[PATCH 5.15 155/207] drm/msm: Fix mmap to include VM_IO and VM_DONTDUMP

Greg Kroah-Hartman
2021-12-06T15:59:55Z

From: Douglas Anderson <dianders@chromium.org>

[ Upstream commit 3466d9e217b337bf473ee629c608e53f9f3ab786 ]

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@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Tested-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/20211110113334.1.I1687e716adb2df746da58b508db3f25423c40b27@changeid
Signed-off-by: Rob Clark <robdclark@chromium.org>
Signed-off-by: Sasha Levin <sashal@kernel.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 bd6ec04f345e1..cb52ac01e5122 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -1055,8 +1055,7 @@ 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;
--
2.33.0