| Message ID | 20170215220048.3423-3-pbonzini@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
2017-02-15 23:00+0100, Paolo Bonzini: > This will make it easier to support multiple address spaces in > kvm_gfn_to_hva_cache_init. Instead of having to check the address > space id, we can keep on checking just the generation number. > > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> > --- Reviewed-by: Radim Krčmař <rkrcmar@redhat.com> > virt/kvm/kvm_main.c | 24 ++++++++++++++++-------- > 1 file changed, 16 insertions(+), 8 deletions(-) > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index e21bac7ed5d3..a83c186cefc1 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -506,11 +506,6 @@ static struct kvm_memslots *kvm_alloc_memslots(void) > if (!slots) > return NULL; > > - /* > - * Init kvm generation close to the maximum to easily test the > - * code of handling generation number wrap-around. > - */ > - slots->generation = -150; > for (i = 0; i < KVM_MEM_SLOTS_NUM; i++) > slots->id_to_index[i] = slots->memslots[i].id = i; > > @@ -641,9 +636,16 @@ static struct kvm *kvm_create_vm(unsigned long type) > > r = -ENOMEM; > for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) { > - kvm->memslots[i] = kvm_alloc_memslots(); > - if (!kvm->memslots[i]) > + struct kvm_memslots *slots = kvm_alloc_memslots(); > + if (!slots) > goto out_err_no_srcu; > + /* > + * Generations must be different for each address space. > + * Init kvm generation close to the maximum to easily test the > + * code of handling generation number wrap-around. > + */ > + slots->generation = i * 2 - 150; > + rcu_assign_pointer(kvm->memslots[i], slots); > } > > if (init_srcu_struct(&kvm->srcu)) > @@ -870,8 +872,14 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm, > * Increment the new memslot generation a second time. This prevents > * vm exits that race with memslot updates from caching a memslot > * generation that will (potentially) be valid forever. > + * > + * Generations must be unique even across address spaces. We do not need > + * a global counter for that, instead the generation space is evenly split > + * across address spaces. For example, with two address spaces, address > + * space 0 will use generations 0, 4, 8, ... while * address space 1 will > + * use generations 2, 6, 10, 14, ... > */ > - slots->generation++; > + slots->generation += KVM_ADDRESS_SPACE_NUM * 2 - 1; > > kvm_arch_memslots_updated(kvm, slots); > > -- > 1.8.3.1 > >
Paolo Bonzini <pbonzini@redhat.com> writes: > This will make it easier to support multiple address spaces in > kvm_gfn_to_hva_cache_init. Instead of having to check the address > space id, we can keep on checking just the generation number. > > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> > --- > virt/kvm/kvm_main.c | 24 ++++++++++++++++-------- > 1 file changed, 16 insertions(+), 8 deletions(-) > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index e21bac7ed5d3..a83c186cefc1 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -506,11 +506,6 @@ static struct kvm_memslots *kvm_alloc_memslots(void) > if (!slots) > return NULL; > > - /* > - * Init kvm generation close to the maximum to easily test the > - * code of handling generation number wrap-around. > - */ > - slots->generation = -150; > for (i = 0; i < KVM_MEM_SLOTS_NUM; i++) > slots->id_to_index[i] = slots->memslots[i].id = i; > > @@ -641,9 +636,16 @@ static struct kvm *kvm_create_vm(unsigned long type) > > r = -ENOMEM; > for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) { > - kvm->memslots[i] = kvm_alloc_memslots(); > - if (!kvm->memslots[i]) > + struct kvm_memslots *slots = kvm_alloc_memslots(); > + if (!slots) > goto out_err_no_srcu; > + /* > + * Generations must be different for each address space. > + * Init kvm generation close to the maximum to easily test the > + * code of handling generation number wrap-around. > + */ > + slots->generation = i * 2 - 150; > + rcu_assign_pointer(kvm->memslots[i], slots); > } I can't seem to understand why rcu_assign_pointer wasn't used before. kvm->memslots[i] was a rcu protected pointer even before this change, right ? > if (init_srcu_struct(&kvm->srcu)) > @@ -870,8 +872,14 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm, > * Increment the new memslot generation a second time. This prevents > * vm exits that race with memslot updates from caching a memslot > * generation that will (potentially) be valid forever. > + * > + * Generations must be unique even across address spaces. We do not need > + * a global counter for that, instead the generation space is evenly split > + * across address spaces. For example, with two address spaces, address > + * space 0 will use generations 0, 4, 8, ... while * address space 1 will > + * use generations 2, 6, 10, 14, ... > */ > - slots->generation++; > + slots->generation += KVM_ADDRESS_SPACE_NUM * 2 - 1; > > kvm_arch_memslots_updated(kvm, slots);
