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id = 1057
title = "AArch64: ISV is set to 1 in ESR_EL2 when taking a data abort with post-indexed instructions"
state = "closed"
created_at = "2022-06-02T20:50:04.695Z"
closed_at = "2022-07-18T16:47:38.098Z"
labels = ["accel: TCG", "target: arm", "workflow::In Progress"]
url = "https://gitlab.com/qemu-project/qemu/-/issues/1057"
host-os = "MacOS 12.4"
host-arch = "ARM64"
qemu-version = "QEMU emulator version 7.0.0"
guest-os = "Custom - BedRock Hypervisor running with the NOVA microkernel"
guest-arch = "ARMv8"
description = """I think that I have a Qemu bug in my hands, but, I could still be missing something. Consider the following instruction:
`0x0000000000000000: C3 44 00 B8 str w3, [x6], #4`
notice the last #4, I think this is what we would call a post-indexed instruction (falls into the category of instructions with writeback). As I understand it, those instructions should not have ISV=1 in ESR_EL2 when faulting.
Here is the relevant part of the manual:
```
For other faults reported in ESR_EL2, ISV is 0 except for the following stage 2 aborts:
• AArch64 loads and stores of a single general-purpose register (including the register specified with 0b11111, including those with Acquire/Release semantics, but excluding Load Exclusive or Store Exclusive and excluding those with writeback).
```
However, I can see that Qemu sets ISV to 1 here. The ARM hardware that I tested gave me a value of ISV=0 for similar instructions.
Another example of instruction: `0x00000000000002f8: 01 1C 40 38 ldrb w1, [x0, #1]!`"""
reproduce = """1. Run some hypervisor in EL2
2. Create a guest running at EL1 that executes one of the mentioned instructions (and make the instruction fault by writing to some unmapped page in SLP)
3. Observe the value of ESR_EL2 on data abort
Unfortunately, I cannot provide an image to reproduce this (the software is not open-source). But, I would be happy to help test a patch."""
additional = "n/a"
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