On 18.02.15 10:32, Bogdan Purcareata wrote: > 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.cara...@freescale.com> > Signed-off-by: Bogdan Purcareata <bogdan.purcare...@freescale.com> > Reviewed-by: Scott Wood <scottw...@freescale.com>
I don't think this patch is reasonable to take upstream. If we have a latency issue, whoever spawned KVM VMs made a decision to spawn such big VMs. I'd say let's leave it at MAX_VCPUS == NR_CPUS for now and rather get someone to resolve any locking problems for real ;). Alex > --- > 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 > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
