Messages in this thread | | | Subject | Re: [PATCH] arm64: tegra: only map accessible sysram | From | Stephen Warren <> | Date | Wed, 2 Oct 2019 14:30:53 -0600 |
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On 9/30/19 4:02 AM, Mian Yousaf Kaukab wrote: > On Sun, Sep 29, 2019 at 11:28:43PM -0600, Stephen Warren wrote: >> On 9/29/19 2:08 PM, Mian Yousaf Kaukab wrote: >>> Most of the SysRAM is secure and only accessible by TF-A. >>> Don't map this inaccessible memory in kernel. Only map pages >>> used by bpmp driver. >> >> I don't believe this change is correct. The actual patch doesn't >> implement mapping a subset of the RAM (a software issue), but rather it >> changes the DT representation of the SYSRAM hardware. The SYSRAM >> hardware always does start at 0x30000000, even if a subset of the >> address range is dedicated to a specific purpose. If the kernel must map >> only part of the RAM, then some additional property should indicate >> this.[...] > I agree the hardware description becomes inaccurate with this change. > > In the current setup complete 0x3000_0000 to 0x3005_0000 range is being mapped > as normal memory (MT_NORMAL_NC). Though only 0x3004_E000 to 0x3005_0000 are > accessible by the kernel.
Nit: I expect that a much larger region than that is *accessible*, although it's quite plausible that only that region is actually *accessed*/used right now.
> I am seeing an issue where a read access (which I > believe is speculative) to inaccessible range causes an SError. Another > solution for this problem could be to add "no-memory-wc" to SysRAM node so that > it is mapped as device memory (MT_DEVICE_nGnRE). Would that be acceptable?
Why does the driver blindly map the entire memory at all? Surely it should only map the portions of RAM that other drivers request/use? And surely the BPMP driver or DT node is already providing that information?
But yes, changing the mapping type to avoid speculation might be an acceptable solution for now, although I think we'd want to work things out better later. I don't know if there would be any impact to the BPMP driver related to the slower SRAM access due to this change. Best consult a BPMP expert or Tegra maintainer about that.
>> [...] Also, I believe it's incorrect to hard-code into the kernel's DT >> the range of addresses used by the secure monitor/OS, since this can >> vary depending on what the user actually chooses to install as the >> secure monitor/OS. Any indication of such regions should be filled in at >> runtime by some boot firmware or the secure monitor/OS itself, or >> retrieved using some runtime API rather than DT. > Secure-OS addresses are not of interest here. SysRAM is partitioned > between secure-OS and BPMP and kernel is only interested in the BPMP > part. The firmware can update these addresses in the device-tree if it > wants to. Would you prefer something similar implemented in u-boot so > that it updates SysRAM node to only expose kernel accessible part of it > to the kernel? > > Can u-boot dynamically figure out the Secure-OS vs BPMP partition? > > BR, > Yousaf >
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