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Tue, 12 Mar 2024 15:07:01 +0000 Received: from PH0PR10MB4664.namprd10.prod.outlook.com ([fe80::75a:a398:452a:90a9]) by PH0PR10MB4664.namprd10.prod.outlook.com ([fe80::75a:a398:452a:90a9%6]) with mapi id 15.20.7362.035; Tue, 12 Mar 2024 15:07:01 +0000 Message-ID: <37e871fa-6837-437f-acad-789fe466260b@oracle.com> Date: Tue, 12 Mar 2024 11:06:48 -0400 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 2/8] virtio-pci: Lock ioeventfd state with VIRTIO_F_NOTIFICATION_DATA Content-Language: en-US To: "Michael S. Tsirkin" Cc: Eugenio Perez Martin , qemu-devel@nongnu.org, jasowang@redhat.com, si-wei.liu@oracle.com, boris.ostrovsky@oracle.com, raphael@enfabrica.net, kwolf@redhat.com, hreitz@redhat.com, pasic@linux.ibm.com, borntraeger@linux.ibm.com, farman@linux.ibm.com, thuth@redhat.com, richard.henderson@linaro.org, david@redhat.com, iii@linux.ibm.com, cohuck@redhat.com, pbonzini@redhat.com, fam@euphon.net, stefanha@redhat.com, qemu-block@nongnu.org, qemu-s390x@nongnu.org, virtio-fs@lists.linux.dev References: <20240304194612.611660-1-jonah.palmer@oracle.com> <20240304194612.611660-3-jonah.palmer@oracle.com> <20240308115951-mutt-send-email-mst@kernel.org> <20240308141907-mutt-send-email-mst@kernel.org> <20240311114638-mutt-send-email-mst@kernel.org> <20240312105706-mutt-send-email-mst@kernel.org> From: Jonah Palmer In-Reply-To: <20240312105706-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: 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X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 3/12/24 10:58 AM, Michael S. Tsirkin wrote: > On Tue, Mar 12, 2024 at 10:33:51AM -0400, Jonah Palmer wrote: >> >> >> On 3/11/24 11:47 AM, Michael S. Tsirkin wrote: >>> On Mon, Mar 11, 2024 at 10:53:25AM -0400, Jonah Palmer wrote: >>>> >>>> >>>> On 3/8/24 2:19 PM, Michael S. Tsirkin wrote: >>>>> On Fri, Mar 08, 2024 at 12:45:13PM -0500, Jonah Palmer wrote: >>>>>> >>>>>> >>>>>> On 3/8/24 12:36 PM, Eugenio Perez Martin wrote: >>>>>>> On Fri, Mar 8, 2024 at 6: 01 PM Michael S. Tsirkin >>>>>>> wrote: > > On Mon, Mar 04, 2024 at 02: 46: 06PM -0500, Jonah Palmer >>>>>>> wrote: > > Prevent ioeventfd from being enabled/disabled when a >>>>>>> virtio-pci > > device >>>>>>> ZjQcmQRYFpfptBannerStart >>>>>>> This Message Is From an External Sender >>>>>>> This message came from outside your organization. >>>>>>> Report Suspicious >>>>>>> >>>>>>> ZjQcmQRYFpfptBannerEnd >>>>>>> >>>>>>> On Fri, Mar 8, 2024 at 6:01 PM Michael S. Tsirkin wrote: >>>>>>>> >>>>>>>> On Mon, Mar 04, 2024 at 02:46:06PM -0500, Jonah Palmer wrote: >>>>>>>>> Prevent ioeventfd from being enabled/disabled when a virtio-pci >>>>>>>>> device has negotiated the VIRTIO_F_NOTIFICATION_DATA transport >>>>>>>>> feature. >>>>>>>>> >>>>>>>>> Due to ioeventfd not being able to carry the extra data associated with >>>>>>>>> this feature, the ioeventfd should be left in a disabled state for >>>>>>>>> emulated virtio-pci devices using this feature. >>>>>>>>> >>>>>>>>> Reviewed-by: Eugenio Pérez >>>>>>>>> Signed-off-by: Jonah Palmer >>>>>>>> >>>>>>>> I thought hard about this. I propose that for now, >>>>>>>> instead of disabling ioevetfd silently we error out unless >>>>>>>> user disabled it for us. >>>>>>>> WDYT? >>>>>>>> >>>>>>> >>>>>>> Yes, error is a better plan than silently disabling it. In the >>>>>>> (unlikely?) case we are able to make notification data work with >>>>>>> eventfd in the future, it makes the change more evident. >>>>>>> >>>>>> >>>>>> Will do in v2. I assume we'll also make this the case for virtio-mmio and >>>>>> virtio-ccw? >>>>> >>>>> Guess so. Pls note freeze is