On Thu, Apr 08, 2021 at 11:31:42AM +0100, Marc Zyngier wrote:

On 2021-04-07 22:18, Will Deacon wrote:

quoted

On Tue, Mar 30, 2021 at 06:39:47PM +0100, Marc Zyngier wrote:

quoted

CPUs stuck in VHE mode need some additional care if the kernel
is compiled without CONFIG_ARM64_VHE.

Treat this case as another version of a mismatched boot, and
prevent KVM from being initialised. The machine will boot in
some bizarre state, using TPIDR_EL1 instead of TPIDR_EL2, but
otherwise be functional.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/include/asm/virt.h | 18 +++++++++++++-----
 arch/arm64/kvm/va_layout.c    |  9 +++++++++
 2 files changed, 22 insertions(+), 5 deletions(-)

Hmm, I think we definitely need _something_ here, but it's a bit
annoying
to put ourselves into this weird state just for the sake of one stupid
machine.

Which is why I'm not keen at all on this patch, and I'm happy to see
the machine die a painful death. We really can't be blamed for terminally
buggy HW, which the M1 obviously is.

Perhaps, but it's not clear at all how the problem manifests and so we
_will_ be blamed when things go wonky, especially as the real culprits
all seem to be hiding...

quoted

What if we dropped CONFIG_ARM64_VHE and made the VHE code unconditional
instead? Is there a good reason to allow it to be disabled nowadays?

What do we do for the other camp, aka people really wanting to run nVHE
without any command line parameter? I can't see why you'd want to do
that, but hey, that's only me.

They can pass the command-line parameter, no? If we ever get CMDLINE_EXTEND
support back, they could even add it in there!

I'd be quite happy to see CONFIG_ARM64_VHE go though. Let me know if you
want a patch doing that instead.

Yes please.

Will

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