netdev - RE: [PATCH net-next 16/19] net/mlx5: Implement dma ops and params for mediated device

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Message-ID: <AM0PR05MB486634DCB2778C2DFDBF752FD1780@AM0PR05MB4866.eurprd05.prod.outlook.com>
Date:   Thu, 7 Nov 2019 21:30:41 +0000
From:   Parav Pandit <parav@...lanox.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
CC:     "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Saeed Mahameed <saeedm@...lanox.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "leon@...nel.org" <leon@...nel.org>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        Jiri Pirko <jiri@...lanox.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>
Subject: RE: [PATCH net-next 16/19] net/mlx5: Implement dma ops and params for
 mediated device



> -----Original Message-----
> From: kvm-owner@...r.kernel.org <kvm-owner@...r.kernel.org> On Behalf
> Of Jakub Kicinski
> Sent: Thursday, November 7, 2019 2:43 PM
> To: Parav Pandit <parav@...lanox.com>
> Cc: alex.williamson@...hat.com; davem@...emloft.net;
> kvm@...r.kernel.org; netdev@...r.kernel.org; Saeed Mahameed
> <saeedm@...lanox.com>; kwankhede@...dia.com; leon@...nel.org;
> cohuck@...hat.com; Jiri Pirko <jiri@...lanox.com>; linux-
> rdma@...r.kernel.org
> Subject: Re: [PATCH net-next 16/19] net/mlx5: Implement dma ops and params
> for mediated device
> 
> On Thu,  7 Nov 2019 10:08:31 -0600, Parav Pandit wrote:
> > Implement dma ops wrapper to divert dma ops to its parent PCI device
> > because Intel IOMMU (and may be other IOMMU) is limited to PCI devices.
> >
> > Reviewed-by: Saeed Mahameed <saeedm@...lanox.com>
> > Signed-off-by: Parav Pandit <parav@...lanox.com>
> 
> Isn't this supposed to use PASSID or whatnot? Could you explain a little? This
> mdev stuff is pretty new to networking folks..

Currently series doesn't support PCI PASID.
While doing dma mapping, Intel IOMMU expects dma device to be PCI device in few function traces like, find_or_alloc_domain(), 
Since mdev bus is not a PCI bus, DMA mapping needs to go through its parent PCI device.
Otherwise dma ops on mdev devices fails, as I think it fails to identify how to perform the translations.
(It doesn't seem to consult its parent device).