Linux Plumbers Conference 2024

Session

KVM Microconference

19 Sept 2024, 10:00

Matrix chat

Description

CFP closes on July 12th.

KVM (Kernel-based Virtual Machine) enables the use of hardware features to
improve the efficiency, performance, and security of virtual machines (VMs)
created and managed by userspace. KVM was originally developed to accelerate
VMs running a traditional kernel and operating system, in a world where the
host kernel and userspace are part of the VM's trusted computing base (TCB).

KVM has long since expanded to cover a wide (and growing) array of use cases,
e.g. sandboxing untrusted workloads, deprivileging third party code, reducing
the TCB of security sensitive workloads, etc. The expectations placed on KVM
have also matured accordingly, e.g. functionality that once was "good enough"
no longer meets the needs and demands of KVM users.

The KVM Microconference will focus on how to evolve KVM and adjacent subsystems
in order to satisfy new and upcoming requirements. Of particular interest is
extending and enhancing guest_memfd, a guest-first memory API that was heavily
discussed at the 2023 KVM Microconference, and merged in v6.8.

The KVM MC is expected to have strong representation from maintainers (KVM and
non-KVM), hardware vendors (Intel, AMD, ARM, RISC-V, etc), cloud (AWS, Google,
Oracle, etc), client (Android, ChromeOS), and open source stalwarts such as
Red Hat and SUSE.

Potential Topics:
- Removing guest memory from the host kernel's direct map[1]
- Mapping guest_memfd into host userspace[2]
- Hugepage support for guest_memfd[3]
- Eliminating "struct page" for guest_memfd
- Passthrough/mediated PMU virtualization[4]
- Pagetable-based Virtual Machine (PVM)[5]
- Optimizing/hardening KVM usage of GUP[6][7]
- Live migration support for guest_memfd
- Defining KVM requirements for hardware vendors
- Utilizing "fault" injection to increase test coverage of edge cases

[1] https://lore.kernel.org/all/cc1bb8e9bc3e1ab637700a4d3defeec95b55060a.camel@amazon.com
[2] https://lore.kernel.org/all/20240222161047.402609-1-tabba@google.com
[3] https://lore.kernel.org/all/CABgObfa=DH7FySBviF63OS9sVog_wt-AqYgtUAGKqnY5Bizivw@mail.gmail.com
[4] https://lore.kernel.org/all/20240126085444.324918-1-xiong.y.zhang@linux.intel.com
[5] https://lore.kernel.org/all/20240226143630.33643-1-jiangshanlai@gmail.com
[6] https://lore.kernel.org/all/CABgObfZCay5-zaZd9mCYGMeS106L055CxsdOWWvRTUk2TPYycg@mail.gmail.com
[7] https://lore.kernel.org/all/20240320005024.3216282-1-seanjc@google.com

Presentation materials

Live stream

133. Pagetable-based Virtual Machine (PVM) as a PV flavor for KVM

Lai Jiangshan (AntGroup), Wenlong Hou

19/09/2024, 10:00

Nowadays, there are various needs to run a VM in the public cloud, such as running a security container to isolate workloads or encapsulating an application into a VM for migration or rapid kernel testing utilizing cost-effective spot VMs. However, nested virtualization on KVM requires hardware support and is usually disabled by the cloud provider for safety reasons. Additionally, the current...

48. Mediated passthrough vPMU for KVM

Mingwei Zhang (Google)

19/09/2024, 10:30

BACKGROUND

KVM has supported vPMU for years as the emulated vPMU. In particular, KVM presents a virtual PMU to guests where accesses to PMU get trapped and converted into perf events. These perf events get scheduled along with other perf events at the host level, sharing the HW resource. In the emulated vPMU design, KVM is a client of the perf subsystem and has no control of...

206. guest_memfd roadmap - introduction

Paolo Bonzini (Red Hat, Inc.)

19/09/2024, 11:00

This session should group discussions on future extensions to guest_memfd, including:

• in-place replacement and userspace mmap of shared pages (https://lore.kernel.org/kvm/20240618-exclusive-gup-v1-0-30472a19c5d1@quicinc.com/)
• large folios
• hugetlbfs
• live migration aka send/receive (pages that are encrypted but accessible from userspace)

239. Guest private memory for software-based hypervisors

Fuad Tabba (Google)

19/09/2024, 11:10

This talk presents different proposals for supporting guest private memory in Android for Arm64 in the pKVM and the Gunyah hypervisors.

Confidential computing is gaining popularity, with hardware-based (Intel TDX, AMD SEV, Arm CCA) and software-based (pKVM, Gunyah) solutions. A common aspect is the ability to create a "protected" guest, whose data is neither inaccessible by other VMs nor by...

44. 1G page support for guest_memfd

Vishal Annapurve

19/09/2024, 12:00

[guest_memfd][1] is a new feature providing a guest-first memory subsystem internal to KVM. Being internal to KVM opens guest_memfd up to virtualization-specific features, enhancements and optimizations.

A notable feature that guest_memfd currently lacks is 1G page support.

Here are some key benefits of 1G page support:
Better performance due to
Increased hit rate in the TLB
Faster...

205. Removing guest memory from the host kernel's direct map

Patrick Roy (Amazon UK)

19/09/2024, 12:30

Since the discovery of Spectre and Meltdown in 2018, transient execution attacks are being discovered regularly, both in old and new hardware. Mitigation involves applying specific patches for each vulnerability, and is often costly in terms of performance, leading to cloud computing providers to seek more general mitigations.

The majority of these attacks are based on the presence of a...

287. Post-copy live migration with guest_memfd

James Houghton (Google)

19/09/2024, 13:00

Problem: traditional implementation of post-copy live migration

The key challenge with post-copy live migration is intercepting accesses to particular pages of guest memory. Today, the only way to do this is to use userfaultfd, an mm feature that intercepts page faults (and other events). KVM, after translating a GFN to an HVA, will call GUP to translate the HVA to an HPA, thereby...