[PATCH 3/5] drm/panfrost: Add a no execute flag for BO allocations

[Rob Herring <robh@kernel.org>]

Executable buffers have an alignment restriction that they can't cross
16MB boundary as the GPU program counter is 24-bits. This restriction is
currently not handled and we just get lucky. As current userspace
assumes all BOs are executable, that has to remain the default. So add a
new PANFROST_BO_NOEXEC flag to allow userspace to indicate which BOs are
not executable.

There is also a restriction that executable buffers cannot start or end
on a 4GB boundary. This is mostly avoided as there is only 4GB of space
currently and the beginning is already blocked out for NULL ptr
detection. Add support to handle this restriction fully regardless of
the current constraints.

For existing userspace, all created BOs remain executable, but the GPU
VA alignment will be increased to the size of the BO. This shouldn't
matter as there is plenty of GPU VA space.

Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Cc: Boris Brezillon <boris.brezillon@collabora.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Steven Price <steven.price@arm.com>
Cc: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Signed-off-by: Rob Herring <robh@kernel.org>
---
 drivers/gpu/drm/panfrost/panfrost_drv.c | 20 +++++++++++++++++++-
 drivers/gpu/drm/panfrost/panfrost_gem.c | 18 ++++++++++++++++--
 drivers/gpu/drm/panfrost/panfrost_gem.h |  3 ++-
 drivers/gpu/drm/panfrost/panfrost_mmu.c |  3 +++
 include/uapi/drm/panfrost_drm.h         |  2 ++
 5 files changed, 42 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
index d354b92964d5..b91e991bc6a3 100644
--- a/drivers/gpu/drm/panfrost/panfrost_drv.c
+++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
@@ -49,7 +49,8 @@ static int panfrost_ioctl_create_bo(struct drm_device *dev, void *data,
 	struct panfrost_gem_object *bo;
 	struct drm_panfrost_create_bo *args = data;
 
-	if (!args->size || args->flags || args->pad)
+	if (!args->size || args->pad ||
+	    (args->flags & ~PANFROST_BO_NOEXEC))
 		return -EINVAL;
 
 	bo = panfrost_gem_create_with_handle(file, dev, args->size, args->flags,
@@ -367,6 +368,22 @@ static struct drm_driver panfrost_drm_driver = {
 	.gem_prime_mmap		= drm_gem_prime_mmap,
 };
 
+#define PFN_4G_MASK    ((SZ_4G - 1) >> PAGE_SHIFT)
+
+static void panfrost_drm_mm_color_adjust(const struct drm_mm_node *node,
+					 unsigned long color,
+					 u64 *start, u64 *end)
+{
+	/* Executable buffers can't start or end on a 4GB boundary */
+	if (!color) {
+		if ((*start & PFN_4G_MASK) == 0)
+			(*start)++;
+
+		if ((*end & PFN_4G_MASK) == 0)
+			(*end)--;
+	}
+}
+
 static int panfrost_probe(struct platform_device *pdev)
 {
 	struct panfrost_device *pfdev;
@@ -394,6 +411,7 @@ static int panfrost_probe(struct platform_device *pdev)
 
 	/* 4G enough for now. can be 48-bit */
 	drm_mm_init(&pfdev->mm, SZ_32M >> PAGE_SHIFT, (SZ_4G - SZ_32M) >> PAGE_SHIFT);
+	pfdev->mm.color_adjust = panfrost_drm_mm_color_adjust;
 
 	pm_runtime_use_autosuspend(pfdev->dev);
 	pm_runtime_set_autosuspend_delay(pfdev->dev, 50); /* ~3 frames */
diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
index df70dcf3cb2f..37ffec8391da 100644
--- a/drivers/gpu/drm/panfrost/panfrost_gem.c
+++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
@@ -66,11 +66,23 @@ static int panfrost_gem_map(struct panfrost_device *pfdev, struct panfrost_gem_o
 {
 	int ret;
 	size_t size = bo->base.base.size;
-	u64 align = size >= SZ_2M ? SZ_2M >> PAGE_SHIFT : 0;
+	u64 align;
+
+	/*
+	 * Executable buffers cannot cross a 16MB boundary as the program
+	 * counter is 24-bits. We assume executable buffers will be less than
+	 * 16MB and aligning executable buffers to their size will avoid
+	 * crossing a 16MB boundary.
+	 */
+	if (!bo->noexec)
+		align = size >> PAGE_SHIFT;
+	else
+		align = size >= SZ_2M ? SZ_2M >> PAGE_SHIFT : 0;
 
 	spin_lock(&pfdev->mm_lock);
 	ret = drm_mm_insert_node_generic(&pfdev->mm, &bo->node,
-					 size >> PAGE_SHIFT, align, 0, 0);
+					 size >> PAGE_SHIFT, align,
+					 bo->noexec, 0);
 	spin_unlock(&pfdev->mm_lock);
 	if (ret)
 		return ret;
@@ -96,6 +108,7 @@ panfrost_gem_create_with_handle(struct drm_file *file_priv,
 		return ERR_CAST(shmem);
 
 	bo = to_panfrost_bo(&shmem->base);
+	bo->noexec = !!(flags & PANFROST_BO_NOEXEC);
 
 	ret = panfrost_gem_map(pfdev, bo);
 	if (ret)
@@ -123,6 +136,7 @@ panfrost_gem_prime_import_sg_table(struct drm_device *dev,
 		return ERR_CAST(obj);
 
 	pobj = to_panfrost_bo(obj);
+	pobj->noexec = true;
 
 	ret = panfrost_gem_map(pfdev, pobj);
 	if (ret)
diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.h b/drivers/gpu/drm/panfrost/panfrost_gem.h
index ce065270720b..132f02399b7b 100644
--- a/drivers/gpu/drm/panfrost/panfrost_gem.h
+++ b/drivers/gpu/drm/panfrost/panfrost_gem.h
@@ -11,7 +11,8 @@ struct panfrost_gem_object {
 	struct drm_gem_shmem_object base;
 
 	struct drm_mm_node node;
-	bool is_mapped;
+	bool is_mapped		:1;
+	bool noexec		:1;
 };
 
 static inline
diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
index 5383b837f04b..d18484a07bfa 100644
--- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
+++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
@@ -212,6 +212,9 @@ int panfrost_mmu_map(struct panfrost_gem_object *bo)
 	if (WARN_ON(bo->is_mapped))
 		return 0;
 
+	if (bo->noexec)
+		prot |= IOMMU_NOEXEC;
+
 	sgt = drm_gem_shmem_get_pages_sgt(obj);
 	if (WARN_ON(IS_ERR(sgt)))
 		return PTR_ERR(sgt);
diff --git a/include/uapi/drm/panfrost_drm.h b/include/uapi/drm/panfrost_drm.h
index b5d370638846..17fb5d200f7a 100644
--- a/include/uapi/drm/panfrost_drm.h
+++ b/include/uapi/drm/panfrost_drm.h
@@ -82,6 +82,8 @@ struct drm_panfrost_wait_bo {
 	__s64 timeout_ns;	/* absolute */
 };
 
+#define PANFROST_BO_NOEXEC	1
+
 /**
  * struct drm_panfrost_create_bo - ioctl argument for creating Panfrost BOs.
  *
-- 
2.20.1

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