> -----Original Message----- > From: Will Deacon [mailto:will@xxxxxxxxxx] > Sent: 03 August 2021 12:41 > To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@xxxxxxxxxx> > Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; kvmarm@xxxxxxxxxxxxxxxxxxxxx; > linux-kernel@xxxxxxxxxxxxxxx; maz@xxxxxxxxxx; catalin.marinas@xxxxxxx; > james.morse@xxxxxxx; julien.thierry.kdev@xxxxxxxxx; > suzuki.poulose@xxxxxxx; jean-philippe@xxxxxxxxxx; > Alexandru.Elisei@xxxxxxx; qperret@xxxxxxxxxx; Linuxarm > <linuxarm@xxxxxxxxxx> > Subject: Re: [PATCH v3 4/4] KVM: arm64: Clear active_vmids on vCPU > schedule out > > On Thu, Jul 29, 2021 at 11:40:09AM +0100, Shameer Kolothum wrote: > > Like ASID allocator, we copy the active_vmids into the > > reserved_vmids on a rollover. But it's unlikely that > > every CPU will have a vCPU as current task and we may > > end up unnecessarily reserving the VMID space. > > > > Hence, clear active_vmids when scheduling out a vCPU. > > > > Suggested-by: Will Deacon <will@xxxxxxxxxx> > > Signed-off-by: Shameer Kolothum > <shameerali.kolothum.thodi@xxxxxxxxxx> > > --- > > arch/arm64/include/asm/kvm_host.h | 1 + > > arch/arm64/kvm/arm.c | 1 + > > arch/arm64/kvm/vmid.c | 6 ++++++ > > 3 files changed, 8 insertions(+) > > > > diff --git a/arch/arm64/include/asm/kvm_host.h > b/arch/arm64/include/asm/kvm_host.h > > index bb993bce1363..d93141cb8d16 100644 > > --- a/arch/arm64/include/asm/kvm_host.h > > +++ b/arch/arm64/include/asm/kvm_host.h > > @@ -687,6 +687,7 @@ extern unsigned int kvm_arm_vmid_bits; > > int kvm_arm_vmid_alloc_init(void); > > void kvm_arm_vmid_alloc_free(void); > > void kvm_arm_vmid_update(struct kvm_vmid *kvm_vmid); > > +void kvm_arm_vmid_clear_active(void); > > > > static inline void kvm_arm_pvtime_vcpu_init(struct kvm_vcpu_arch > *vcpu_arch) > > { > > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > > index 077e55a511a9..b134a1b89c84 100644 > > --- a/arch/arm64/kvm/arm.c > > +++ b/arch/arm64/kvm/arm.c > > @@ -435,6 +435,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) > > kvm_timer_vcpu_put(vcpu); > > kvm_vgic_put(vcpu); > > kvm_vcpu_pmu_restore_host(vcpu); > > + kvm_arm_vmid_clear_active(); > > > > vcpu->cpu = -1; > > } > > diff --git a/arch/arm64/kvm/vmid.c b/arch/arm64/kvm/vmid.c > > index 5584e84aed95..5fd51f5445c1 100644 > > --- a/arch/arm64/kvm/vmid.c > > +++ b/arch/arm64/kvm/vmid.c > > @@ -116,6 +116,12 @@ static u64 new_vmid(struct kvm_vmid > *kvm_vmid) > > return idx2vmid(vmid) | generation; > > } > > > > +/* Call with preemption disabled */ > > +void kvm_arm_vmid_clear_active(void) > > +{ > > + atomic64_set(this_cpu_ptr(&active_vmids), 0); > > +} > > I think this is very broken, as it will force everybody to take the > slow-path when they see an active_vmid of 0. Yes. I have seen that happening in my test setup. > It also doesn't solve the issue I mentioned before, as an active_vmid of 0 > means that the reserved vmid is preserved. > > Needs more thought... How about we clear all the active_vmids in kvm_arch_free_vm() if it matches the kvm_vmid->id ? But we may have to hold the lock there. Thanks, Shameer _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
