When migrating ARM guests accross same machines with different host
kernels we are likely to encounter failures such as:
"failed to load cpu:cpreg_vmstate_array_len"
This is due to the fact KVM exposes a different number of registers
to qemu on source and destination. When trying to migrate a bigger
register set to a smaller one, qemu cannot save the CPU state.
For example, recently we faced such kind of situations with:
- unconditionnal exposure of KVM_REG_ARM_VENDOR_HYP_BMAP_2 FW pseudo
register from v6.16 onwards. Causes backward migration failure.
- removal of unconditionnal exposure of TCR2_EL1, PIRE0_EL1, PIR_EL1
from v6.13 onwards. Causes forward migration failure.
This situation is really problematic for distributions which want to
guarantee forward and backward migration of a given machine type
between different releases.
This small series tries to address that issue by introducing CPU
array properties that list the registers to ignore or to fake according
to the situation. An example is given to illustrate how those props
could be used to apply compats for machine types supposed to "see" the
same register set accross various host kernels.
The first patch improves the tracing so that we can quickly detect
which registers are unexpected and cause the migration failure. Missing
registers are also traced. Those do not fail migration but their default
value is kept on the destination.
Then we introduce the infrastructure to handle 'hidden' registers and
'fake' registers.
Eric Auger (7):
target/arm/machine: Improve traces on register mismatch during
migration
target/arm/kvm: Introduce the concept of hidden KVM regs
target/arm/kvm: Introduce the concept of enforced/fake registers
kvm-all: Add the capability to blacklist some KVM regs
target/arm/cpu: Implement hide_reg callback()
target/arm/kvm: Expose kvm-hidden-regs and kvm-fake-regs properties
hw/arm/virt: [DO NOT UPSTREAM] Enforce compatibility with older
kernels
include/hw/core/cpu.h | 2 ++
target/arm/cpu.h | 42 ++++++++++++++++++++++++
accel/kvm/kvm-all.c | 12 +++++++
hw/arm/virt.c | 19 +++++++++++
target/arm/cpu.c | 12 +++++++
target/arm/kvm.c | 73 ++++++++++++++++++++++++++++++++++++++++-
target/arm/machine.c | 71 +++++++++++++++++++++++++++++++++++----
target/arm/trace-events | 11 +++++++
8 files changed, 235 insertions(+), 7 deletions(-)
--
2.49.0
