[v6] Introduce support for confidential guest reset (x86)

[PATCH v6 00/35] Introduce support for confidential guest reset (x86)

Posted by Ani Sinha 1 month, 2 weeks ago

This change introduces support for confidential guests
(SEV-ES, SEV-SNP and TDX) to reset/reboot just like other non-confidential
guests. Currently, a reboot intiated from the confidential guest results
in termination of the QEMU hypervisor as the CPUs are not resettable. As the
initial state of the guest including private memory is locked and encrypted,
the contents of that memory will not be accessible post reset. Hence a new
KVM file descriptor must be opened to create a new confidential VM context
closing the old one. All KVM VM specific ioctls must be called again. New
VCPU file descriptors must be created against the new KVM fd and most VCPU
ioctls must be called again as well.

This change perfoms closing of the old KVM fd and creating a new one. After
the new KVM fd is opened, all generic and architecture specific ioctl calls
are issued again. Notifiers are added to notify subsystems that:
- The KVM file fd is about to be changed to state sync-ing from KVM to QEMU
should be done if required.
- The KVM file fd has changed, so ioctl calls to the new KVM fd has to be
performed again.
- That new VCPU fds are created so that VCPU ioctl calls must be called again
where required.

Specific subsystems use these notifiers to re-issue ioctl calls where required.

Changes are made to SEV and TDX modules to reinitialize the confidential guest
state and seal it again. Along the way, some bug fixes are made so that some
initialization functions can be called again. Some refactoring of existing
code is done so that both init and reset paths can use them.

Tested by triggering reset through guest console as well as QMP "system_reset" command.
All tests use multi vcpu (SMP) guests.

Tested on TDX hardware running with RHEL-9.6 on the host.
Used Fedora 43 guest (cloud image) + basic UKI kernel boot (fc43 kernel).

Tested on SEV-SNP on two diferent hosts - one running RHEL 9.8, other Fedora 43.
Used Fedora 43 guest (cloud image) + basic UKI kernel boot (fc43 kernel).

Tested SEV-ES on a SEV-SNP host running Fedora 42 on the host.
Basic UKI kernel boot only (fc39 and fc43 kernels).
It is to be noted that Fedora 43 and RHEL hosts seems to no longer support SEV-ES and
bails out with the following error:

qemu-system-x86_64: -accel kvm: sev_launch_start: LAUNCH_START ret=1 fw_error=21 'Feature not supported'
qemu-system-x86_64: -accel kvm: sev_common_kvm_init: failed to create encryption context
qemu-system-x86_64: -accel kvm: failed to initialize kvm: Operation not permitted

For non-coco ran the added functional tests on a fc43 host:

$ ./build/run tests/functional/x86_64/test_vmfd_change_reboot.py
TAP version 13
ok 1 test_vmfd_change_reboot.KVMGuest.test_reset_console
ok 2 test_vmfd_change_reboot.KVMGuest.test_reset_hyperv_vmbus
ok 3 test_vmfd_change_reboot.KVMGuest.test_reset_kvmpit
ok 4 test_vmfd_change_reboot.KVMGuest.test_reset_qmp
ok 5 test_vmfd_change_reboot.KVMGuest.test_reset_xen_emulation
1..5

For regression, ran QEMU CI pipeline and it passes:
https://gitlab.com/anisinha/qemu/-/pipelines/2346276955

CC: qemu-devel@nongnu.org
CC: pbonzini@redhat.com
CC: kraxel@redhat.com
CC: vkuznets@redhat.com
CC: graf@amazon.com

Changelog:

v6:
- fixed regression issue reported by Cleber on v4/v5.
- reworked patch #28 as per review comments from v5.
- tags added.
- rebased.

v5:
- suggestions from v4 added.
- xen code refactoring seperated into a new patch.
- minor fixes.
- tags added.
- rebased.

v4:
- Fixed reset on non-coco with qmp "system_reset" command.
- Numerious misc fixes.
- addressed review comments from v3.
- dropped three patches that are not required.
- Added more functional tests including one vmbus test.
- added noop callbacks to stubs/kvm removing them from arch specific headers.
- Tags added.
- Rebased.

v3:
- Combined pre and post vmfd change notifier into one.
- rename kvm_arch_vmfd_change_ops() -> kvm_arch_on_vmfd_change()
- reuse kvm_arch_init() code in kvm_arch_on_vmfd_change()
- moved around migration blockers and notifers to more appropriate place.
- fixed Xen emulation.
- fixed SEV-ES reset.
- fixed/reorganized reset code in system/runstate.c
- can_rebuild_guest_state is now a boolean not a callback.
- misc fixes.
- added a functional test for Xen emulation with vmfd change.
- rebased.

v2:
- Bugfixes.
- Added a new machine option so that we can exercize most of the non-coco changes
related to reboot on non-coco platforms.
- added a new functional test. Currently its skipped on CI pipeline as KVM is not
enabled (no /dev/kvm on the container)for QEMU CI tests. It can be run manually and it
passes on those systems where KVM is enabled.
- Addressed comments from v1 with regards to refactoring of code, code simplication by
removal of redundant stuff, moved around code
so that notifiers, migration blockers are added only on one place.
- Added some tracepoints for future debugging on newly added functions.
- Rebased.

Ani Sinha (35):
i386/kvm: avoid installing duplicate msr entries in msr_handlers
accel/kvm: add confidential class member to indicate guest rebuild
capability
hw/accel: add a per-accelerator callback to change VM accelerator
handle
system/physmem: add helper to reattach existing memory after KVM VM fd
change
accel/kvm: add changes required to support KVM VM file descriptor
change
accel/kvm: mark guest state as unprotected after vm file descriptor
change
accel/kvm: add a notifier to indicate KVM VM file descriptor has
changed
accel/kvm: notify when KVM VM file fd is about to be changed
i386/kvm: unregister smram listeners prior to vm file descriptor
change
kvm/i386: implement architecture support for kvm file descriptor
change
i386/kvm: refactor xen init into a new function
hw/i386: refactor x86_bios_rom_init for reuse in confidential guest
reset
hw/i386: export a new function x86_bios_rom_reload
kvm/i386: reload firmware for confidential guest reset
accel/kvm: rebind current VCPUs to the new KVM VM file descriptor upon
reset
i386/tdx: refactor TDX firmware memory initialization code into a new
function
i386/tdx: finalize TDX guest state upon reset
i386/tdx: add a pre-vmfd change notifier to reset tdx state
i386/sev: add migration blockers only once
i386/sev: add notifiers only once
i386/sev: free existing launch update data and kernel hashes data on
init
i386/sev: add support for confidential guest reset
hw/vfio: generate new file fd for pseudo device and rebind existing
descriptors
kvm/i8254: refactor pit initialization into a helper
kvm/i8254: add support for confidential guest reset
kvm/hyperv: add synic feature to CPU only if its not enabled
hw/hyperv/vmbus: add support for confidential guest reset
kvm/xen-emu: re-initialize capabilities during confidential guest
reset
ppc/openpic: create a new openpic device and reattach mem region on
coco reset
kvm/vcpu: add notifiers to inform vcpu file descriptor change
kvm/clock: add support for confidential guest reset
hw/machine: introduce machine specific option 'x-change-vmfd-on-reset'
tests/functional/x86_64: add functional test to exercise vm fd change
on reset
qom: add 'confidential-guest-reset' property for x86 confidential vms
migration: return EEXIST when trying to add the same migration blocker

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2.42.0