Due to the introduction of the raw_spinlock for the KVM openpic, guests with a high number of VCPUs may induce great latencies on the underlying RT Linux system (e.g. cyclictest reports latencies of ~15ms for guests with 24 VCPUs). This can be further aggravated by sending a lot of external interrupts to the guest. A malicious app can abuse this scenario, causing a DoS of the host Linux. Until the KVM openpic code is refactored to use finer lock granularity, impose a limitation on the number of VCPUs a guest can have when running on a PREEMPT_RT_FULL system with KVM_MPIC emulation. Signed-off-by: Mihai Caraman <mihai.caraman@xxxxxxxxxxxxx> Signed-off-by: Bogdan Purcareata <bogdan.purcareata@xxxxxxxxxxxxx> Reviewed-by: Scott Wood <scottwood@xxxxxxxxxxxxx> --- arch/powerpc/include/asm/kvm_host.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h index 8ef0512..6f6b928 100644 --- a/arch/powerpc/include/asm/kvm_host.h +++ b/arch/powerpc/include/asm/kvm_host.h @@ -36,8 +36,14 @@ #include <asm/cacheflush.h> #include <asm/hvcall.h> +#if defined(CONFIG_PREEMPT_RT_FULL) && defined(CONFIG_KVM_MPIC) +/* Limit the number of vcpus due to in-kernel mpic concurrency */ +#define KVM_MAX_VCPUS 4 +#define KVM_MAX_VCORES 4 +#else #define KVM_MAX_VCPUS NR_CPUS #define KVM_MAX_VCORES NR_CPUS +#endif #define KVM_USER_MEM_SLOTS 32 #define KVM_MEM_SLOTS_NUM KVM_USER_MEM_SLOTS -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
