Re: [PATCH 1/2] KVM: arm64: Initialise TCR2_EL2 for nVHE mode

On Fri, 04 Sep 2026 12:35:22 +0100,
Mark Brown [off-list ref] wrote:

On Fri, Sep 04, 2026 at 08:32:04AM +0100, Marc Zyngier wrote:

quoted

Mark Brown [off-list ref] wrote:

quoted

quoted

+alternative_if ARM64_HAS_TCR2
+	/*
+	 * Disable any features we enabled in case the next user doesn't
+	 * have TCR2_EL2 support.
+	 */
+	msr	REG_TCR2_EL2, xzr
+alternative_else_nop_endif

quoted

I don't see the point of this. The MMU is off, and if the next piece
of SW can't correctly initialise the HW, that's its problem.

So we don't care about reverting back to users who are just plain
unaware of the register?  In practice for Linux that's fairly old
kernels, but people might feel adverturous and try or try some non-Linux
thing.  This stuff is all a bit edge casey with what we support.

I certainly do not care. If you kexec an ancient kernel on new HW and
can't correctly initialise it, you lose. Don't do that.

	M.

-- 
Jazz isn't dead. It just smells funny.