Re: [PATCH v2 00/21] arm64: Virtualization Host Extension support

From: Will Deacon
Date: Mon Jan 25 2016 - 11:26:56 EST


On Mon, Jan 25, 2016 at 03:53:34PM +0000, Marc Zyngier wrote:
> ARMv8.1 comes with the "Virtualization Host Extension" (VHE for
> short), which enables simpler support of Type-2 hypervisors.
>
> This extension allows the kernel to directly run at EL2, and
> significantly reduces the number of system registers shared between
> host and guest, reducing the overhead of virtualization.
>
> In order to have the same kernel binary running on all versions of the
> architecture, this series makes heavy use of runtime code patching.
>
> The first 20 patches massage the KVM code to deal with VHE and enable
> Linux to run at EL2. The last patch catches an ugly case when VHE
> capable CPUs are paired with some of their less capable siblings. This
> should never happen, but hey...
>
> I have deliberately left out some of the more "advanced"
> optimizations, as they are likely to distract the reviewer from the
> core infrastructure, which is what I care about at the moment.
>
> A few things to note:
>
> - Given that the code has been almost entierely rewritten, I've
> dropped all Acks from the new patches
>
> - GDB is currently busted on VHE systems, as it checks for version 6
> on the debug architecture, while VHE is version 7. The binutils
> people are on the case.

[...]

> arch/arm/include/asm/virt.h | 5 ++
> arch/arm/kvm/arm.c | 151 +++++++++++++++++++------------
> arch/arm/kvm/mmu.c | 7 ++
> arch/arm64/Kconfig | 13 +++
> arch/arm64/include/asm/cpufeature.h | 3 +-
> arch/arm64/include/asm/kvm_arm.h | 1 +
> arch/arm64/include/asm/kvm_emulate.h | 3 +
> arch/arm64/include/asm/kvm_mmu.h | 34 ++++++-
> arch/arm64/include/asm/virt.h | 27 ++++++
> arch/arm64/kernel/asm-offsets.c | 3 -
> arch/arm64/kernel/cpufeature.c | 15 +++-
> arch/arm64/kernel/head.S | 51 ++++++++++-
> arch/arm64/kernel/smp.c | 3 +
> arch/arm64/kvm/hyp-init.S | 18 +---
> arch/arm64/kvm/hyp.S | 7 ++
> arch/arm64/kvm/hyp/entry.S | 6 ++
> arch/arm64/kvm/hyp/hyp-entry.S | 107 +++++++---------------
> arch/arm64/kvm/hyp/hyp.h | 119 ++++++++++++++++++++++--
> arch/arm64/kvm/hyp/switch.c | 170 +++++++++++++++++++++++++++++++----
> arch/arm64/kvm/hyp/sysreg-sr.c | 147 ++++++++++++++++++++----------
> arch/arm64/kvm/hyp/timer-sr.c | 10 +--
> drivers/clocksource/arm_arch_timer.c | 96 ++++++++++++--------
> 22 files changed, 724 insertions(+), 272 deletions(-)

Have you tried hw_breakpoint/perf/ptrace with these changes? I was under
the impression that the debug architecture was aware of E2H and did need
some changes made. I know you say that GDB is broken anyway, but we should
check that the kernel does the right thing if userspace pokes it the
right way.

Will