Re: [RFC 04/13] vfio: introduce vfio-cxl core preludes

[Alex Williamson <alex.williamson@redhat.com>]

On Fri, 20 Sep 2024 15:34:37 -0700
Zhi Wang <zhiw@nvidia.com> wrote:

> In VFIO, common functions that used by VFIO variant drivers are managed
> in a set of "core" functions. E.g. the vfio-pci-core provides the common
> functions used by VFIO variant drviers to support PCI device
> passhthrough.
> 
> Although the CXL type-2 device has a PCI-compatible interface for device
> configuration and programming, they still needs special handlings when
> initialize the device:
> 
> - Probing the CXL DVSECs in the configuration.
> - Probing the CXL register groups implemented by the device.
> - Configuring the CXL device state required by the kernel CXL core.
> - Create the CXL region.
> - Special handlings of the CXL MMIO BAR.
> 
> Introduce vfio-cxl core predules to hold all the common functions used

s/predules/preludes/

> by VFIO variant drivers to support CXL device passthrough.
> 
> Signed-off-by: Zhi Wang <zhiw@nvidia.com>
> ---
>  drivers/vfio/pci/Kconfig         |   4 +
>  drivers/vfio/pci/Makefile        |   3 +
>  drivers/vfio/pci/vfio_cxl_core.c | 264 +++++++++++++++++++++++++++++++
>  include/linux/vfio_pci_core.h    |  37 +++++
>  4 files changed, 308 insertions(+)
>  create mode 100644 drivers/vfio/pci/vfio_cxl_core.c
> 
> diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
> index bf50ffa10bde..2196e79b132b 100644
> --- a/drivers/vfio/pci/Kconfig
> +++ b/drivers/vfio/pci/Kconfig
> @@ -7,6 +7,10 @@ config VFIO_PCI_CORE
>  	select VFIO_VIRQFD
>  	select IRQ_BYPASS_MANAGER
>  
> +config VFIO_CXL_CORE
> +	tristate
> +	select VFIO_PCI_CORE

I don't see anything in this series that depends on CXL Kconfigs, so it
seems this will break in randconfig when the resulting vfio-cxl variant
driver is enabled without core CXL support.

> +
>  config VFIO_PCI_MMAP
>  	def_bool y if !S390
>  	depends on VFIO_PCI_CORE
> diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
> index cf00c0a7e55c..b51221b94b0b 100644
> --- a/drivers/vfio/pci/Makefile
> +++ b/drivers/vfio/pci/Makefile
> @@ -8,6 +8,9 @@ vfio-pci-y := vfio_pci.o
>  vfio-pci-$(CONFIG_VFIO_PCI_IGD) += vfio_pci_igd.o
>  obj-$(CONFIG_VFIO_PCI) += vfio-pci.o
>  
> +vfio-cxl-core-y := vfio_cxl_core.o
> +obj-$(CONFIG_VFIO_CXL_CORE) += vfio-cxl-core.o
> +
>  obj-$(CONFIG_MLX5_VFIO_PCI)           += mlx5/
>  
>  obj-$(CONFIG_HISI_ACC_VFIO_PCI) += hisilicon/
> diff --git a/drivers/vfio/pci/vfio_cxl_core.c b/drivers/vfio/pci/vfio_cxl_core.c
> new file mode 100644
> index 000000000000..6a7859333f67
> --- /dev/null
> +++ b/drivers/vfio/pci/vfio_cxl_core.c
> @@ -0,0 +1,264 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2024, NVIDIA CORPORATION & AFFILIATES. All rights reserved
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/device.h>
> +#include <linux/eventfd.h>
> +#include <linux/file.h>
> +#include <linux/interrupt.h>
> +#include <linux/iommu.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/notifier.h>
> +#include <linux/pci.h>
> +#include <linux/pm_runtime.h>
> +#include <linux/slab.h>
> +#include <linux/types.h>
> +#include <linux/uaccess.h>
> +
> +#include "vfio_pci_priv.h"
> +
> +#define DRIVER_AUTHOR "Zhi Wang <zhiw@nvidia.com>"
> +#define DRIVER_DESC "core driver for VFIO based CXL devices"
> +
> +static int get_hpa_and_request_dpa(struct vfio_pci_core_device *core_dev)
> +{
> +	struct vfio_cxl *cxl = &core_dev->cxl;
> +	struct pci_dev *pdev = core_dev->pdev;
> +	u64 max;
> +
> +	cxl->cxlrd = cxl_get_hpa_freespace(cxl->endpoint, 1,
> +					   CXL_DECODER_F_RAM |
> +					   CXL_DECODER_F_TYPE2,
> +					   &max);

I don't see that this adhere to the comment in cxl_get_hpa_freespace()
that the caller needs to deal with the elevated ref count on the root
decoder.  There's no put_device() call in either the error path or
disable path.

