Writing to UART mapped memory address

[Stefan Kalkowski]

On 06/27/2017 12:21 PM, rijurekha at ...71... wrote:
> In base-hw/src/core/spec/arm_v7/trustzone/mode_transition.s,
> _nonsecure_kernel_entry:, where we go in the monitor handler after a DABT,
> we have
> mov   r1, #0
> mcr   p15, 0, r1, c1, c1, 0 //sets SCR all 0s
> cps #SVC_MODE //changes processor mode to SVC
> 
> In base-hw/src/core/spec/arm_v7/trustzone/kernel/vm.cc,
> in void Vm::exception(unsigned const cpu),
> case Genode::Cpu_state::DATA_ABORT:,
> Cpu::Scr::read() gives 00000000 and Cpu::Psr::read() gives 600001d3. So
> the NS bit in Scr is 0 and the mode bits in CPSR are 10011=19, which is
> the SVC mode. So we are getting the correct values that the monitor DABT
> handler sets.
> 
> We are in the secure SVC mode, when we try to access the  uart physical
> address. So what is causing a data abort now?

No, you are in secure SVC mode within the kernel when entering this
exception routine. Your access within the tz_vmm component is in secure
USR mode.

Anyway, I doubt that it has something to do with kernel/user
secure/non-secure issues, because otherwise all other userland drivers
should fault too. Another possibility is that the page-table entries are
not refering to the right address due to some wrong semantics in your
added code.
Or it is mapped with different caching attributes in kernel and
user-land (please: do not use the device in kernel and userland), but I
can't imagine how, if it's really an IOMEM dataspace in your code.
Well, to be honest, I do not know, why it should fail, but again it
would help if you provide a working branch.

Regards Stefan

> 
> Thanks!
> Riju
> 
> 
> 
> 
> 
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-- 
Stefan Kalkowski
Genode Labs

https://github.com/skalk · http://genode.org/