Re: [PATCH v6 0/2] MTE support for KVM guest

Mark Rutland
2020-12-03T16:10:50Z

On Fri, Nov 27, 2020 at 03:21:11PM +0000, Steven Price wrote:
> It's been a week, and I think the comments on v5 made it clear that
> enforcing PROT_MTE requirements on the VMM was probably the wrong
> approach. So since I've got swap working correctly without that I
> thought I'd post a v6 which hopefully addresses all the comments so far.
>
> This series adds support for Arm's Memory Tagging Extension (MTE) to
> KVM, allowing KVM guests to make use of it. This builds on the existing
> user space support already in v5.10-rc4, see [1] for an overview.

> arch/arm64/include/asm/kvm_emulate.h | 3 +++
> arch/arm64/include/asm/kvm_host.h | 8 ++++++++
> arch/arm64/include/asm/pgtable.h | 2 +-
> arch/arm64/include/asm/sysreg.h | 3 ++-
> arch/arm64/kernel/mte.c | 18 +++++++++++++-----
> arch/arm64/kvm/arm.c | 9 +++++++++
> arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h | 14 ++++++++++++++
> arch/arm64/kvm/mmu.c | 16 ++++++++++++++++
> arch/arm64/kvm/sys_regs.c | 20 +++++++++++++++-----
> include/uapi/linux/kvm.h | 1 +
> 10 files changed, 82 insertions(+), 12 deletions(-)

I note that doesn't fixup arch/arm64/kvm/inject_fault.c, where in
enter_exception64() we have:

| // TODO: TCO (if/when ARMv8.5-MemTag is exposed to guests)

... and IIUC when MTE is present, TCO should be set when delivering an
exception, so I believe that needs to be updated to set TCO.

Given that MTE-capable HW does that unconditionally, this is going to be
a mess for big.LITTLE. :/

Thanks,
Mark.