Also, maybe this is inherent in the cxl code, but cxl->cxlrd seems
redundant to me, couldn't we refer to this as cxl->root_decoder? (or
some variant more descriptive than "rd")

Is this exclusively a type2 extension or how do you envision type1/3
devices with vfio?

> +	if (IS_ERR(cxl->cxlrd)) {
> +		pci_err(pdev, "Fail to get HPA space.\n");
> +		return PTR_ERR(cxl->cxlrd);
> +	}
> +
> +	if (max < cxl->region.size) {
> +		pci_err(pdev, "No enough free HPA space %llu < %llu\n",
> +			max, cxl->region.size);
> +		return -ENOSPC;
> +	}
> +
> +	cxl->cxled = cxl_request_dpa(cxl->endpoint, true, cxl->region.size,
> +				     cxl->region.size);

cxl->endpoint_decoder? cxl->endp_dec?

> +	if (IS_ERR(cxl->cxled)) {
> +		pci_err(pdev, "Fail to request DPA\n");
> +		return PTR_ERR(cxl->cxled);
> +	}
> +
> +	return 0;
> +}
> +
> +static int create_cxl_region(struct vfio_pci_core_device *core_dev)
> +{
> +	struct vfio_cxl *cxl = &core_dev->cxl;
> +	struct pci_dev *pdev = core_dev->pdev;
> +	resource_size_t start, end;
> +	int ret;
> +
> +	ret = cxl_accel_request_resource(cxl->cxlds, true);
> +	if (ret) {
> +		pci_err(pdev, "Fail to request CXL resource\n");
> +		return ret;
> +	}

Where is the corresponding release_resource()?

> +
> +	if (!cxl_await_media_ready(cxl->cxlds)) {
> +		cxl_accel_set_media_ready(cxl->cxlds);
> +	} else {
> +		pci_err(pdev, "CXL media is not active\n");
> +		return ret;
> +	}

We're not capturing the media ready error for this return.  I think
Jason would typically suggest a success oriented flow as:

	ret = cxl_await_media_ready(cxl->cxlds)
	if (ret) {
		pci_err(...);
		return ret;
	}
	cxl_accel_set_media_ready(cxl->cxlds);

> +
> +	cxl->cxlmd = devm_cxl_add_memdev(&pdev->dev, cxl->cxlds);
> +	if (IS_ERR(cxl->cxlmd)) {
> +		pci_err(pdev, "Fail to create CXL memdev\n");
> +		return PTR_ERR(cxl->cxlmd);
> +	}
> +
> +	cxl->endpoint = cxl_acquire_endpoint(cxl->cxlmd);
> +	if (IS_ERR(cxl->endpoint)) {
> +		pci_err(pdev, "Fail to acquire CXL endpoint\n");
> +		return PTR_ERR(cxl->endpoint);
> +	}
> +
> +	ret = get_hpa_and_request_dpa(core_dev);
> +	if (ret)
> +		goto out;
> +
> +	cxl->region.region = cxl_create_region(cxl->cxlrd, &cxl->cxled, 1);
> +	if (IS_ERR(cxl->region.region)) {
> +		ret = PTR_ERR(cxl->region.region);
> +		pci_err(pdev, "Fail to create CXL region\n");
> +		cxl_dpa_free(cxl->cxled);
> +		goto out;
> +	}
> +
> +	cxl_accel_get_region_params(cxl->region.region, &start, &end);
> +
> +	cxl->region.addr = start;
> +out:
> +	cxl_release_endpoint(cxl->cxlmd, cxl->endpoint);
> +	return ret;
> +}
> +
> +/* Standard CXL-type 2 driver initialization sequence */
> +static int enable_cxl(struct vfio_pci_core_device *core_dev, u16 dvsec)
> +{
> +	struct vfio_cxl *cxl = &core_dev->cxl;
> +	struct pci_dev *pdev = core_dev->pdev;
> +	u32 count;
> +	u64 offset, size;
> +	int ret;
> +
> +	cxl->cxlds = cxl_accel_state_create(&pdev->dev, cxl->caps);
> +	if (IS_ERR(cxl->cxlds))
> +		return PTR_ERR(cxl->cxlds);
> +
> +	cxl_accel_set_dvsec(cxl->cxlds, dvsec);
> +	cxl_accel_set_serial(cxl->cxlds, pdev->dev.id);

Doesn't seem to meet the description were cxl_device_state.serial is
described as the PCIe device serial number, not a struct device
instance number.

