On 9/4/19 10:19 AM, Thomas Hellström (VMware) wrote:
Hi, Christian,
On 9/4/19 9:33 AM, Koenig, Christian wrote:
Am 03.09.19 um 23:05 schrieb Thomas Hellström (VMware):
On 9/3/19 10:51 PM, Dave Hansen wrote:
On 9/3/19 1:36 PM, Thomas Hellström (VMware) wrote:
So the question here should really be, can we determine already at
mmap
time whether backing memory will be unencrypted and adjust the *real*
vma->vm_page_prot under the mmap_sem?
Possibly, but that requires populating the buffer with memory at mmap
time rather than at first fault time.
I'm not connecting the dots.
vma->vm_page_prot is used to create a VMA's PTEs regardless of if they
are created at mmap() or fault time. If we establish a good
vma->vm_page_prot, can't we just use it forever for demand faults?
With SEV I think that we could possibly establish the encryption flags
at vma creation time. But thinking of it, it would actually break with
SME where buffer content can be moved between encrypted system memory
and unencrypted graphics card PCI memory behind user-space's back.
That would imply killing all user-space encrypted PTEs and at fault
time set up new ones pointing to unencrypted PCI memory..
Well my problem is where do you see encrypted system memory here?
At least for AMD GPUs all memory accessed must be unencrypted and that
counts for both system as well as PCI memory.
We're talking SME now right?
The current SME setup is that if a device's DMA mask says it's capable
of addressing the encryption bit, coherent memory will be encrypted.
The memory controllers will decrypt for the device on the fly.
Otherwise coherent memory will be decrypted.
So I don't get why we can't assume always unencrypted and keep it
like that.
I see two reasons. First, it would break with a real device that
signals it's capable of addressing the encryption bit.
Second I can imagine unaccelerated setups (something like vkms using
prime feeding a VNC connection) where we actually want the TTM buffers
encrypted to protect data.
But at least the latter reason is way far out in the future.
So for me I'm ok with that if that works for you?
Hmm, BTW,
Are you sure the AMD GPUs use unencrypted system memory rather than
relying on the memory controllers to decrypt?
In that case it seems strange that they get away with encrypted TTM
PTEs, whereas vmwgfx don't...
/Thomas
/Thomas
Regards,
Christian.
_______________________________________________
dri-devel mailing list
dri-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/dri-devel
