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Subject: Re: [virtio-comment] Re: [PATCH 00/11] Introduce transitional mmr pci device
On Wed, Apr 12, 2023 at 05:15:40AM +0000, Parav Pandit wrote: > > > > From: virtio-comment@lists.oasis-open.org <virtio-comment@lists.oasis- > > open.org> On Behalf Of Michael S. Tsirkin > > > New issue I found today: > > - if guest disables MSI-X host can not disable MSI-X. > > need some other channel to notify device about this. > > > I will look into it. > > > Old issues we discussed before today: > > - reset needs some special handling because real hardware > > can not guarantee returning 0 on the 1st read > When done through the legacy MMR as we discussed, it will. > > > - if guest writes into mac, reusing host mac (which is RO) > > will not work, need extra registers > No. Again legacy interface section of MMR behaves as legacy. > > > - something about notification makes you want to poke > > at modern notification register? which of course > > is its own can of worms with VIRTIO_F_NOTIFICATION_DATA > > changing the format completely. > There is no NOTIFICATION_DATA with legacy. So it is not applicable. > Format is same with only vq index. You are writing into modern register here. *what* are you writing there? with modern register the format depends on features. here you did not negotiate any features. what if NOTIFICATION_DATA is a required feature? with legacy there's no FEATURES_OK so no way to report failure. driver barrels on, sends wrong data in the kick and hangs. Sure, we can add a section to notification register and come up with some behaviour. Without even trying to guess how messy or clean that will be, far from being a small clean contained thing this feature is sticking its fingers in lots of pies. Look I know proposed this originally. I thought it's a small thing too. It was an idea. I am not sure it pans out though. Not all ideas work. -- MST
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