[PATCH v3] drm/xe: Support for mmap-ing mmio regions
Levi, Ilia
ilia.levi at intel.com
Tue Jul 8 10:51:33 UTC 2025
On 02/07/2025 16:25, Upadhyay, Tejas wrote:
>
>> -----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!
Could you clarify your comment? xe_mmio_gem_create receives an xe_mmio struct to map.
In order to perform the map, we need to extract from xe_mmio the physical address of the start
of its region and the size of the region. xe_mmio_phys_addr calculates this physical address,
currently by leveraging the fact that xe->mmio.regs points to the start of the BAR. - Ilia
>
>> +
>> +/**
>> + * 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 does that, see:
https://elixir.bootlin.com/linux/v6.15.5/source/drivers/gpu/drm/drm_gem.c#L983
- Ilia
>> + 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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