> +
> +	cxl_accel_set_resource(cxl->cxlds, cxl->dpa_res, CXL_ACCEL_RES_DPA);
> +	cxl_accel_set_resource(cxl->cxlds, cxl->ram_res, CXL_ACCEL_RES_RAM);
> +
> +	ret = cxl_pci_accel_setup_regs(pdev, cxl->cxlds);
> +	if (ret) {
> +		pci_err(pdev, "Fail to setup CXL accel regs\n");
> +		return ret;
> +	}
> +
> +	ret = cxl_get_hdm_info(cxl->cxlds, &count, &offset, &size);
> +	if (ret)
> +		return ret;
> +
> +	if (!count || !size) {
> +		pci_err(pdev, "Fail to find CXL HDM reg offset\n");
> +		return -ENODEV;
> +	}
> +
> +	cxl->hdm_count = count;
> +	cxl->hdm_reg_offset = offset;
> +	cxl->hdm_reg_size = size;
> +
> +	return create_cxl_region(core_dev);
> +}
> +
> +static void disable_cxl(struct vfio_pci_core_device *core_dev)
> +{
> +	struct vfio_cxl *cxl = &core_dev->cxl;
> +
> +	if (cxl->region.region)
> +		cxl_region_detach(cxl->cxled);
> +
> +	if (cxl->cxled)
> +		cxl_dpa_free(cxl->cxled);
> +}
> +
> +int vfio_cxl_core_enable(struct vfio_pci_core_device *core_dev)
> +{
> +	struct vfio_cxl *cxl = &core_dev->cxl;
> +	struct pci_dev *pdev = core_dev->pdev;
> +	u16 dvsec;
> +	int ret;
> +
> +	dvsec = pci_find_dvsec_capability(pdev, PCI_VENDOR_ID_CXL,
> +					  CXL_DVSEC_PCIE_DEVICE);
> +	if (!dvsec)
> +		return -ENODEV;
> +
> +	if (!cxl->region.size)
> +		return -EINVAL;
> +
> +	ret = vfio_pci_core_enable(core_dev);
> +	if (ret)
> +		return ret;
> +
> +	ret = enable_cxl(core_dev, dvsec);
> +	if (ret)
> +		goto err_enable_cxl_device;
> +
> +	return 0;
> +
> +err_enable_cxl_device:
> +	vfio_pci_core_disable(core_dev);
> +	return ret;
> +}
> +EXPORT_SYMBOL(vfio_cxl_core_enable);

These should all be _GPL symbols by default, right?

> +
> +void vfio_cxl_core_finish_enable(struct vfio_pci_core_device *core_dev)
> +{
> +	vfio_pci_core_finish_enable(core_dev);
> +}
> +EXPORT_SYMBOL(vfio_cxl_core_finish_enable);
> +
> +void vfio_cxl_core_close_device(struct vfio_device *vdev)
> +{
> +	struct vfio_pci_core_device *core_dev =
> +		container_of(vdev, struct vfio_pci_core_device, vdev);
> +
> +	disable_cxl(core_dev);
> +	vfio_pci_core_close_device(vdev);
> +}
> +EXPORT_SYMBOL(vfio_cxl_core_close_device);
> +
> +/*
> + * Configure the resource required by the kernel CXL core:
> + * device DPA and device RAM size
> + */
> +void vfio_cxl_core_set_resource(struct vfio_pci_core_device *core_dev,
> +				struct resource res,
> +				enum accel_resource type)
> +{
> +	struct vfio_cxl *cxl = &core_dev->cxl;
> +
> +	switch (type) {
> +	case CXL_ACCEL_RES_DPA:
> +		cxl->dpa_size = res.end - res.start + 1;
> +		cxl->dpa_res = res;
> +		break;
> +
> +	case CXL_ACCEL_RES_RAM:
> +		cxl->ram_res = res;
> +		break;
> +
> +	default:
> +		WARN(1, "invalid resource type: %d\n", type);
> +		break;
> +	}
> +}
> +EXPORT_SYMBOL(vfio_cxl_core_set_resource);

It's not obvious to me why we want to multiplex these through one
function rather than have separate functions to set the dpa and ram.
The usage in patch 12/ doesn't really dictate a multiplexed function.

