On 2/9/26 10:27, Thomas Zimmermann wrote:
Invoke folio_mark_accessed() in mmap page faults to add the folio to
the memory manager's LRU list. Userspace invokes mmap to get the memory
for software rendering. Compositors do the same when creating the final
on-screen image, so keeping the pages in LRU makes sense. Avoids paging
out graphics buffers when under memory pressure.
In pfn_mkwrite, further invoke the folio_mark_dirty() to add the folio
for writeback should the underlying file be paged out from system memory.
This rarely happens in practice, yet it would corrupt the buffer content.
This has little effect on a system's hardware-accelerated rendering, which
only mmaps for an initial setup of textures, meshes, shaders, etc.
v3:
- rewrite for VM_PFNMAP
v2:
- adapt to changes in drm_gem_shmem_try_mmap_pmd()
Signed-off-by: Thomas Zimmermann <[email protected]>
Reviewed-by: Boris Brezillon <[email protected]>
Hi Thomas,
I have and Radxa ROCK 5B+ with Mali-G610 GPU and I'm developing the VDRM
(native context) driver
for panthor.ko.
Recently I update my kernel from 7.0 to the 7.1-rc3, and qemu started
freezing with KVM error below
when running any graphical application with Venus or Panthor VDRM. For
some reason Virgl is not affected.
```
error: kvm run failed Bad address
PC=0000ffffb4a86d70 X00=0000ffffb4be5000 X01=0000ffffb2279bb0
X02=0000000000000600 X03=0000ffffb4be5000 X04=0000ffffb227a1b0
X05=0000ffffb4be5600 X06=0000000000000001 X07=0000aaaaf384fd80
X08=dcc58d0daf897753 X09=0000000000000002 X10=0000ffffb4b96758
X11=000000002533f84b X12=0000000000001060 X13=0000000000000000
X14=0000000000000000 X15=0000000000000010 X16=0000ffffb3880128
X17=0000ffffb4a86c80 X18=0000000000000000 X19=0000aaaaf384f8a0
X20=0000aaaaf37cec80 X21=0000aaaaf37c7210 X22=0000aaaaf37c9550
X23=0000aaaaf37c74e0 X24=0000ffffb3b47fc8 X25=0000ffffb3b47fc8
X26=0000ffffb3b43c78 X27=0000aaaaf37e1840 X28=0000aaaaf37cee50
X29=0000ffffecbf1a60 X30=0000ffffb364b530 SP=0000ffffecbf1a60
PSTATE=0000000020001000 --C- EL0t
```
After bisecting I reach to your commit.
```
28e3918179aa75cfd4490b3b0281496ed91d829a drm/gem-shmem:
Track folio accessed/dirty status in mmap
```
It still reproducible in the 7.1-rc4 (ab5fce87a778).
Appling the following patch (Boris suggestion) fixes the issue for me.
```
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c
b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 545933c7f712..1e036f69c1ce 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -696,7 +696,7 @@ const struct vm_operations_struct
drm_gem_shmem_vm_ops = {
#endif
.open = drm_gem_shmem_vm_open,
.close = drm_gem_shmem_vm_close,
- .pfn_mkwrite = drm_gem_shmem_pfn_mkwrite,
+// .pfn_mkwrite = drm_gem_shmem_pfn_mkwrite,
};
EXPORT_SYMBOL_GPL(drm_gem_shmem_vm_ops);
```
I'm not familiar with the drm_gem, code so I don't any more insightful
information
to share. But hopefully we can find a better fix for this.
BR,
Igor Torrente
---
drivers/gpu/drm/drm_gem_shmem_helper.c | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c
b/drivers/gpu/drm/drm_gem_shmem_helper.c
index c3a054899ba3..0c86ad40a049 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -598,6 +598,9 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
if (ret != VM_FAULT_NOPAGE)
ret = vmf_insert_pfn(vma, vmf->address, pfn);
+ if (likely(!(ret & VM_FAULT_ERROR)))
+ folio_mark_accessed(folio);
+
out:
dma_resv_unlock(obj->resv);
@@ -638,10 +641,27 @@ static void drm_gem_shmem_vm_close(struct vm_area_struct *vma)
drm_gem_vm_close(vma);
}
+static vm_fault_t drm_gem_shmem_pfn_mkwrite(struct vm_fault *vmf)
+{
+ struct vm_area_struct *vma = vmf->vma;
+ struct drm_gem_object *obj = vma->vm_private_data;
+ struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+ pgoff_t page_offset = vmf->pgoff - vma->vm_pgoff; /* page offset within
VMA */
+ struct page *page = shmem->pages[page_offset];
+ struct folio *folio = page_folio(page);
+
+ file_update_time(vma->vm_file);
+
+ folio_mark_dirty(folio);
+
+ return 0;
+}
+
const struct vm_operations_struct drm_gem_shmem_vm_ops = {
.fault = drm_gem_shmem_fault,
.open = drm_gem_shmem_vm_open,
.close = drm_gem_shmem_vm_close,
+ .pfn_mkwrite = drm_gem_shmem_pfn_mkwrite,
};
EXPORT_SYMBOL_GPL(drm_gem_shmem_vm_ops);
