linux-kernel - Re: refactor the i915 GVT support

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Date:   Tue, 27 Jul 2021 09:12:24 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Gerd Hoffmann <kraxel@...hat.com>
Cc:     "Wang, Zhi A" <zhi.a.wang@...el.com>,
        Christoph Hellwig <hch@....de>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        "Vivi, Rodrigo" <rodrigo.vivi@...el.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: refactor the i915 GVT support

On Thu, Jul 22, 2021 at 01:26:36PM +0200, Gerd Hoffmann wrote:
>   Hi,
> 
> > https://github.com/intel/gvt-linux/blob/topic/gvt-xengt/drivers/gpu/drm/i915/gvt/xengt.c
> 
> > But it's hard for some customers to contribute their own "hypervisor"
> > module to the upstream Linux kernel. I am thinking what would be a
> > better solution here? The MPT layer in the kernel helps a lot for
> > customers, but only one open-source "hypervisor" module is there in
> > the kernel. That can confuse people which don't know the story.  One
> > thing I was thinking is to put a document about the background and
> > more description in the MPT headers. So it won't confuse more people. 
> 
> Getting the xengt module linked above merged into mainline
> would also nicely explain why there are hypervisor modules.

It would also be nice to explain why a GPU driver needs a hypervisor
specific shim like this in the first place.

        enum hypervisor_type type;
        int (*host_init)(struct device *dev, void *gvt, const void *ops);
        void (*host_exit)(struct device *dev, void *gvt);
        int (*attach_vgpu)(void *vgpu, unsigned long *handle);
        void (*detach_vgpu)(void *vgpu);

Doesn't vfio provide all this generically with notifiers?

        int (*inject_msi)(unsigned long handle, u32 addr, u16 data);

Isn't this one just an eventfd?

        unsigned long (*from_virt_to_mfn)(void *p);
        int (*read_gpa)(unsigned long handle, unsigned long gpa, void *buf,
                        unsigned long len);
        int (*write_gpa)(unsigned long handle, unsigned long gpa, void *buf,
                         unsigned long len);
        unsigned long (*gfn_to_mfn)(unsigned long handle, unsigned long gfn);

        int (*dma_map_guest_page)(unsigned long handle, unsigned long gfn,
                                  unsigned long size, dma_addr_t *dma_addr);
        void (*dma_unmap_guest_page)(unsigned long handle, dma_addr_t dma_addr);

        int (*dma_pin_guest_page)(unsigned long handle, dma_addr_t dma_addr);

        int (*map_gfn_to_mfn)(unsigned long handle, unsigned long gfn,
                              unsigned long mfn, unsigned int nr, bool map);
        bool (*is_valid_gfn)(unsigned long handle, unsigned long gfn);

Shouldn't the vfio page SW IOMMU do all of this generically?

        int (*enable_page_track)(unsigned long handle, u64 gfn);
        int (*disable_page_track)(unsigned long handle, u64 gfn);
        int (*set_trap_area)(unsigned long handle, u64 start, u64 end,
                             bool map);
        int (*set_opregion)(void *vgpu);
        int (*set_edid)(void *vgpu, int port_num);

edid depends on hypervisor??

        int (*get_vfio_device)(void *vgpu);
        void (*put_vfio_device)(void *vgpu);

Jason