> > + /* > > + * Generations must be different for each address space. > > + * Init kvm generation close to the maximum to easily test the > > + * code of handling generation number wrap-around. > > + */ > > + slots->generation = i * 2 - 150; > > + rcu_assign_pointer(kvm->memslots[i], slots); > > } > > I can't seem to understand why rcu_assign_pointer wasn't used before. > kvm->memslots[i] was a rcu protected pointer even before this change, > right ? Actually, a better match is RCU_INIT_POINTER. Here there is no concurrent reader because we're just initializing the struct kvm. There is something else providing synchronization between this writer and the "first" RCU read-side. It could be signaling a condition variable, creating a thread, or releasing a mutex; all three of them have release semantics, which means they imply a smp_wmb just like rcu_assign_pointer does. Paolo > > if (init_srcu_struct(&kvm->srcu)) > > @@ -870,8 +872,14 @@ static struct kvm_memslots > > *install_new_memslots(struct kvm *kvm, > > * Increment the new memslot generation a second time. This prevents > > * vm exits that race with memslot updates from caching a memslot > > * generation that will (potentially) be valid forever. > > + * > > + * Generations must be unique even across address spaces. We do not need > > + * a global counter for that, instead the generation space is evenly > > split > > + * across address spaces. For example, with two address spaces, address > > + * space 0 will use generations 0, 4, 8, ... while * address space 1 will > > + * use generations 2, 6, 10, 14, ... > > */ > > - slots->generation++; > > + slots->generation += KVM_ADDRESS_SPACE_NUM * 2 - 1; > > > > kvm_arch_memslots_updated(kvm, slots); >
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index e21bac7ed5d3..a83c186cefc1 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -506,11 +506,6 @@ static struct kvm_memslots *kvm_alloc_memslots(void) if (!slots) return NULL; - /* - * Init kvm generation close to the maximum to easily test the - * code of handling generation number wrap-around. - */ - slots->generation = -150; for (i = 0; i < KVM_MEM_SLOTS_NUM; i++) slots->id_to_index[i] = slots->memslots[i].id = i; @@ -641,9 +636,16 @@ static struct kvm *kvm_create_vm(unsigned long type) r = -ENOMEM; for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) { - kvm->memslots[i] = kvm_alloc_memslots(); - if (!kvm->memslots[i]) + struct kvm_memslots *slots = kvm_alloc_memslots(); + if (!slots) goto out_err_no_srcu; + /* + * Generations must be different for each address space. + * Init kvm generation close to the maximum to easily test the + * code of handling generation number wrap-around. + */ + slots->generation = i * 2 - 150; + rcu_assign_pointer(kvm->memslots[i], slots); } if (init_srcu_struct(&kvm->srcu)) @@ -870,8 +872,14 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm, * Increment the new memslot generation a second time. This prevents * vm exits that race with memslot updates from caching a memslot * generation that will (potentially) be valid forever. + * + * Generations must be unique even across address spaces. We do not need + * a global counter for that, instead the generation space is evenly split + * across address spaces. For example, with two address spaces, address + * space 0 will use generations 0, 4, 8, ... while * address space 1 will + * use generations 2, 6, 10, 14, ... */ - slots->generation++; + slots->generation += KVM_ADDRESS_SPACE_NUM * 2 - 1; kvm_arch_memslots_updated(kvm, slots);
This will make it easier to support multiple address spaces in kvm_gfn_to_hva_cache_init. Instead of having to check the address space id, we can keep on checking just the generation number. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> --- virt/kvm/kvm_main.c | 24 ++++++++++++++++-------- 1 file changed, 16 insertions(+), 8 deletions(-)