Xen project Mailing List

On Mon, Nov 12, 2018 at 12:31 PM Mirela Simonovic <mirela.simonovic@xxxxxxxxxx> wrote:

This series contains support for suspend to RAM (in the following text just
'suspend') for Xen on arm64. The implementation is aligned with the design
specification that has been proposed on xen-devel list:
https://lists.xenproject.org/archives/html/xen-devel/2017-12/msg01574.html

At a high-level the series contains:
1) Support for suspending guests via virtual PSCI SYSTEM_SUSPEND call
2) Support for resuming a guest on an interrupt targeted to that guest
3) Support for suspending Xen after dom0 finalizes the suspend
4) Support for resuming Xen on an interrupt that is targeted to a guest

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In more details:

*** About suspending/resuming guests

The patches included in this series allow PSCI compliant guests that have
support for suspend to RAM (e.g. echo mem > /sys/power/state in Linux) to
suspend and resume on top of Xen without any EL1 code changes.

During their suspend procedure guests will hot-unplug their secondary CPUs,
triggering Xen's virtual CPU_OFF PSCI implementation, and then finalize the
suspend from their boot CPU, triggering Xen's virtual SYSTEM_SUSPEND PSCI.
Guests will save/restore their own EL1 context on suspend/resume.

A guest is expected to leave enabled interrupts that are considered to be its
wake-up sources. Those interrupts will be able to wake up the guest. This holds
regardless of the state of the underlying software layers, i.e. whether Xen gets
suspended or not doesn't affect the ability of the guest to wake up.

First argument of SYSTEM_SUSPEND PSCI call is a resume entry point, from which
the guest assumes to start on resume. On resume, guests assume to be running in
an environment whose state matches the CPU state after reset, e.g. with reset
register values, MMU disabled, etc. To ensure this, Xen has to 'reset' the
VCPU context and save the resume entry point into program counter before the
guest's VCPU gets scheduled in on resume. This is done when the guest finalizes
its suspend by calling PSCI SYSTEM_SUSPEND. In addition, we need to ensure that
the resume-ready VCPU's context does not get overwritten later upon the context
switch when the VCPU is scheduled out.
Xen also needs to take care that the guest's view of GIC and timer gets saved.
Also, while a guest is suspended its watchdogs are paused, in order to avoid
watchdog triggered shutdown of a guest that has been asleep for a period of time
that is longer than the watchdog period.

After this point, from Xen's point of view a suspended guest has one VCPU
blocked, waiting for an interrupt. When such an interrupt comes, Xen will
unblock the VCPU of the suspended domain, which results in the guest resuming.

*** About suspending/resuming Xen

Xen starts its own suspend procedure once dom0 is suspended. Dom0 is
considered to be the decision maker for EL1 and EL2.
On suspend, Xen will first freeze all domains. Then, Xen disables physical
secondary CPUs, which leads to physical CPU_OFF to be called by each secondary
CPU. After that Xen finalizes the suspend from the boot CPU.

This consists of suspending the timer, i.e. suppressing its interrupts (we don't
want to be woken up by a timer, there is no VCPU ready to be scheduled). Then
the state of GIC is saved, console is suspended, and CPU context is saved. The
saved context tells where Xen needs to continue execution on resume.
Since Xen will resume with MMU disabled, the first thing to do in resume is to
resume memory management in order to be able to access the context that needs to
be restored (we know virtual address of the context data). Finally Xen calls
SYSTEM_SUSPEND PSCI to the EL3.

When resuming, all the steps done in suspend need to be reverted. This is
completed by unblocking dom0's VCPU, because we always want the dom0 to resume,
regardless of the target domain whose interrupt woke up Xen.

*** Handling of unprivileged guests during Xen suspend/resume

Any domU that is not suspended when dom0 suspends will be frozen, domUs that are
already suspended remain suspended. On resume the suspended domUs still remain
suspended (unless their wake interrupt caused Xen to wake) while the others will
be thawed.

For more details please refer to patches or the design specification:
https://lists.xenproject.org/archives/html/xen-devel/2017-12/msg01574.html

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The series does not include:
a) UART driver-specific suspend/resume that gets called when console suspends
b) SMMU suspend/resume
c) Suspend coordination support that would allow dom0 to request domUs to
suspend
These will be submitted in the following series.

Mirela Simonovic (16):
xen/arm: Implement PSCI system suspend call (virtual interface)
xen/arm: Save GIC and virtual timer context when the domain suspends
xen/arm: While a domain is suspended put its watchdogs on pause
xen/arm: Trigger Xen suspend when Dom0 completes suspend
xen/x86: Move freeze/thaw_domains into common files
xen/arm: Freeze domains on suspend and thaw them on resume
xen/arm: Disable/enable non-boot physical CPUs on suspend/resume
xen/arm: Add rcu_barrier() before enabling non-boot CPUs on resume
xen/arm: Implement GIC suspend/resume functions (gicv2 only)
xen/arm: Suspend/resume GIC on system suspend/resume
xen/arm: Suspend/resume timer interrupt generation
xen/arm: Implement PSCI SYSTEM_SUSPEND call (physical interface)
xen/arm: Resume memory management on Xen resume
xen/arm: Save/restore context on suspend/resume
xen/arm: Resume Dom0 after Xen resumes
xen/arm: Suspend/resume console on Xen suspend/resume

Saeed Nowshadi (2):
xen/arm: Move code that initializes VCPU context into a separate
function
xen/arm: Convert setting MMU page tables code into a routine

xen/arch/arm/Makefile | 1 +
xen/arch/arm/arm64/entry.S | 178 ++++++++++++++++++++++++
xen/arch/arm/arm64/head.S | 265 ++++++++++++++++++-----------------
xen/arch/arm/domain.c | 62 ++++++---
xen/arch/arm/gic-v2.c | 147 ++++++++++++++++++++
xen/arch/arm/gic.c | 27 ++++
xen/arch/arm/mm.c | 1 +
xen/arch/arm/psci.c | 16 +++
xen/arch/arm/suspend.c | 292 +++++++++++++++++++++++++++++++++++++++
xen/arch/arm/time.c | 22 +++
xen/arch/arm/vpsci.c | 19 +++
xen/arch/x86/acpi/power.c | 28 ----
xen/common/domain.c | 29 ++++
xen/common/schedule.c | 38 +++++
xen/include/asm-arm/gic.h | 8 ++
xen/include/asm-arm/perfc_defn.h | 1 +
xen/include/asm-arm/psci.h | 3 +
xen/include/asm-arm/suspend.h | 39 ++++++
xen/include/asm-arm/time.h | 3 +
xen/include/xen/domain.h | 1 +
xen/include/xen/sched.h | 11 ++
xen/include/xen/timer.h | 3 +
22 files changed, 1019 insertions(+), 175 deletions(-)
create mode 100644 xen/arch/arm/suspend.c
create mode 100644 xen/include/asm-arm/suspend.h

--
2.13.0

Re: [Xen-devel] [PATCH 00/18] xen/arm64: Suspend to RAM support for Xen