Messages in this thread Patch in this message | | | From | Bogdan Purcareata <> | Subject | [PATCH 2/2] powerpc/kvm: Limit MAX_VCPUS for guests running on RT Linux | Date | Wed, 18 Feb 2015 09:32:35 +0000 |
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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@freescale.com> Signed-off-by: Bogdan Purcareata <bogdan.purcareata@freescale.com> Reviewed-by: Scott Wood <scottwood@freescale.com> --- 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
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