On Mon, May 17, 2021 at 03:27:13PM +0100, Alexandru Elisei wrote: > [ Upstream commit 263d6287da1433aba11c5b4046388f2cdf49675c ] > > When a VCPU is created, the kvm_vcpu struct is initialized to zero in > kvm_vm_ioctl_create_vcpu(). On VHE systems, the first time > vcpu.arch.mdcr_el2 is loaded on hardware is in vcpu_load(), before it is > set to a sensible value in kvm_arm_setup_debug() later in the run loop. The > result is that KVM executes for a short time with MDCR_EL2 set to zero. > > This has several unintended consequences: > > * Setting MDCR_EL2.HPMN to 0 is constrained unpredictable according to ARM > DDI 0487G.a, page D13-3820. The behavior specified by the architecture > in this case is for the PE to behave as if MDCR_EL2.HPMN is set to a > value less than or equal to PMCR_EL0.N, which means that an unknown > number of counters are now disabled by MDCR_EL2.HPME, which is zero. > > * The host configuration for the other debug features controlled by > MDCR_EL2 is temporarily lost. This has been harmless so far, as Linux > doesn't use the other fields, but that might change in the future. > > Let's avoid both issues by initializing the VCPU's mdcr_el2 field in > kvm_vcpu_vcpu_first_run_init(), thus making sure that the MDCR_EL2 register > has a consistent value after each vcpu_load(). > > [ v5.4 backport: added stub for KVM/arm that fixes compilation errors ] Thanks for both backports, now queued up. greg k-h
