diff options
| author | Michael Roth <michael.roth@amd.com> | 2024-07-09 23:10:05 -0500 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2024-07-16 10:45:06 +0200 |
| commit | 9d38d9dca2a81aaf5752d45d221021ef96d496cd (patch) | |
| tree | 5c5556011908b5c08be2d81ca8ce00384aea5a96 /qapi/qom.json | |
| parent | 959269e910944c03bc13f300d65bf08b060d5d0f (diff) | |
i386/sev: Don't allow automatic fallback to legacy KVM_SEV*_INIT
Currently if the 'legacy-vm-type' property of the sev-guest object is
'on', QEMU will attempt to use the newer KVM_SEV_INIT2 kernel
interface in conjunction with the newer KVM_X86_SEV_VM and
KVM_X86_SEV_ES_VM KVM VM types.
This can lead to measurement changes if, for instance, an SEV guest was
created on a host that originally had an older kernel that didn't
support KVM_SEV_INIT2, but is booted on the same host later on after the
host kernel was upgraded.
Instead, if legacy-vm-type is 'off', QEMU should fail if the
KVM_SEV_INIT2 interface is not provided by the current host kernel.
Modify the fallback handling accordingly.
In the future, VMSA features and other flags might be added to QEMU
which will require legacy-vm-type to be 'off' because they will rely
on the newer KVM_SEV_INIT2 interface. It may be difficult to convey to
users what values of legacy-vm-type are compatible with which
features/options, so as part of this rework, switch legacy-vm-type to a
tri-state OnOffAuto option. 'auto' in this case will automatically
switch to using the newer KVM_SEV_INIT2, but only if it is required to
make use of new VMSA features or other options only available via
KVM_SEV_INIT2.
Defining 'auto' in this way would avoid inadvertantly breaking
compatibility with older kernels since it would only be used in cases
where users opt into newer features that are only available via
KVM_SEV_INIT2 and newer kernels, and provide better default behavior
than the legacy-vm-type=off behavior that was previously in place, so
make it the default for 9.1+ machine types.
Cc: Daniel P. Berrangé <berrange@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
cc: kvm@vger.kernel.org
Signed-off-by: Michael Roth <michael.roth@amd.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Link: https://lore.kernel.org/r/20240710041005.83720-1-michael.roth@amd.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'qapi/qom.json')
| -rw-r--r-- | qapi/qom.json | 18 |
1 files changed, 11 insertions, 7 deletions
diff --git a/qapi/qom.json b/qapi/qom.json index 8e75a419c3..7eccd2e14e 100644 --- a/qapi/qom.json +++ b/qapi/qom.json @@ -924,12 +924,16 @@ # @handle: SEV firmware handle (default: 0) # # @legacy-vm-type: Use legacy KVM_SEV_INIT KVM interface for creating the VM. -# The newer KVM_SEV_INIT2 interface syncs additional vCPU -# state when initializing the VMSA structures, which will -# result in a different guest measurement. Set this to -# maintain compatibility with older QEMU or kernel versions -# that rely on legacy KVM_SEV_INIT behavior. -# (default: false) (since 9.1) +# The newer KVM_SEV_INIT2 interface, from Linux >= 6.10, syncs +# additional vCPU state when initializing the VMSA structures, +# which will result in a different guest measurement. Set +# this to 'on' to force compatibility with older QEMU or kernel +# versions that rely on legacy KVM_SEV_INIT behavior. 'auto' +# will behave identically to 'on', but will automatically +# switch to using KVM_SEV_INIT2 if the user specifies any +# additional options that require it. If set to 'off', QEMU +# will require KVM_SEV_INIT2 unconditionally. +# (default: off) (since 9.1) # # Since: 2.12 ## @@ -939,7 +943,7 @@ '*session-file': 'str', '*policy': 'uint32', '*handle': 'uint32', - '*legacy-vm-type': 'bool' } } + '*legacy-vm-type': 'OnOffAuto' } } ## # @SevSnpGuestProperties: |