Re: [RFC PATCH 3/4] PCI: endpoint: Introduce virtio library for EP functions

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Feb 03, 2023 at 07:04:17PM +0900, Shunsuke Mie wrote:
> Add a new library to access a virtio ring located on PCIe host memory. The
> library generates struct pci_epf_vringh that is introduced in this patch.
> The struct has a vringh member, so vringh APIs can be used to access the
> virtio ring.
> 
> Signed-off-by: Shunsuke Mie <mie@igel.co.jp>
> Signed-off-by: Takanari Hayama <taki@igel.co.jp>
> ---
>  drivers/pci/endpoint/Kconfig          |   7 ++
>  drivers/pci/endpoint/Makefile         |   1 +
>  drivers/pci/endpoint/pci-epf-virtio.c | 113 ++++++++++++++++++++++++++
>  include/linux/pci-epf-virtio.h        |  25 ++++++
>  4 files changed, 146 insertions(+)
>  create mode 100644 drivers/pci/endpoint/pci-epf-virtio.c
>  create mode 100644 include/linux/pci-epf-virtio.h
> 
> diff --git a/drivers/pci/endpoint/Kconfig b/drivers/pci/endpoint/Kconfig
> index 17bbdc9bbde0..07276dcc43c8 100644
> --- a/drivers/pci/endpoint/Kconfig
> +++ b/drivers/pci/endpoint/Kconfig
> @@ -28,6 +28,13 @@ config PCI_ENDPOINT_CONFIGFS
>  	   configure the endpoint function and used to bind the
>  	   function with a endpoint controller.
>  
> +config PCI_ENDPOINT_VIRTIO
> +	tristate
> +	depends on PCI_ENDPOINT
> +	select VHOST_IOMEM
> +	help
> +	  TODO update this comment
> +
>  source "drivers/pci/endpoint/functions/Kconfig"
>  
>  endmenu
> diff --git a/drivers/pci/endpoint/Makefile b/drivers/pci/endpoint/Makefile
> index 95b2fe47e3b0..95712f0a13d1 100644
> --- a/drivers/pci/endpoint/Makefile
> +++ b/drivers/pci/endpoint/Makefile
> @@ -4,5 +4,6 @@
>  #
>  
>  obj-$(CONFIG_PCI_ENDPOINT_CONFIGFS)	+= pci-ep-cfs.o
> +obj-$(CONFIG_PCI_ENDPOINT_VIRTIO)	+= pci-epf-virtio.o
>  obj-$(CONFIG_PCI_ENDPOINT)		+= pci-epc-core.o pci-epf-core.o\
>  					   pci-epc-mem.o functions/
> diff --git a/drivers/pci/endpoint/pci-epf-virtio.c b/drivers/pci/endpoint/pci-epf-virtio.c
> new file mode 100644
> index 000000000000..7134ca407a03
> --- /dev/null
> +++ b/drivers/pci/endpoint/pci-epf-virtio.c
> @@ -0,0 +1,113 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Virtio library for PCI Endpoint function
> + */
> +#include <linux/kernel.h>
> +#include <linux/pci-epf-virtio.h>
> +#include <linux/pci-epc.h>
> +#include <linux/virtio_pci.h>
> +
> +static void __iomem *epf_virtio_map_vq(struct pci_epf *epf, u32 pfn,
> +				       size_t size, phys_addr_t *vq_phys)
> +{
> +	int err;
> +	phys_addr_t vq_addr;
> +	size_t vq_size;
> +	void __iomem *vq_virt;
> +
> +	vq_addr = (phys_addr_t)pfn << VIRTIO_PCI_QUEUE_ADDR_SHIFT;
> +
> +	vq_size = vring_size(size, VIRTIO_PCI_VRING_ALIGN) + 100;

100?

Also ugh, this uses the legacy vring_size.
Did not look closely but is all this limited to legacy virtio then?
Pls make sure you code builds with #define VIRTIO_RING_NO_LEGACY.

