Am 26.06.24 um 10:05 schrieb Jason-JH Lin (林睿祥):
In the step 3), we need to verify the dma-buf is allocated from
"restricted_mtk_cma", but there is no way to pass the secure flag
or
private data from userspace to the import interface in DRM driver.
Why do you need to verify that?
I need to know the imported buffer is allocated from restricted cma and
mark it as a secure buffer in mediatek-drm driver. Then, I will add
some configuration to the hardware if the buffer is secure buffer, so
that it can get the permission to access the secure buffer.
Yeah so far that makes sense. This is basically what other drivers do
with secure buffers as well.
But why do you want the kernel to transport that information? Usually
drivers get the information from userspace what to do with a buffer.
In other words the format, stride, tilling and also if it's a secure
buffer or not comes from userspace.
What the hardware usually handles internally is things like encryption
keys, but you eventually get the information where to look for the key
from userspace as well.
Handling inside the kernel would only be necessary if userspace could
for example crash the system with invalid parameters. But for encryption
that is usually not the case.
So I can only verify it like this now:
struct drm_gem_object *mtk_gem_prime_import_sg_table(struct
drm_device
*dev, struct dma_buf_attachment *attach, struct sg_table *sg)
{
struct mtk_gem_obj *mtk_gem;
/* check if the entries in the sg_table are contiguous */
if (drm_prime_get_contiguous_size(sg) < attach->dmabuf->size) {
DRM_ERROR("sg_table is not contiguous");
return ERR_PTR(-EINVAL);
}
mtk_gem = mtk_gem_init(dev, attach->dmabuf->size);
if (IS_ERR(mtk_gem))
return ERR_CAST(mtk_gem);
- mtk_gem->secure = (!strncmp(attach->dmabuf->exp_name,
"restricted",
10));
mtk_gem->dma_addr = sg_dma_address(sg->sgl);
mtk_gem->size = attach->dmabuf->size;
mtk_gem->sg = sg;
return &mtk_gem->base;
}
Complete NAK from my side to that approach. Importing of a DMA-buf
should be independent of the exporter.
What you could do is to provide the secure buffer from a device and
not a device heap.
You mean I should allocate buffer in mediate-drm driver not userspace?
Well that depends. The question is if you have multiple drivers which
needs to work with this secure buffer?
If yes then you should have a general allocation heap for it. If no then
the buffers could as well be allocated from the driver interface directly.
I just have modified this to userspace by the comment here:
https://patchwork.kernel.org/project/linux-mediatek/patch/20240403102701.369...
I think I have the same problem as the ECC_FLAG mention in:
https://lore.kernel.org/linux-media/20240515-dma-buf-ecc-heap-v1-0-54cbbd049...
I think it would be better to have the user configurable private
information in dma-buf, so all the drivers who have the same
requirement can get their private information from dma-buf directly
and
no need to change or add the interface.
What's your opinion in this point?
Well of hand I don't see the need for that.
What happens if you get a non-secure buffer imported in your secure
device?
We use the same mediatek-drm driver for secure and non-secure buffer.
If non-secure buffer imported to mediatek-drm driver, it's go to the
normal flow with normal hardware settings.
We use different configurations to make hardware have different
permission to access the buffer it should access.
So if we can't get the information of "the buffer is allocated from
restricted_mtk_cma" when importing the buffer into the driver, we won't
be able to configure the hardware correctly.
Why can't you get this information from userspace?
Regards,
Christian.
Regards,
Jason-JH.Lin
Regards,
Christian.
Regards,
Jason-JH.Lin
Regards,
Christian.
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The information contained in this e-mail message (including any
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conveyed only to the designated recipient(s). Any use, dissemination,
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Christian König
Daniel Vetter