Re: [PATCH v2 00/21] arm64: Virtualization Host Extension support
From: Will Deacon
Date: Mon Jan 25 2016 - 11:44:44 EST
On Mon, Jan 25, 2016 at 04:37:39PM +0000, Marc Zyngier wrote:
> On 25/01/16 16:26, Will Deacon wrote:
> > 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.
> 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?
It would be worth trying things like the filter options on perf events
(perf stat -e cycles:k to count cycles in kernel space) and also
breakpoints (perf stat -e mem:<addr>:rwx on kernel addresses).