imminent. >>>> >>>> Got it. Also, would you mind elaborating a bit more on "error out"? E.g. do >>>> we want to prevent the Qemu from starting at all if a device is attempting >>>> to use both VIRTIO_F_NOTIFICATION_DATA and ioeventfd? Or do you mean >>>> something like still keep ioeventfd disabled but also log an error message >>>> unless it was explicitly disabled by the user? >>> >>> >>> my preference would be to block device instance from being created. >>> >> >> I could very well be missing something here, but I was looking to see how I >> could block the device from being created (realized) given the functional >> mismatch between negotiating the VIRTIO_F_NOTIFICATION_DATA feature and >> ioeventfd being enabled. >> >> However, I realized that feature negotiation only happens after the virtio >> device has been realized and it's one of the last steps before the device >> becomes fully operational. In other words, we don't know if the guest >> (driver) also supports this feature until the feature negotiation phase, >> which is after realization. >> >> So, during realization (e.g. virtio_device_realize), we know if the virtio >> device (1) intends to negotiate the VIRTIO_F_NOTIFICATION_DATA feature and >> (2) has enabled ioeventfd, however, we don't know if the driver will >> actually support this notification data feature. >> >> Given this, we could block the device from being created if the device is >> *intending* to use the notification data feature along with ioeventfd, but >> this seems premature since we don't know if the feature will actually be >> successfully negotiated. > > Yes this is the option I had in mind. Many devices with this feature > do not actually work if they do not get the extra data > so they fail FEATURES_OK, anyway. > > Ah, okay I see. This was the extra context I was missing. Will do, thanks Michael! >> Another option might be check this during/immediately after feature >> negotiation, and then unrealize the device. However, I'm not sure if by this >> point it's "too late" to unrealize it. >> >> There's also other options like defaulting to using notification data over >> ioeventfd (since a user would need to explicitly enable it, showing intent >> to actually use the feature), which is what we're doing now, except we could >> add some kind of warning message for the user. Another option could be >> setting the device to broken. However, these options don't align with your >> suggestion of removing the device completely. >> >> Let me know how you'd like me to proceed with this. Thanks! >> >>>>>>>> >>>>>>>>> --- >>>>>>>>> hw/virtio/virtio-pci.c | 6 ++++-- >>>>>>>>> 1 file changed, 4 insertions(+), 2 deletions(-) >>>>>>>>> >>>>>>>>> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c >>>>>>>>> index d12edc567f..287b8f7720 100644 >>>>>>>>> --- a/hw/virtio/virtio-pci.c >>>>>>>>> +++ b/hw/virtio/virtio-pci.c >>>>>>>>> @@ -417,13 +417,15 @@ static void virtio_ioport_write(void *opaque, uint32_t addr, uint32_t val) >>>>>>>>> } >>>>>>>>> break; >>>>>>>>> case VIRTIO_PCI_STATUS: >>>>>>>>> - if (!(val & VIRTIO_CONFIG_S_DRIVER_OK)) { >>>>>>>>> + if (!(val & VIRTIO_CONFIG_S_DRIVER_OK) && >>>>>>>>> + !virtio_vdev_has_feature(vdev, VIRTIO_F_NOTIFICATION_DATA)) { >>>>>>>>> virtio_pci_stop_ioeventfd(proxy); >>>>>>>>> } >>>>>>>>> >>>>>>>>> virtio_set_status(vdev, val & 0xFF); >>>>>>>>> >>>>>>>>> - if (val & VIRTIO_CONFIG_S_DRIVER_OK) { >>>>>>>>> + if ((val & VIRTIO_CONFIG_S_DRIVER_OK) && >>>>>>>>> + !virtio_vdev_has_feature(vdev, VIRTIO_F_NOTIFICATION_DATA)) { >>>>>>>>> virtio_pci_start_ioeventfd(proxy); >>>>>>>>> } >>>>>>>>> >>>>>>>>> -- >>>>>>>>> 2.39.3 >>>>>>>> >>>>>>> >>>>> >>> >