
compromise of performance.
- off: No core scheduling applied (old behaviour).
This isolation is done by the kernel maintaining a "cookie" - threads
with the same cookie can share the same core.
In vCPU mode each vCPU thread the cookie is created when the thread
starts and each gets a unique cookie. For VM mode the first vCPU thread
(the leader) will create the cookie. All other vCPU threads started (via
hotplug or during boot) will have that cookie shared to it.
EINVAL/ENODEV from prctl is silently ignored so this works transparently
on kernels older than 5.14 that lack PR_SCHED_CORE or when SMT disabled.
Full details of this kernel feature can be found at:
https://docs.kernel.org/admin-guide/hw-vuln/core-scheduling.html
This implementation was inspired by crosvm's implementation - in
particular the enable_core_scheduling() function.
This is challenging to test via integration testing but the logging of
the received cookie shows it working:
VM case:
cloud-hypervisor: 0.243102s: <vcpu1> INFO:vmm/src/cpu.rs:1247 -- vCPU 1: core scheduling cookie = 0x33e4c167
cloud-hypervisor: 0.243102s: <vcpu0> INFO:vmm/src/cpu.rs:1247 -- vCPU 0: core scheduling cookie = 0x33e4c167
vCPU case:
cloud-hypervisor: 0.089356s: <vcpu0> INFO:vmm/src/cpu.rs:1247 -- vCPU 0: core scheduling cookie = 0x13993ad6
cloud-hypervisor: 0.089380s: <vcpu1> INFO:vmm/src/cpu.rs:1247 -- vCPU 1: core scheduling cookie = 0xd48e86e
Signed-off-by: Rob Bradford <rbradford@meta.com>
Some description in the device document were inconsistent with the
source code. Also fix some syntax issues to make the sentences more
fluent.
Signed-off-by: Yi Wang <foxywang@tencent.com>
This patch updates the documentation to reflect the newly added
nested CPU feature option in the CLI.
Signed-off-by: Muminul Islam <muislam@microsoft.com>
AMX is an x86 extension adding hardware units for matrix
operations (int and float dot products). The goal of the extension is
to provide performance enhancements for these common operations.
On Linux, AMX requires requesting the permission from the kernel prior
to use. Guests wanting to make use of the feature need to have the
request made prior to starting the vm.
This change then adds the first --cpus features option amx that when
passed will enable AMX usage for guests (needs a 5.17+ kernel) or
exits with failure.
The activation is done in the CpuManager of the VMM thread as it
allows migration and snapshot/restore to work fairly painlessly for
AMX enabled workloads.
Signed-off-by: William Douglas <william.douglas@intel.com>
This new document describes the available options for the parameter
`--cpus`, how to use them and what is their usage.
Fixes#3317
Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
