linux-kernel - [PATCH 0/2] Fix udmabuf vmap error

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Message-ID: <20250415031548.2007942-1-link@vivo.com>
Date: Tue, 15 Apr 2025 11:15:45 +0800
From: Huan Yang <link@...o.com>
To: Sumit Semwal <sumit.semwal@...aro.org>,
	Christian König <christian.koenig@....com>,
	Gerd Hoffmann <kraxel@...hat.com>,
	Vivek Kasireddy <vivek.kasireddy@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Airlie <airlied@...hat.com>,
	linux-media@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	linaro-mm-sig@...ts.linaro.org,
	linux-kernel@...r.kernel.org
Cc: opensource.kernel@...o.com,
	Huan Yang <link@...o.com>
Subject: [PATCH 0/2] Fix udmabuf vmap error

In [1] Bingbu report an error that vmap_udmabuf invoke failed due to use
vmap_pfn and blocked by !pfn_valid.

Due to misunderstand it, I change vmap_pfn check of !pfn_valid to
pfn_valid, then send [2], then Christoph point that:
  vmap_pfn is entirely for memory not backed by pages or folios,
  i.e. PCIe BARs and similar memory.  This must not be mixed with proper
  folio backed memory.

So, I given a misuse of vmap_pfn. But to fix vmap_udmabuf, and consider
HVO effect, I offer a RFC patchset [3], which simple copy vmap_pfn to
vmap_udmabuf, other implement folio range based vmap.

But in [3], Muchun point that I misunderstand HVO, which do not
released any page struct pointer in vmemmap, only change this VA's PTE
point to hugetlb's **HEAD** page frame, and release remainned **tail** page
frame. So any page struct pointer do exist, and folio_page, folio_pfn or
other api still can work.

By this, we can fix this error simpliy:
 Patch 1 revert this vmap_pfn misuse patch.
 Patch 2 fix missed offset page set.

[1] https://lore.kernel.org/all/9172a601-c360-0d5b-ba1b-33deba430455@linux.intel.com/
[2] https://lore.kernel.org/all/20250312061513.1126496-1-link@vivo.com/
[3] https://lore.kernel.org/all/20250327092922.536-1-link@vivo.com/

Huan Yang (2):
  Revert "udmabuf: fix vmap_udmabuf error page set"
  udmabuf: fix vmap missed offset page

 drivers/dma-buf/Kconfig   |  1 -
 drivers/dma-buf/udmabuf.c | 23 ++++++++---------------
 2 files changed, 8 insertions(+), 16 deletions(-)

base-commit: b425262c07a6a643ebeed91046e161e20b944164
--
2.48.1