On 25/01/16 16:26, Will Deacon wrote:

On Mon, Jan 25, 2016 at 03:53:34PM +0000, Marc Zyngier wrote:

quoted

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.

[...]

quoted

 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.

I did use HW breakpoints on the model by hacking the host kernel to
return Debug Version 6 instead of 7, and things seem to work as
expected. strace also works out of the box.

As for perf, did you have something precise in mind?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...