Re: [PATCH 1/2] Revert "udmabuf: fix vmap_udmabuf error page set"

[Huan Yang]

在 2025/4/28 12:16, Kasireddy, Vivek 写道:

Hi Huan,

Subject: Re: [PATCH 1/2] Revert "udmabuf: fix vmap_udmabuf error page set"

  From 38aa11d92f209e7529736f3e11e08dfc804bdfae Mon Sep 17 00:00:00
2001
From: Huan Yang <l...@vivo.com>
Date: Tue, 15 Apr 2025 10:04:18 +0800
Subject: [PATCH 1/2] Revert "udmabuf: fix vmap_udmabuf error page set"

This reverts commit 18d7de823b7150344d242c3677e65d68c5271b04.

This given a misuse of vmap_pfn, vmap_pfn give a !pfn_valid check
to avoid user miss use it. This API design to only for none-page struct
based user invoke, i.e. PCIe BARs and other. So any page based will
inject by !pfn_valid check.

udmabuf used shmem or hugetlb as folio src, hence, page/folio based,
can't use it.

Please consider having a commit message like below and resend both patches:
"We cannot use vmap_pfn() in vmap_udmabuf() as it would fail the pfn_valid()
check in vmap_pfn_apply(). This is because vmap_pfn() is intended to be
used for mapping non-struct-page memory such as PCIe BARs. Since, udmabuf
mostly works with pages/folios backed by shmem/hugetlbfs/THP, vmap_pfn()
is not the right tool or API to invoke for implementing vmap."

Thanks, that's clearer, I'll update in v2 version. :)

Huan

Thanks,
Vivek

Signed-off-by: Huan Yang <l...@vivo.com>
Reported-by: Bingbu Cao <bingbu....@linux.intel.com>
Closes: https://lore.kernel.org/dri-devel/eb7e0137-3508-4287-98c4-
816c5fd98...@vivo.com/T/#mbda4f64a3532b32e061f4e8763bc8e307bea3ca
8
Acked-by: Vivek Kasireddy <vivek.kasire...@intel.com>
---
   drivers/dma-buf/Kconfig   |  1 -
   drivers/dma-buf/udmabuf.c | 22 +++++++---------------
   2 files changed, 7 insertions(+), 16 deletions(-)

diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
index fee04fdb0822..b46eb8a552d7 100644
--- a/drivers/dma-buf/Kconfig
+++ b/drivers/dma-buf/Kconfig
@@ -36,7 +36,6 @@ config UDMABUF
       depends on DMA_SHARED_BUFFER
       depends on MEMFD_CREATE || COMPILE_TEST
       depends on MMU
-    select VMAP_PFN
       help
         A driver to let userspace turn memfd regions into dma-bufs.
         Qemu can use this to create host dmabufs for guest framebuffers.
diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index 7eee3eb47a8e..79845565089d 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -109,29 +109,21 @@ static int mmap_udmabuf(struct dma_buf *buf,
struct vm_area_struct *vma)
   static int vmap_udmabuf(struct dma_buf *buf, struct iosys_map *map)
   {
       struct udmabuf *ubuf = buf->priv;
-    unsigned long *pfns;
+    struct page **pages;
       void *vaddr;
       pgoff_t pg;

       dma_resv_assert_held(buf->resv);

-    /**
-     * HVO may free tail pages, so just use pfn to map each folio
-     * into vmalloc area.
-     */
-    pfns = kvmalloc_array(ubuf->pagecount, sizeof(*pfns), GFP_KERNEL);
-    if (!pfns)
+    pages = kvmalloc_array(ubuf->pagecount, sizeof(*pages), GFP_KERNEL);
+    if (!pages)
           return -ENOMEM;

-    for (pg = 0; pg < ubuf->pagecount; pg++) {
-        unsigned long pfn = folio_pfn(ubuf->folios[pg]);
-
-        pfn += ubuf->offsets[pg] >> PAGE_SHIFT;
-        pfns[pg] = pfn;
-    }
+    for (pg = 0; pg < ubuf->pagecount; pg++)
+        pages[pg] = &ubuf->folios[pg]->page;

-    vaddr = vmap_pfn(pfns, ubuf->pagecount, PAGE_KERNEL);
-    kvfree(pfns);
+    vaddr = vm_map_ram(pages, ubuf->pagecount, -1);
+    kvfree(pages);
       if (!vaddr)
           return -EINVAL;

--
2.48.1