在 2022/1/5 上午3:49, Raghavendra Rao Ananta 写道:
KVM regularly introduces new hypercall services to the guests without any consent from the Virtual Machine Manager (VMM). This means, the guests can observe hypercall services in and out as they migrate across various host kernel versions. This could be a major problem if the guest discovered a hypercall, started using it, and after getting migrated to an older kernel realizes that it's no longer available. Depending on how the guest handles the change, there's a potential chance that the guest would just panic. As a result, there's a need for the VMM to elect the services that it wishes the guest to discover. VMM can elect these services based on the kernels spread across its (migration) fleet. To remedy this, extend the existing firmware psuedo-registers, such as KVM_REG_ARM_PSCI_VERSION, for all the hypercall services available.
Haven't gone through the series but I wonder whether it's better to have a (e)BPF filter for this like seccomp.
Thanks
These firmware registers are categorized based on the service call owners, and unlike the existing firmware psuedo-registers, they hold the features supported in the form of a bitmap. The capability, KVM_CAP_ARM_HVC_FW_REG_BMAP, is used to announce this extension, which returns the number of psuedo-firmware registers supported. During the VM initialization, the registers holds an upper-limit of the features supported by the corresponding registers. It's expected that the VMMs discover the features provided by each register via GET_ONE_REG, and writeback the desired values using SET_ONE_REG. KVM allows this modification only until the VM has started. Older VMMs can simply ignore the capability and the hypercall services will be exposed unconditionally to the guests, thus ensuring backward compatibility. In this patch, the framework adds the register only for ARM's standard secure services (owner value 4). Currently, this includes support only for ARM True Random Number Generator (TRNG) service, with bit-0 of the register representing mandatory features of v1.0. Other services are momentarily added in the upcoming patches. Signed-off-by: Raghavendra Rao Ananta<rananta@xxxxxxxxxx>
