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

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