[PATCH v17 09/18] drm/shmem-helper: Switch drm_gem_shmem_vmap/vunmap to use pin/unpin

From: Dmitry Osipenko
Date: Thu Sep 14 2023 - 19:29:30 EST


The vmapped pages shall be pinned in memory and previously get/put_pages()
were implicitly hard-pinning/unpinning the pages. This will no longer be
the case with addition of memory shrinker because pages_use_count > 0 won't
determine anymore whether pages are hard-pinned (they will be soft-pinned),
while the new pages_pin_count will do the hard-pinning. Switch the
vmap/vunmap() to use pin/unpin() functions in a preparation of addition
of the memory shrinker support to drm-shmem.

Reviewed-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
---
drivers/gpu/drm/drm_gem_shmem_helper.c | 19 ++++++++++++-------
include/drm/drm_gem_shmem_helper.h | 2 +-
2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index a5964f347dda..e33810450324 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -255,6 +255,14 @@ static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem)
return ret;
}

+static void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem)
+{
+ dma_resv_assert_held(shmem->base.resv);
+
+ if (refcount_dec_and_test(&shmem->pages_pin_count))
+ drm_gem_shmem_put_pages_locked(shmem);
+}
+
/**
* drm_gem_shmem_pin - Pin backing pages for a shmem GEM object
* @shmem: shmem GEM object
@@ -302,10 +310,7 @@ void drm_gem_shmem_unpin(struct drm_gem_shmem_object *shmem)
return;

dma_resv_lock(shmem->base.resv, NULL);
-
- if (refcount_dec_and_test(&shmem->pages_pin_count))
- drm_gem_shmem_put_pages_locked(shmem);
-
+ drm_gem_shmem_unpin_locked(shmem);
dma_resv_unlock(shmem->base.resv);
}
EXPORT_SYMBOL_GPL(drm_gem_shmem_unpin);
@@ -343,7 +348,7 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
return 0;
}

- ret = drm_gem_shmem_get_pages_locked(shmem);
+ ret = drm_gem_shmem_pin_locked(shmem);
if (ret)
goto err_zero_use;

@@ -366,7 +371,7 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,

err_put_pages:
if (!obj->import_attach)
- drm_gem_shmem_put_pages_locked(shmem);
+ drm_gem_shmem_unpin_locked(shmem);
err_zero_use:
shmem->vmap_use_count = 0;

@@ -403,7 +408,7 @@ void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem,
return;

vunmap(shmem->vaddr);
- drm_gem_shmem_put_pages_locked(shmem);
+ drm_gem_shmem_unpin_locked(shmem);
}

shmem->vaddr = NULL;
diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
index 3947f5c6bff7..5b1ce7f7a39c 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -123,7 +123,7 @@ int drm_gem_shmem_madvise_locked(struct drm_gem_shmem_object *shmem, int madv);
static inline bool drm_gem_shmem_is_purgeable(struct drm_gem_shmem_object *shmem)
{
return (shmem->madv > 0) &&
- !shmem->vmap_use_count && shmem->sgt &&
+ !refcount_read(&shmem->pages_pin_count) && shmem->sgt &&
!shmem->base.dma_buf && !shmem->base.import_attach;
}

--
2.41.0