Re: [PATCH v2] arm64:kgdb: Fix kernel single-stepping

From: Marc Zyngier
Date: Thu Feb 20 2020 - 09:21:41 EST

On 2020-02-19 15:24, minyard@xxxxxxx wrote:
From: Corey Minyard <cminyard@xxxxxxxxxx>


After studying the EL0 handling for this, I realized an issue with using
MDSCR to check if single step is enabled: it can be expensive on a VM.
So check the task flag first to see if single step is enabled. Then
check MDSCR if the task flag is set.

Very tangential remark: I'd really like people *not* to try and optimize
Linux based on the behaviour of a hypervisor. In general, reading a
system register is fast, and the fact that it traps on a given hypervisor
at some point may not be true in the future, nor be a valid assumption
across hypervisors.

Jazz is not dead. It just smells funny...