From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-dev-return-5251-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 9676D985DA4 for ; Fri, 4 Jan 2019 12:49:04 +0000 (UTC) Date: Fri, 4 Jan 2019 13:48:55 +0100 From: Cornelia Huck Message-ID: <20190104134855.72418c51.cohuck@redhat.com> In-Reply-To: <20190103182849.7b0b0f0b@oc2783563651> References: <20190103160804.21438-1-cohuck@redhat.com> <20190103160804.21438-3-cohuck@redhat.com> <20190103182849.7b0b0f0b@oc2783563651> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: [virtio-dev] Re: [PATCH 2/2] virtio: document virtio_config_ops restrictions To: Halil Pasic Cc: "Michael S . Tsirkin" , Jason Wang , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, virtio-dev@lists.oasis-open.org, Wei Wang List-ID: On Thu, 3 Jan 2019 18:28:49 +0100 Halil Pasic wrote: > On Thu, 3 Jan 2019 17:08:04 +0100 > Cornelia Huck wrote: > > > Some transports (e.g. virtio-ccw) implement virtio operations that > > seem to be a simple read/write as something more involved that > > cannot be done from an atomic context. > > > > Give at least a hint about that. > > > > Signed-off-by: Cornelia Huck > > --- > > include/linux/virtio_config.h | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h > > index 7087ef946ba7..987b6491b946 100644 > > --- a/include/linux/virtio_config.h > > +++ b/include/linux/virtio_config.h > > @@ -12,6 +12,11 @@ struct irq_affinity; > > > > /** > > * virtio_config_ops - operations for configuring a virtio device > > + * Note: Do not assume that a transport implements all of the operations > > + * getting/setting a value as a simple read/write! Generally speaking, > > + * any of @get/@set, @get_status/@set_status, or @get_features/ > > + * @finalize_features are NOT safe to be called from an atomic > > + * context. > > I think the only exception is @bus_name (and maybe @generation, I don't > know) because it does not have to 'speak' with the hypervisor. If a > transport operation has to 'speak' with the hypervisor, we do it by > making it interpret a channel program. That means not safe to be called > form atomic context. Or am I missing something? I explicitly singled out the listed callbacks because they read/write a value and there might be more to them than meets the eye. I would assume that nobody expects calling e.g. find_vqs (allocating queues) from an atomic context to be a good idea :) Maybe I should do s/Generally speaking/In particular/ ? That said, it's only a hint; we should add might_sleep as well to interfaces where it makes sense. --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org From mboxrd@z Thu Jan 1 00:00:00 1970 From: Cornelia Huck Subject: Re: [PATCH 2/2] virtio: document virtio_config_ops restrictions Date: Fri, 4 Jan 2019 13:48:55 +0100 Message-ID: <20190104134855.72418c51.cohuck@redhat.com> References: <20190103160804.21438-1-cohuck@redhat.com> <20190103160804.21438-3-cohuck@redhat.com> <20190103182849.7b0b0f0b@oc2783563651> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190103182849.7b0b0f0b@oc2783563651> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Halil Pasic Cc: virtio-dev@lists.oasis-open.org, "Michael S . Tsirkin" , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On Thu, 3 Jan 2019 18:28:49 +0100 Halil Pasic wrote: > On Thu, 3 Jan 2019 17:08:04 +0100 > Cornelia Huck wrote: > > > Some transports (e.g. virtio-ccw) implement virtio operations that > > seem to be a simple read/write as something more involved that > > cannot be done from an atomic context. > > > > Give at least a hint about that. > > > > Signed-off-by: Cornelia Huck > > --- > > include/linux/virtio_config.h | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h > > index 7087ef946ba7..987b6491b946 100644 > > --- a/include/linux/virtio_config.h > > +++ b/include/linux/virtio_config.h > > @@ -12,6 +12,11 @@ struct irq_affinity; > > > > /** > > * virtio_config_ops - operations for configuring a virtio device > > + * Note: Do not assume that a transport implements all of the operations > > + * getting/setting a value as a simple read/write! Generally speaking, > > + * any of @get/@set, @get_status/@set_status, or @get_features/ > > + * @finalize_features are NOT safe to be called from an atomic > > + * context. > > I think the only exception is @bus_name (and maybe @generation, I don't > know) because it does not have to 'speak' with the hypervisor. If a > transport operation has to 'speak' with the hypervisor, we do it by > making it interpret a channel program. That means not safe to be called > form atomic context. Or am I missing something? I explicitly singled out the listed callbacks because they read/write a value and there might be more to them than meets the eye. I would assume that nobody expects calling e.g. find_vqs (allocating queues) from an atomic context to be a good idea :) Maybe I should do s/Generally speaking/In particular/ ? That said, it's only a hint; we should add might_sleep as well to interfaces where it makes sense.