QEMU needs to perform memslots operations like merging and splitting, and each operation requires more than a single ioctl. Therefore if a vcpu is concurrently reading the same memslots, it could end up reading something that was temporarly deleted. For example, merging two memslots into one would imply: DELETE(m1) DELETE(m2) CREATE(m1+m2) And a vcpu could attempt to read m2 right after it is deleted, but before the new one is created. This approach is 100% QEMU-based. No KVM API modification is involved, but implies that QEMU must make sure no new ioctl is running and all vcpus are stopped. The logic and code are basically taken from David Hildenbrand proposal given a while ago while reviewing a previous attempt where I suggested to solve the above problem directly in KVM by extending its API. This is the original code: https://github.com/davidhildenbrand/qemu/commit/86b1bf546a8d00908e33f7362b0b61e2be8dbb7a I just split the patch in three smaller patches, and used a QemuLockCnt instead of counter + mutex. RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1979276 Emanuele David Hildenbrand (1): kvm: Atomic memslot updates Emanuele Giuseppe Esposito (2): KVM: keep track of running ioctls KVM: keep track of running vcpu ioctls accel/kvm/kvm-all.c | 175 ++++++++++++++++++++++++++++++++++++--- hw/core/cpu-common.c | 2 + include/hw/core/cpu.h | 3 + include/sysemu/kvm_int.h | 8 ++ 4 files changed, 177 insertions(+), 11 deletions(-) -- 2.31.1
