[PATCH v3] drm/xe: Support for mmap-ing mmio regions
Upadhyay, Tejas
tejas.upadhyay at intel.com
Wed Jul 2 13:25:17 UTC 2025
> -----Original Message-----
> From: Levi, Ilia <ilia.levi at intel.com>
> Sent: 24 June 2025 21:22
> To: intel-xe at lists.freedesktop.org
> Cc: Levi, Ilia <ilia.levi at intel.com>; Elbaz, Koby <koby.elbaz at intel.com>; Sinyuk,
> Konstantin <konstantin.sinyuk at intel.com>; Avizrat, Yaron
> <yaron.avizrat at intel.com>; Haimovski, Moti <moti.haimovski at intel.com>;
> Freiman, Didi <didi.freiman at intel.com>; Upadhyay, Tejas
> <tejas.upadhyay at intel.com>; Auld, Matthew <matthew.auld at intel.com>;
> Roper, Matthew D <matthew.d.roper at intel.com>; Brost, Matthew
> <matthew.brost at intel.com>
> Subject: [PATCH v3] drm/xe: Support for mmap-ing mmio regions
>
> Allow the driver to expose hardware register spaces to userspace through
> GEM objects with fake mmap offsets. This can be useful for userspace-
> firmware communication, debugging, etc.
>
> v2: Minor doc fix (CI)
> v3: Enforce MAP_SHARED (Tejas)
> Add fault handler with dummy page (Tejas, Matt Auld)
> Store physical address instead of xe_mmio in the GEM object (MattB)
>
> Signed-off-by: Ilia Levi <ilia.levi at intel.com>
> ---
> drivers/gpu/drm/xe/xe_device_types.h | 14 ++
> drivers/gpu/drm/xe/xe_mmio.c | 210
> +++++++++++++++++++++++++++
> drivers/gpu/drm/xe/xe_mmio.h | 4 +
> 3 files changed, 228 insertions(+)
>
> diff --git a/drivers/gpu/drm/xe/xe_device_types.h
> b/drivers/gpu/drm/xe/xe_device_types.h
> index 6aca4b1a2824..22a567c5f0de 100644
> --- a/drivers/gpu/drm/xe/xe_device_types.h
> +++ b/drivers/gpu/drm/xe/xe_device_types.h
> @@ -10,6 +10,7 @@
>
> #include <drm/drm_device.h>
> #include <drm/drm_file.h>
> +#include <drm/drm_gem.h>
> #include <drm/drm_pagemap.h>
> #include <drm/ttm/ttm_device.h>
>
> @@ -162,6 +163,19 @@ struct xe_mmio {
> u32 adj_offset;
> };
>
> +/**
> + * struct xe_mmio_gem - GEM wrapper for xe_mmio
> + *
> + * A GEM object for exposing xe_mmio instance to userspace via mmap.
> + */
> +struct xe_mmio_gem {
> + /** @base: GEM object base */
> + struct drm_gem_object base;
> +
> + /** @phys_addr: The physical address of the exposed MMIO region */
> + phys_addr_t phys_addr;
> +};
> +
> /**
> * struct xe_tile - hardware tile structure
> *
> diff --git a/drivers/gpu/drm/xe/xe_mmio.c b/drivers/gpu/drm/xe/xe_mmio.c
> index 7357458bc0d2..3298ab0f1fb4 100644
> --- a/drivers/gpu/drm/xe/xe_mmio.c
> +++ b/drivers/gpu/drm/xe/xe_mmio.c
> @@ -10,6 +10,7 @@
> #include <linux/minmax.h>
> #include <linux/pci.h>
>
> +#include <drm/drm_drv.h>
> #include <drm/drm_managed.h>
> #include <drm/drm_print.h>
>
> @@ -408,3 +409,212 @@ int xe_mmio_wait32_not(struct xe_mmio *mmio,
> struct xe_reg reg, u32 mask, u32 va {
> return __xe_mmio_wait32(mmio, reg, mask, val, timeout_us, out_val,
> atomic, false); }
> +
> +/**
> + * 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. Define an xe_mmio instance that represents this portion.
> + * 2. Call xe_mmio_gem_create() to create a GEM object with an mmap-able
> fake offset.
> + * 3. Use drm_vma_node_offset_addr() on the created GEM object to
> retrieve the fake offset.
> + * 4. Provide the fake offset to userspace.
> + * 5. Userspace can call mmap with the fake offset. The length provided to
> mmap
> + * must match the size of the xe_mmio instance.
> + * 6. When the region is no longer needed, call xe_mmio_gem_destroy() to
> release the GEM object.
> + *
> + * Limitations: The exposed xe_mmio 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 *);
> +
> +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); }
> +
> +static inline phys_addr_t xe_mmio_phys_addr(struct xe_mmio *mmio) {
> + struct xe_device *xe = tile_to_xe(mmio->tile);
> +
> + /*
> + * All MMIO instances are currently on PCI BAR 0, so we can do the
> trick below.
> + * In the future we may want to store the physical address in struct
> xe_mmio.
> + */
> + return pci_resource_start(to_pci_dev(xe->drm.dev),
> GTTMMADR_BAR) +
> + (uintptr_t)(mmio->regs - xe->mmio.regs); }
Can you please elaborate which physical addresses mapped here!
> +
> +/**
> + * xe_mmio_gem_create - Expose an MMIO region to userspace
> + * @mmio: xe_mmio instance
> + * @file: DRM file descriptor
> + *
> + * This function creates a GEM object with an mmap-able fake offset
> +that wraps
> + * the provided xe_mmio instance.
> + *
> + * See: "Exposing MMIO regions to userspace"
> + */
> +struct xe_mmio_gem *
> +xe_mmio_gem_create(struct xe_mmio *mmio, struct drm_file *file) {
> + struct xe_device *xe = tile_to_xe(mmio->tile);
> + size_t size = mmio->regs_size;
> + struct xe_mmio_gem *obj;
> + struct drm_gem_object *base;
> + phys_addr_t phys_addr = xe_mmio_phys_addr(mmio);
> + 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);
> +}
> +
> +static void xe_mmio_gem_free(struct drm_gem_object *base) {
> + struct xe_mmio_gem *obj = to_xe_mmio_gem(base);
> +
We can release fake offset here!
Tejas
> + drm_gem_object_release(base);
> + kfree(obj);
> +}
> +
> +/**
> + * xe_mmio_gem_destroy - Destroy the GEM object wrapping xe_mmio
> + * @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;
> +}
> diff --git a/drivers/gpu/drm/xe/xe_mmio.h b/drivers/gpu/drm/xe/xe_mmio.h
> index c151ba569003..2990bbcef24d 100644
> --- a/drivers/gpu/drm/xe/xe_mmio.h
> +++ b/drivers/gpu/drm/xe/xe_mmio.h
> @@ -8,6 +8,7 @@
>
> #include "xe_gt_types.h"
>
> +struct drm_file;
> struct xe_device;
> struct xe_reg;
>
> @@ -42,4 +43,7 @@ static inline struct xe_mmio *xe_root_tile_mmio(struct
> xe_device *xe)
> return &xe->tiles[0].mmio;
> }
>
> +struct xe_mmio_gem *xe_mmio_gem_create(struct xe_mmio *mmio, struct
> +drm_file *file); void xe_mmio_gem_destroy(struct xe_mmio_gem *gem);
> +
> #endif
> --
> 2.43.0
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