linux-kernel - [PATCH] drm/msm: Fix mmap to include VM_IO and VM

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Date:   Wed, 10 Nov 2021 11:33:42 -0800
From:   Douglas Anderson <dianders@...omium.org>
To:     Rob Clark <robdclark@...il.com>
Cc:     Douglas Anderson <dianders@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>, Sean Paul <sean@...rly.run>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] drm/msm: Fix mmap to include VM_IO and VM_DONTDUMP

In commit 510410bfc034 ("drm/msm: Implement mmap as GEM object
function") we switched to a new/cleaner method of doing things. That's
good, but we missed a little bit.

Before that commit, we used to _first_ run through the
drm_gem_mmap_obj() case where `obj->funcs->mmap()` was NULL. That meant
that we ran:

  vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
  vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
  vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);

...and _then_ we modified those mappings with our own. Now that
`obj->funcs->mmap()` is no longer NULL we don't run the default
code. It looks like the fact that the vm_flags got VM_IO / VM_DONTDUMP
was important because we're now getting crashes on Chromebooks that
use ARC++ while logging out. Specifically a crash that looks like this
(this is on a 5.10 kernel w/ relevant backports but also seen on a
5.15 kernel):

  Unable to handle kernel paging request at virtual address ffffffc008000000
  Mem abort info:
    ESR = 0x96000006
    EC = 0x25: DABT (current EL), IL = 32 bits
    SET = 0, FnV = 0
    EA = 0, S1PTW = 0
  Data abort info:
    ISV = 0, ISS = 0x00000006
    CM = 0, WnR = 0
  swapper pgtable: 4k pages, 39-bit VAs, pgdp=000000008293d000
  [ffffffc008000000] pgd=00000001002b3003, p4d=00000001002b3003,
                     pud=00000001002b3003, pmd=0000000000000000
  Internal error: Oops: 96000006 [#1] PREEMPT SMP
  [...]
  CPU: 7 PID: 15734 Comm: crash_dump64 Tainted: G W 5.10.67 #1 [...]
  Hardware name: Qualcomm Technologies, Inc. sc7280 IDP SKU2 platform (DT)
  pstate: 80400009 (Nzcv daif +PAN -UAO -TCO BTYPE=--)
  pc : __arch_copy_to_user+0xc0/0x30c
  lr : copyout+0xac/0x14c
  [...]
  Call trace:
   __arch_copy_to_user+0xc0/0x30c
   copy_page_to_iter+0x1a0/0x294
   process_vm_rw_core+0x240/0x408
   process_vm_rw+0x110/0x16c
   __arm64_sys_process_vm_readv+0x30/0x3c
   el0_svc_common+0xf8/0x250
   do_el0_svc+0x30/0x80
   el0_svc+0x10/0x1c
   el0_sync_handler+0x78/0x108
   el0_sync+0x184/0x1c0
  Code: f8408423 f80008c3 910020c6 36100082 (b8404423)

Let's add the two flags back in.

While we're at it, the fact that we aren't running the default means
that we _don't_ need to clear out VM_PFNMAP, so remove that and save
an instruction.

NOTE: it was confirmed that VM_IO was the important flag to fix the
problem I was seeing, but adding back VM_DONTDUMP seems like a sane
thing to do so I'm doing that too.

Fixes: 510410bfc034 ("drm/msm: Implement mmap as GEM object function")
Reported-by: Stephen Boyd <swboyd@...omium.org>
Signed-off-by: Douglas Anderson <dianders@...omium.org>
---

 drivers/gpu/drm/msm/msm_gem.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index 6b03e00cc5f2..ae18bfb22502 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -1056,8 +1056,7 @@ static int msm_gem_object_mmap(struct drm_gem_object *obj, struct vm_area_struct
 {
 	struct msm_gem_object *msm_obj = to_msm_bo(obj);
 
-	vma->vm_flags &= ~VM_PFNMAP;
-	vma->vm_flags |= VM_MIXEDMAP | VM_DONTEXPAND;
+	vma->vm_flags |= VM_IO | VM_MIXEDMAP | VM_DONTEXPAND | VM_DONTDUMP;
 	vma->vm_page_prot = msm_gem_pgprot(msm_obj, vm_get_page_prot(vma->vm_flags));
 
 	return 0;
-- 
2.34.0.rc1.387.gb447b232ab-goog