[Bug 1863685] Re: ARM: HCR.TSW traps are not implemented

[Julien Freche]

Thanks for the quick turn around! I tested both your patches together
(it's useful to have both to emulate set/way flushing inside a guest)
and I am getting something unexpected. At some point, we are trapping on
an access to DACR but ESR_EL2 doesn't seem to make a lot of sense:
0xfe00dc0. I am running a 32-bit Linux inside a VM.

Decoding it: Rt is set to 0xe which is LR_usr. Also, this is a read
operation. So, essentially the guest seems to try to set DACR to LR_usr
which seems unreasonable.

It could be an issue with the hypervisor on my side (I am running some
custom code). But, it's not obvious to me and the code behaves fine on
bare-metal. Is there a chance that ESR is not populated correctly?

In any case, I do see traps for set/way instructions so, from that point
of view, the patch is good.

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https://bugs.launchpad.net/bugs/1863685

Title:
  ARM: HCR.TSW traps are not implemented

Status in QEMU:
  In Progress

Bug description:
  On 32-bit and 64-bit ARM platforms, setting HCR.TSW is supposed to
  "Trap data or unified cache maintenance instructions that operate by
  Set/Way." Quoting the ARM manual:

  If EL1 is using AArch64 state, accesses to DC ISW, DC CSW, DC CISW are 
trapped to EL2, reported using EC syndrome value 0x18.
  If EL1 is using AArch32 state, accesses to DCISW, DCCSW, DCCISW are trapped 
to EL2, reported using EC syndrome value 0x03.

  However, QEMU does not trap those instructions/registers. This was
  tested on the branch master of the git repo.

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