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commit fb544d1ca65a89f7a3895f7531221ceeed74ada7 upstream. We recently addressed a VMID generation race by introducing a read/write lock around accesses and updates to the vmid generation values. However, kvm_arch_vcpu_ioctl_run() also calls need_new_vmid_gen() but does so without taking the read lock. As far as I can tell, this can lead to the same kind of race: VM 0, VCPU 0 VM 0, VCPU 1 ------------ ------------ update_vttbr (vmid 254) update_vttbr (vmid 1) // roll over read_lock(kvm_vmid_lock); force_vm_exit() local_irq_disable need_new_vmid_gen == false //because vmid gen matches enter_guest (vmid 254) kvm_arch.vttbr = <PGD>:<VMID 1> read_unlock(kvm_vmid_lock); enter_guest (vmid 1) Which results in running two VCPUs in the same VM with different VMIDs and (even worse) other VCPUs from other VMs could now allocate clashing VMID 254 from the new generation as long as VCPU 0 is not exiting. Attempt to solve this by making sure vttbr is updated before another CPU can observe the updated VMID generation. Cc: stable@vger.kernel.org Fixes: f0cf47d939d0 "KVM: arm/arm64: Close VMID generation race" Reviewed-by: Julien Thierry <julien.thierry@arm.com> Signed-off-by: Christoffer Dall <christoffer.dall@arm.com> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.