> +
> +/* Configure the expected CXL region size to be created */
> +void vfio_cxl_core_set_region_size(struct vfio_pci_core_device *core_dev,
> +				   u64 size)
> +{
> +	struct vfio_cxl *cxl = &core_dev->cxl;
> +
> +	if (WARN_ON(size > cxl->dpa_size))
> +		return;
> +
> +	if (WARN_ON(cxl->region.region))
> +		return;
> +
> +	cxl->region.size = size;
> +}
> +EXPORT_SYMBOL(vfio_cxl_core_set_region_size);
> +
> +/* Configure the driver cap required by the kernel CXL core */
> +void vfio_cxl_core_set_driver_hdm_cap(struct vfio_pci_core_device *core_dev)
> +{
> +	struct vfio_cxl *cxl = &core_dev->cxl;
> +
> +	cxl->caps |= CXL_ACCEL_DRIVER_CAP_HDM;
> +}
> +EXPORT_SYMBOL(vfio_cxl_core_set_driver_hdm_cap);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR(DRIVER_AUTHOR);
> +MODULE_DESCRIPTION(DRIVER_DESC);
> +MODULE_IMPORT_NS(CXL);
> diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
> index fbb472dd99b3..7762d4a3e825 100644
> --- a/include/linux/vfio_pci_core.h
> +++ b/include/linux/vfio_pci_core.h
> @@ -15,6 +15,8 @@
>  #include <linux/types.h>
>  #include <linux/uuid.h>
>  #include <linux/notifier.h>
> +#include <linux/cxl_accel_mem.h>
> +#include <linux/cxl_accel_pci.h>
>  
>  #ifndef VFIO_PCI_CORE_H
>  #define VFIO_PCI_CORE_H
> @@ -49,6 +51,31 @@ struct vfio_pci_region {
>  	u32				flags;
>  };
>  
> +struct vfio_cxl_region {
> +	u64 size;
> +	u64 addr;
> +	struct cxl_region *region;
> +};
> +
> +struct vfio_cxl {
> +	u8 caps;
> +	u64 dpa_size;
> +
> +	u32 hdm_count;

Poor packing, caps and hdm_count should at least be adjacent to leave
only a single 24-bit gap.

> +	u64 hdm_reg_offset;
> +	u64 hdm_reg_size;
> +
> +	struct cxl_dev_state *cxlds;
> +	struct cxl_memdev *cxlmd;
> +	struct cxl_root_decoder *cxlrd;
> +	struct cxl_port *endpoint;
> +	struct cxl_endpoint_decoder *cxled;
> +	struct resource dpa_res;
> +	struct resource ram_res;
> +
> +	struct vfio_cxl_region region;
> +};
> +
>  struct vfio_pci_core_device {
>  	struct vfio_device	vdev;
>  	struct pci_dev		*pdev;
> @@ -94,6 +121,7 @@ struct vfio_pci_core_device {
>  	struct vfio_pci_core_device	*sriov_pf_core_dev;
>  	struct notifier_block	nb;
>  	struct rw_semaphore	memory_lock;
> +	struct vfio_cxl		cxl;

I'd prefer we not embed a structure here that's unused for 100% of
current use cases.  Why can't we have:

struct vfio_cxl_core_device {
	struct vfio_pci_core_device	pci_core;
	struct vfio_cxl			clx;
};

Thanks,
Alex

>  };
>  
>  /* Will be exported for vfio pci drivers usage */
> @@ -159,4 +187,13 @@ VFIO_IOREAD_DECLARATION(32)
>  VFIO_IOREAD_DECLARATION(64)
>  #endif
>  
> +int vfio_cxl_core_enable(struct vfio_pci_core_device *core_dev);
> +void vfio_cxl_core_finish_enable(struct vfio_pci_core_device *core_dev);
> +void vfio_cxl_core_close_device(struct vfio_device *vdev);
> +void vfio_cxl_core_set_resource(struct vfio_pci_core_device *core_dev,
> +				struct resource res,
> +				enum accel_resource type);
> +void vfio_cxl_core_set_region_size(struct vfio_pci_core_device *core_dev,
> +				   u64 size);
> +void vfio_cxl_core_set_driver_hdm_cap(struct vfio_pci_core_device *core_dev);
>  #endif /* VFIO_PCI_CORE_H */