From: Stefano Garzarella <firstname.lastname@example.org> To: 傅关丞 <email@example.com> Cc: "Michael S. Tsirkin" <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, Colin King <email@example.com>, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com Subject: Re: [External] Re: [PATCH 0/4] Add multi-cid support for vsock driver Date: Wed, 4 Aug 2021 17:23:49 +0200 [thread overview] Message-ID: <20210804152349.o4vh233xjdruh4pv@steredhat> (raw) In-Reply-To: <CAKv9dH5KbN25m8_Wmej9WXgJWheRV5S-tyPCdjUHHEFoWk-V1w@mail.gmail.com> On Wed, Aug 04, 2021 at 03:09:41PM +0800, 傅关丞 wrote: >Sorry I cannot figure out a good use case. > >It is normal for a host to have multiple ip addresses used for >communication. >So I thought it might be nice to have both host and guest use multiple >CIDs for communication. >I know this is not a very strong argument. Maybe there could be a use case for guests (which I don't see now), but for the host it seems pointless. The strength of vsock is that the guest knows that using CID=2 always reaches the host. Moreover we have recently merged VMADDR_FLAG_TO_HOST that when set allows you to forward any packet to the host, regardless of the CID (not yet supported by vhost-vsock). > >The vsock driver does not work if one of the two peers doesn't support >multiple CIDs. This is absolutely to be avoided. I think the virtio device feature negotiation can help here. > >I have a possible solution here, but there may be some problems with it >that I haven't noticed. > >Hypervisors will use different ways to send CIDs setup to the kernel based >on their vsock setup. > >------For host------- >If host vsock driver supports multi-cid, the hypervisor will use the >modified VHOST_VSOCK_SET_GUEST_CID call to set its CIDs. >Otherwise, the original call is used. > >------For guest------- >Now the virtio_vsock_config looks like this: >u64 guest_cid >u32 num_guest_cid; >u32 num_host_cid; >u32 index; >u64 cid; > >If the guest vsock driver supports multi-cid, it will read num_guest_cid >and num_host_cid from the device config space. >Then it writes an index register, which is the cid it wants to read. After >hypervisors handle this issue, it can read the cid >from the cid register. > >If it does not support multi-cid, it will just read the guest_cid from the >config space, which should work just fine. > Why not add a new device feature to enable or disable multi-cid? > >-------Communication-------- >For communication issues, we might need to use a new feature bit. Let's >call it VHOST_VSOCK_SUPPORT_MULTI_CID. >The basic idea is that this feature bit is set when both host and guest >support using multiple CIDs. After negotiation, if the feature bit >is set, the host can use all the CIDs specified to communicate with the >guest. Otherwise, the first cid passed in will >be used as the guest_cid to communicate with guests. I think the same feature bit can be used for the virtio_vsock_config, no? > >Also, if the bit is set for guests, all the CIDs can be used to communicate >with the host. Otherwise, the first cid with index 0 will be >used as the guest_cid while the VMADDR_HOST_CID will be used for host cid. We already have VMADDR_FLAG_TO_HOST to forward all packets to the host, we only need to support in some way in vhost-vsock. Thanks, Stefano
next prev parent reply other threads:[~2021-08-04 15:25 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-08-02 12:07 fuguancheng 2021-08-02 12:07 ` [PATCH 1/4] VSOCK DRIVER: Add multi-cid support for guest fuguancheng 2021-08-02 20:10 ` Michael S. Tsirkin 2021-08-02 20:11 ` Michael S. Tsirkin 2021-08-02 20:20 ` Michael S. Tsirkin 2021-08-02 12:07 ` [PATCH 2/4] VSOCK DRIVER: support communication using additional guest cid fuguancheng 2021-08-02 20:13 ` Michael S. Tsirkin 2021-08-02 12:07 ` [PATCH 3/4] VSOCK DRIVER: support specifying additional cids for host fuguancheng 2021-08-02 12:07 ` [PATCH 4/4] VSOCK DRIVER: support communication using host additional cids fuguancheng 2021-08-02 13:42 ` [PATCH 0/4] Add multi-cid support for vsock driver Stefano Garzarella [not found] ` <CAKv9dH5KbN25m8_Wmej9WXgJWheRV5S-tyPCdjUHHEFoWk-V1w@mail.gmail.com> 2021-08-04 15:23 ` Stefano Garzarella [this message] 2021-08-02 20:21 ` Michael S. Tsirkin
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