Am 04.09.19 um 10:19 schrieb Thomas Hellström (VMware): > 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. Why? Because we don't use dma_mmap_coherent()? I've already talked with Christoph that we probably want to switch TTM over to using that instead to also get rid of the ttm_io_prot() hack. Regards, Christian. > > 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? > > /Thomas > > >> >> Regards, >> Christian. > > _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
