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drm/xe: Limit sg segment size to PAGE_SIZE on Xen PV

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Fix display corruption on Xen PV dom0, where DMA buffers are not
guaranteed machine-contiguous, in which case bounce buffering kicks
in, breaking xe's memory coherency assumptions.

Apply the same workaround i915 carries in i915_sg_segment_size() since
commit 78a07fe777 ("drm/i915: stop abusing swiotlb_max_segment").

Fixes: dd08ebf6c3 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/8382
Link: https://lore.kernel.org/xen-devel/aYtznP_tT6xNPwf-@mail-itl/
Link: https://lore.kernel.org/all/20221020110308.1582518-1-hch@lst.de/ # i915 counterpart
Cc: Christoph Hellwig <hch@lst.de>
Cc: Robert Beckett <bob.beckett@collabora.com>
Cc: stable@vger.kernel.org # v6.8+
Signed-off-by: Szymon Acedański <accek@invisiblethingslab.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patch.msgid.link/20260916173030.3223833-1-accek@invisiblethingslab.com
(cherry picked from commit 77f704158f099b952681f207478a22d5b8218edb)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
This commit is contained in:
Szymon Acedański 2026-09-16 19:30:30 +02:00 committed by Rodrigo Vivi
parent 24a22fb3c7
commit 141008dec7
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1 changed files with 19 additions and 0 deletions
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19
drivers/gpu/drm/xe/xe_bo.h
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@ -9,6 +9,8 @@
#include <drm/drm_prime.h>
#include <drm/ttm/ttm_tt.h>
#include <xen/xen.h>
#include "xe_bo_types.h"
#include "xe_ggtt.h"
#include "xe_macros.h"
@ -575,6 +577,23 @@ static inline unsigned int xe_sg_segment_size(struct device *dev)
struct scatterlist __maybe_unused sg;
size_t max = BIT_ULL(sizeof(sg.length) * 8) - 1;
/*
* For Xen PV guests pages aren't contiguous in DMA (machine) address
* space. The DMA API takes care of that both in dma_alloc_* (by
* calling into the hypervisor to make the pages contiguous) and in
* dma_map_* (by bounce buffering). But xe (like i915, see commit
* 78a07fe777c4) ignores the coherency aspects of the DMA API and thus
* can't cope with bounce buffering actually happening, so add a hack
* here to force small allocations and mappings when running in PV
* mode on Xen.
*
* Note this will still break if bounce buffering is required for other
* reasons, like confidential computing hypervisors or PCIe root ports
* with addressing limitations.
*/
if (xen_pv_domain())
return PAGE_SIZE;
max = min_t(size_t, max, dma_max_mapping_size(dev));
/*