On Tue, 2025-10-28 at 19:17 -0700, Matthew Brost wrote:
> On Sat, Oct 25, 2025 at 02:04:10PM +0200, Thomas Hellström wrote:
> > Mimic the dma-buf method using dma_[map|unmap]_resource to map
> > for pcie-p2p dma.
> >
> > There's an ongoing area of work upstream to sort out how this best
> > should be done. One method proposed is to add an additional
> > pci_p2p_dma_pagemap aliasing the device_private pagemap and use
> > the corresponding pci_p2p_dma_pagemap page as input for
> > dma_map_page(). However, that would incur double the amount of
> > memory and latency to set up the drm_pagemap and given the huge
> > amount of memory present on modern GPUs, that would really not
> > work.
> > Hence the simple approach used in this patch.
> >
> > Signed-off-by: Thomas Hellström <[email protected]>
> > ---
> > drivers/gpu/drm/xe/xe_svm.c | 44
> > ++++++++++++++++++++++++++++++++++---
> > drivers/gpu/drm/xe/xe_svm.h | 1 +
> > 2 files changed, 42 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/xe/xe_svm.c
> > b/drivers/gpu/drm/xe/xe_svm.c
> > index 9dd96dad2cca..9814f95cb212 100644
> > --- a/drivers/gpu/drm/xe/xe_svm.c
> > +++ b/drivers/gpu/drm/xe/xe_svm.c
> > @@ -3,6 +3,8 @@
> > * Copyright © 2024 Intel Corporation
> > */
> >
> > +#include <linux/pci-p2pdma.h>
> > +
> > #include <drm/drm_drv.h>
> > #include <drm/drm_managed.h>
> > #include <drm/drm_pagemap.h>
> > @@ -442,6 +444,24 @@ static u64 xe_page_to_dpa(struct page *page)
> > return dpa;
> > }
> >
> > +static u64 xe_page_to_pcie(struct page *page)
> > +{
>
> This function looks almost exactly the same as xe_page_to_dpa, maybe
> extract out the common parts?
OK, I'll take a look at that.
/Thomas
>
> Everything else LGTM.
>
> Matt
>
> > + struct xe_pagemap *xpagemap = xe_page_to_pagemap(page);
> > + struct xe_vram_region *vr = xe_pagemap_to_vr(xpagemap);
> > + u64 hpa_base = xpagemap->hpa_base;
> > + u64 ioaddr;
> > + u64 pfn = page_to_pfn(page);
> > + u64 offset;
> > +
> > + xe_assert(vr->xe, is_device_private_page(page));
> > + xe_assert(vr->xe, (pfn << PAGE_SHIFT) >= hpa_base);
> > +
> > + offset = (pfn << PAGE_SHIFT) - hpa_base;
> > + ioaddr = vr->io_start + offset;
> > +
> > + return ioaddr;
> > +}
> > +
> > enum xe_svm_copy_dir {
> > XE_SVM_COPY_TO_VRAM,
> > XE_SVM_COPY_TO_SRAM,
> > @@ -793,7 +813,10 @@ static bool xe_has_interconnect(struct
> > drm_pagemap_peer *peer1,
> > struct device *dev1 = xe_peer_to_dev(peer1);
> > struct device *dev2 = xe_peer_to_dev(peer2);
> >
> > - return dev1 == dev2;
> > + if (dev1 == dev2)
> > + return true;
> > +
> > + return pci_p2pdma_distance(to_pci_dev(dev1), dev2, true)
> > >= 0;
> > }
> >
> > static DRM_PAGEMAP_OWNER_LIST_DEFINE(xe_owner_list);
> > @@ -1530,13 +1553,27 @@ xe_drm_pagemap_device_map(struct
> > drm_pagemap *dpagemap,
> > addr = xe_page_to_dpa(page);
> > prot = XE_INTERCONNECT_VRAM;
> > } else {
> > - addr = DMA_MAPPING_ERROR;
> > - prot = 0;
> > + addr = dma_map_resource(dev,
> > + xe_page_to_pcie(page),
> > + PAGE_SIZE << order, dir,
> > + DMA_ATTR_SKIP_CPU_SYNC);
> > + prot = XE_INTERCONNECT_P2P;
> > }
> >
> > return drm_pagemap_addr_encode(addr, prot, order, dir);
> > }
> >
> > +static void xe_drm_pagemap_device_unmap(struct drm_pagemap
> > *dpagemap,
> > + struct device *dev,
> > + struct drm_pagemap_addr
> > addr)
> > +{
> > + if (addr.proto != XE_INTERCONNECT_P2P)
> > + return;
> > +
> > + dma_unmap_resource(dev, addr.addr, PAGE_SIZE <<
> > addr.order,
> > + addr.dir, DMA_ATTR_SKIP_CPU_SYNC);
> > +}
> > +
> > static void xe_pagemap_destroy_work(struct work_struct *work)
> > {
> > struct xe_pagemap *xpagemap = container_of(work,
> > typeof(*xpagemap), destroy_work);
> > @@ -1573,6 +1610,7 @@ static void xe_pagemap_destroy(struct
> > drm_pagemap *dpagemap, bool from_atomic_or
> >
> > static const struct drm_pagemap_ops xe_drm_pagemap_ops = {
> > .device_map = xe_drm_pagemap_device_map,
> > + .device_unmap = xe_drm_pagemap_device_unmap,
> > .populate_mm = xe_drm_pagemap_populate_mm,
> > .destroy = xe_pagemap_destroy,
> > };
> > diff --git a/drivers/gpu/drm/xe/xe_svm.h
> > b/drivers/gpu/drm/xe/xe_svm.h
> > index 7cd7932f56c8..f5ed48993b6d 100644
> > --- a/drivers/gpu/drm/xe/xe_svm.h
> > +++ b/drivers/gpu/drm/xe/xe_svm.h
> > @@ -13,6 +13,7 @@
> > #include <drm/drm_pagemap_util.h>
> >
> > #define XE_INTERCONNECT_VRAM DRM_INTERCONNECT_DRIVER
> > +#define XE_INTERCONNECT_P2P (XE_INTERCONNECT_VRAM + 1)
> >
> > struct drm_device;
> > struct drm_file;
> > --
> > 2.51.0
> >