> +
> +	vq_virt = pci_epc_mem_alloc_addr(epf->epc, vq_phys, vq_size);
> +	if (!vq_virt) {
> +		pr_err("Failed to allocate epc memory\n");
> +		return ERR_PTR(-ENOMEM);
> +	}
> +
> +	err = pci_epc_map_addr(epf->epc, epf->func_no, epf->vfunc_no, *vq_phys,
> +			       vq_addr, vq_size);
> +	if (err) {
> +		pr_err("Failed to map virtuqueue to local");
> +		goto err_free;
> +	}
> +
> +	return vq_virt;
> +
> +err_free:
> +	pci_epc_mem_free_addr(epf->epc, *vq_phys, vq_virt, vq_size);
> +
> +	return ERR_PTR(err);
> +}
> +
> +static void epf_virtio_unmap_vq(struct pci_epf *epf, void __iomem *vq_virt,
> +				phys_addr_t vq_phys, size_t size)
> +{
> +	pci_epc_unmap_addr(epf->epc, epf->func_no, epf->vfunc_no, vq_phys);
> +	pci_epc_mem_free_addr(epf->epc, vq_phys, vq_virt,
> +			      vring_size(size, VIRTIO_PCI_VRING_ALIGN));
> +}
> +
> +/**
> + * pci_epf_virtio_alloc_vringh() - allocate epf vringh from @pfn
> + * @epf: the EPF device that communicates to host virtio dirver
> + * @features: the virtio features of device
> + * @pfn: page frame number of virtqueue located on host memory. It is
> + *		passed during virtqueue negotiation.
> + * @size: a length of virtqueue
> + */
> +struct pci_epf_vringh *pci_epf_virtio_alloc_vringh(struct pci_epf *epf,
> +						   u64 features, u32 pfn,
> +						   size_t size)
> +{
> +	int err;
> +	struct vring vring;
> +	struct pci_epf_vringh *evrh;
> +
> +	evrh = kmalloc(sizeof(*evrh), GFP_KERNEL);
> +	if (!evrh) {
> +		err = -ENOMEM;
> +		goto err_unmap_vq;
> +	}
> +
> +	evrh->size = size;
> +
> +	evrh->virt = epf_virtio_map_vq(epf, pfn, size, &evrh->phys);
> +	if (IS_ERR(evrh->virt))
> +		return evrh->virt;
> +
> +	vring_init(&vring, size, evrh->virt, VIRTIO_PCI_VRING_ALIGN);
> +
> +	err = vringh_init_iomem(&evrh->vrh, features, size, false, GFP_KERNEL,
> +				vring.desc, vring.avail, vring.used);
> +	if (err)
> +		goto err_free_epf_vq;
> +
> +	return evrh;
> +
> +err_free_epf_vq:
> +	kfree(evrh);
> +
> +err_unmap_vq:
> +	epf_virtio_unmap_vq(epf, evrh->virt, evrh->phys, evrh->size);
> +
> +	return ERR_PTR(err);
> +}
> +EXPORT_SYMBOL_GPL(pci_epf_virtio_alloc_vringh);
> +
> +/**
> + * pci_epf_virtio_free_vringh() - release allocated epf vring
> + * @epf: the EPF device that communicates to host virtio dirver
> + * @evrh: epf vringh to free
> + */
> +void pci_epf_virtio_free_vringh(struct pci_epf *epf,
> +				struct pci_epf_vringh *evrh)
> +{
> +	epf_virtio_unmap_vq(epf, evrh->virt, evrh->phys, evrh->size);
> +	kfree(evrh);
> +}
> +EXPORT_SYMBOL_GPL(pci_epf_virtio_free_vringh);
> +
> +MODULE_DESCRIPTION("PCI EP Virtio Library");
> +MODULE_AUTHOR("Shunsuke Mie <mie@igel.co.jp>");
> +MODULE_LICENSE("GPL");
> diff --git a/include/linux/pci-epf-virtio.h b/include/linux/pci-epf-virtio.h
> new file mode 100644
> index 000000000000..ae09087919a9
> --- /dev/null
> +++ b/include/linux/pci-epf-virtio.h
> @@ -0,0 +1,25 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * PCI Endpoint Function (EPF) for virtio definitions
> + */
> +#ifndef __LINUX_PCI_EPF_VIRTIO_H
> +#define __LINUX_PCI_EPF_VIRTIO_H
> +
> +#include <linux/types.h>
> +#include <linux/vringh.h>
> +#include <linux/pci-epf.h>
> +
> +struct pci_epf_vringh {
> +	struct vringh vrh;
> +	void __iomem *virt;
> +	phys_addr_t phys;
> +	size_t size;
> +};
> +
> +struct pci_epf_vringh *pci_epf_virtio_alloc_vringh(struct pci_epf *epf,
> +						   u64 features, u32 pfn,
> +						   size_t size);
> +void pci_epf_virtio_free_vringh(struct pci_epf *epf,
> +				struct pci_epf_vringh *evrh);
> +
> +#endif // __LINUX_PCI_EPF_VIRTIO_H
> -- 
> 2.25.1