[Bug 1907137] Re: LDTR not properly emulated when MTE tag checks enabled at EL0

[Peter Collingbourne]

Thanks for the patch. I've verified that it fixes the assertion failure
with both TCF0=1 and TCF0=2.

You can disregard the kernel panic from comment #1 since it turns out
that it was from an older build of QEMU that did not have 50244cc76abc.

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https://bugs.launchpad.net/bugs/1907137

Title:
  LDTR not properly emulated when MTE tag checks enabled at EL0

Status in QEMU:
  In Progress

Bug description:
  I am trying to boot Android (just the non-GUI parts for now) under
  QEMU with MTE enabled. This can be done by following the instructions
  here to build the fvp-eng target with MTE support:

  
https://cs.android.com/android/platform/superproject/+/master:device/generic/goldfish/fvpbase/

  and launching QEMU with the following command:

  qemu-system-aarch64 -kernel $ANDROID_PRODUCT_OUT/kernel -initrd
  $ANDROID_PRODUCT_OUT/combined-ramdisk.img -machine virt,mte=on -cpu
  max -drive driver=raw,file=$ANDROID_PRODUCT_OUT/system-
  qemu.img,if=none,id=system -device virtio-blk-device,drive=system
  -append "console=ttyAMA0 earlyprintk=ttyAMA0
  androidboot.hardware=fvpbase
  androidboot.boot_devices=a003e00.virtio_mmio loglevel=9
  printk.devkmsg=on buildvariant=eng" -m 512 -nographic -no-reboot

  If I do this then QEMU crashes like so:

  **
  ERROR:../target/arm/mte_helper.c:558:mte_check_fail: code should not be 
reached
  Bail out! ERROR:../target/arm/mte_helper.c:558:mte_check_fail: code should 
not be reached

  The error is caused by an MTE tag check fault from an LDTR instruction
  in __arch_copy_from_user. At this point TCF=0 and TCF0=2.

  I have this patch that gets me past the error but it is unclear
  whether this is the correct fix since there may be other confusion
  between TCF and TCF0 elsewhere.

  diff --git a/target/arm/mte_helper.c b/target/arm/mte_helper.c
  index 153bd1e9df..aa5db4eac4 100644
  --- a/target/arm/mte_helper.c
  +++ b/target/arm/mte_helper.c
  @@ -552,10 +552,8 @@ static void mte_check_fail(CPUARMState *env, uint32_t 
desc,
       case 0:
           /*
            * Tag check fail does not affect the PE.
  -         * We eliminate this case by not setting MTE_ACTIVE
  -         * in tb_flags, so that we never make this runtime call.
            */
  -        g_assert_not_reached();
  +        break;
   
       case 2:
           /* Tag check fail causes asynchronous flag set.  */

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