CVE-2026-98465: RISC-V: KVM: Serialize IMSIC attributes with vCPU migration

In the Linux kernel, the following vulnerability has been resolved:

RISC-V: KVM: Serialize IMSIC attributes with vCPU migration

KVM device ioctls are not serialized against KVMRUN. As a result, kvmriscvaiaimsicrwattr() can snapshot the physical CPU and HGEI of an IMSIC VS-file before a concurrent vCPU migration releases it.

The HGEI can then be allocated to another vCPU before imsicvsfilerw() uses the stale tuple. A GET or SET attribute may consequently access the new owner's interrupt file.

Serialize the entire IMSIC attribute operation with the target vCPU mutex. This prevents the VS-file from being migrated and recycled until the attribute access completes. Acquire the mutex killably so that the device ioctl remains interruptible while waiting for KVMRUN to finish.