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// SPDX-License-Identifier: MIT
/*
* Copyright © 2025 Intel Corporation
*/
#include "xe_mmio_gem.h"
#include <drm/drm_drv.h>
#include <drm/drm_gem.h>
#include <drm/drm_managed.h>
#include "xe_device_types.h"
/**
* DOC: Exposing MMIO regions to userspace
*
* In certain cases, the driver may allow userspace to mmap a portion of the hardware registers.
*
* This can be done as follows:
* 1. Call xe_mmio_gem_create() to create a GEM object with an mmap-able fake offset.
* 2. Use xe_mmio_gem_mmap_offset() on the created GEM object to retrieve the fake offset.
* 3. Provide the fake offset to userspace.
* 4. Userspace can call mmap with the fake offset. The length provided to mmap
* must match the size of the GEM object.
* 5. When the region is no longer needed, call xe_mmio_gem_destroy() to release the GEM object.
*
* NOTE: The exposed MMIO region must be page-aligned with regards to its BAR offset and size.
*
* WARNING: Exposing MMIO regions to userspace can have security and stability implications.
* Make sure not to expose any sensitive registers.
*/
static void xe_mmio_gem_free(struct drm_gem_object *);
static int xe_mmio_gem_mmap(struct drm_gem_object *, struct vm_area_struct *);
static vm_fault_t xe_mmio_gem_vm_fault(struct vm_fault *);
struct xe_mmio_gem {
struct drm_gem_object base;
phys_addr_t phys_addr;
};
static const struct vm_operations_struct vm_ops = {
.open = drm_gem_vm_open,
.close = drm_gem_vm_close,
.fault = xe_mmio_gem_vm_fault,
};
static const struct drm_gem_object_funcs xe_mmio_gem_funcs = {
.free = xe_mmio_gem_free,
.mmap = xe_mmio_gem_mmap,
.vm_ops = &vm_ops,
};
static inline struct xe_mmio_gem *to_xe_mmio_gem(struct drm_gem_object *obj)
{
return container_of(obj, struct xe_mmio_gem, base);
}
/**
* xe_mmio_gem_create - Expose an MMIO region to userspace
* @xe: The xe device
* @file: DRM file descriptor
* @phys_addr: Start of the exposed MMIO region
* @size: The size of the exposed MMIO region
*
* This function creates a GEM object that exposes an MMIO region with an mmap-able
* fake offset.
*
* See: "Exposing MMIO regions to userspace"
*/
struct xe_mmio_gem *xe_mmio_gem_create(struct xe_device *xe, struct drm_file *file,
phys_addr_t phys_addr, size_t size)
{
struct xe_mmio_gem *obj;
struct drm_gem_object *base;
int err;
if ((phys_addr % PAGE_SIZE != 0) || (size % PAGE_SIZE != 0))
return ERR_PTR(-EINVAL);
obj = kzalloc(sizeof(*obj), GFP_KERNEL);
if (!obj)
return ERR_PTR(-ENOMEM);
base = &obj->base;
base->funcs = &xe_mmio_gem_funcs;
obj->phys_addr = phys_addr;
drm_gem_private_object_init(&xe->drm, base, size);
err = drm_gem_create_mmap_offset(base);
if (err)
goto free_gem;
err = drm_vma_node_allow(&base->vma_node, file);
if (err)
goto free_gem;
return obj;
free_gem:
xe_mmio_gem_free(base);
return ERR_PTR(err);
}
/**
* xe_mmio_gem_mmap_offset - Return the mmap-able fake offset
* @gem: the GEM object created with xe_mmio_gem_create()
*
* This function returns the mmap-able fake offset allocated during
* xe_mmio_gem_create().
*
* See: "Exposing MMIO regions to userspace"
*/
u64 xe_mmio_gem_mmap_offset(struct xe_mmio_gem *gem)
{
return drm_vma_node_offset_addr(&gem->base.vma_node);
}
static void xe_mmio_gem_free(struct drm_gem_object *base)
{
struct xe_mmio_gem *obj = to_xe_mmio_gem(base);
drm_gem_object_release(base);
kfree(obj);
}
/**
* xe_mmio_gem_destroy - Destroy the GEM object that exposes an MMIO region
* @gem: the GEM object to destroy
*
* This function releases resources associated with the GEM object created by
* xe_mmio_gem_create().
*
* See: "Exposing MMIO regions to userspace"
*/
void xe_mmio_gem_destroy(struct xe_mmio_gem *gem)
{
xe_mmio_gem_free(&gem->base);
}
static int xe_mmio_gem_mmap(struct drm_gem_object *base, struct vm_area_struct *vma)
{
if (vma->vm_end - vma->vm_start != base->size)
return -EINVAL;
if ((vma->vm_flags & VM_SHARED) == 0)
return -EINVAL;
/* Set vm_pgoff (used as a fake buffer offset by DRM) to 0 */
vma->vm_pgoff = 0;
vma->vm_page_prot = pgprot_noncached(vm_get_page_prot(vma->vm_flags));
vm_flags_set(vma, VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP |
VM_DONTCOPY | VM_NORESERVE);
/* Defer actual mapping to the fault handler. */
return 0;
}
static void xe_mmio_gem_release_dummy_page(struct drm_device *dev, void *res)
{
__free_page((struct page *)res);
}
static vm_fault_t xe_mmio_gem_vm_fault_dummy_page(struct vm_area_struct *vma)
{
struct drm_gem_object *base = vma->vm_private_data;
struct drm_device *dev = base->dev;
vm_fault_t ret = VM_FAULT_NOPAGE;
struct page *page;
unsigned long pfn;
unsigned long i;
page = alloc_page(GFP_KERNEL | __GFP_ZERO);
if (!page)
return VM_FAULT_OOM;
if (drmm_add_action_or_reset(dev, xe_mmio_gem_release_dummy_page, page))
return VM_FAULT_OOM;
pfn = page_to_pfn(page);
/* Map the entire VMA to the same dummy page */
for (i = 0; i < base->size; i += PAGE_SIZE) {
unsigned long addr = vma->vm_start + i;
ret = vmf_insert_pfn(vma, addr, pfn);
if (ret & VM_FAULT_ERROR)
break;
}
return ret;
}
static vm_fault_t xe_mmio_gem_vm_fault(struct vm_fault *vmf)
{
struct vm_area_struct *vma = vmf->vma;
struct drm_gem_object *base = vma->vm_private_data;
struct xe_mmio_gem *obj = to_xe_mmio_gem(base);
struct drm_device *dev = base->dev;
vm_fault_t ret = VM_FAULT_NOPAGE;
unsigned long i;
int idx;
if (!drm_dev_enter(dev, &idx)) {
/*
* Provide a dummy page to avoid SIGBUS for events such as hot-unplug.
* This gives the userspace the option to recover instead of crashing.
* It is assumed the userspace will receive the notification via some
* other channel (e.g. drm uevent).
*/
return xe_mmio_gem_vm_fault_dummy_page(vma);
}
for (i = 0; i < base->size; i += PAGE_SIZE) {
unsigned long addr = vma->vm_start + i;
unsigned long phys_addr = obj->phys_addr + i;
ret = vmf_insert_pfn(vma, addr, PHYS_PFN(phys_addr));
if (ret & VM_FAULT_ERROR)
break;
}
drm_dev_exit(idx);
return ret;
}
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