Re: [PATCH v4 00/23] arm64: Virtualization Host Extension support

From: "Alex Bennée" <alex.bennee@linaro.org>
To: Marc Zyngier <marc.zyngier@arm.com>
Cc: kvm@vger.kernel.org, Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH v4 00/23] arm64: Virtualization Host Extension support
Date: Mon, 29 Feb 2016 17:43:28 +0000	[thread overview]
Message-ID: <871t7vjttr.fsf@linaro.org> (raw)
In-Reply-To: <1455216004-19499-1-git-send-email-marc.zyngier@arm.com>

Marc Zyngier <marc.zyngier@arm.com> writes:

> 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 22 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.
>
> Note: 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.

I assume you are talking about ptrace debug here rather than guest
debug?

Anyway from a cursory inspection I didn't see anything to worry about
from the guest debug side which is unchanged.

Acked-by: Alex Bennée <alex.bennee@linaro.org>

>
> This has been tested on the FVP_Base_SLV-V8-A model, and based on
> v4.5-rc3 + kvmarm/master. I've put a branch out on:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git kvm-arm64/vhe
>
> * From v3:
>   - Cleaned debug handling after comments from Catalin
>   - Added missing barriers in the panic patch
>   - Collected Rb and Acks from Christoffer and Catalin
>
> * From v2:
>   - Added support for perf to count kernel events in EL2
>   - Added support for EL2 breakpoints
>   - Moved the VTCR_EL2 setup from assembly to C
>   - Made the fault handling easier to understand (hopefuly)
>   - Plenty of smaller fixups
>
> * From v1:
>   - Full rewrite now that the World Switch is written in C code.
>   - Dropped the "early IRQ handling" for the moment.
>
> Marc Zyngier (23):
>   arm/arm64: KVM: Add hook for C-based stage2 init
>   arm64: KVM: Switch to C-based stage2 init
>   arm/arm64: Add new is_kernel_in_hyp_mode predicate
>   arm64: Allow the arch timer to use the HYP timer
>   arm64: Add ARM64_HAS_VIRT_HOST_EXTN feature
>   arm64: KVM: Skip HYP setup when already running in HYP
>   arm64: KVM: VHE: Patch out use of HVC
>   arm64: KVM: VHE: Patch out kern_hyp_va
>   arm64: KVM: VHE: Introduce unified system register accessors
>   arm64: KVM: VHE: Differenciate host/guest sysreg save/restore
>   arm64: KVM: VHE: Split save/restore of registers shared between guest
>     and host
>   arm64: KVM: VHE: Use unified system register accessors
>   arm64: KVM: VHE: Enable minimal sysreg save/restore
>   arm64: KVM: VHE: Make __fpsimd_enabled VHE aware
>   arm64: KVM: VHE: Implement VHE activate/deactivate_traps
>   arm64: KVM: VHE: Use unified sysreg accessors for timer
>   arm64: KVM: VHE: Add fpsimd enabling on guest access
>   arm64: KVM: VHE: Add alternative panic handling
>   arm64: KVM: Move most of the fault decoding to C
>   arm64: perf: Count EL2 events if the kernel is running in HYP
>   arm64: hw_breakpoint: Allow EL2 breakpoints if running in HYP
>   arm64: VHE: Add support for running Linux in EL2 mode
>   arm64: Panic when VHE and non VHE CPUs coexist
>
>  arch/arm/include/asm/kvm_host.h        |   4 +
>  arch/arm/include/asm/virt.h            |   5 +
>  arch/arm/kvm/arm.c                     | 174 ++++++++++++++++++----------
>  arch/arm/kvm/mmu.c                     |   7 ++
>  arch/arm64/Kconfig                     |  13 +++
>  arch/arm64/include/asm/cpufeature.h    |   3 +-
>  arch/arm64/include/asm/hw_breakpoint.h |  49 +++++---
>  arch/arm64/include/asm/kvm_arm.h       |   6 +-
>  arch/arm64/include/asm/kvm_asm.h       |   2 +
>  arch/arm64/include/asm/kvm_emulate.h   |   3 +
>  arch/arm64/include/asm/kvm_host.h      |   6 +
>  arch/arm64/include/asm/kvm_mmu.h       |  12 +-
>  arch/arm64/include/asm/virt.h          |  27 +++++
>  arch/arm64/kernel/asm-offsets.c        |   3 -
>  arch/arm64/kernel/cpufeature.c         |  11 ++
>  arch/arm64/kernel/head.S               |  50 +++++++-
>  arch/arm64/kernel/perf_event.c         |  14 ++-
>  arch/arm64/kernel/smp.c                |   3 +
>  arch/arm64/kvm/hyp-init.S              |  18 ---
>  arch/arm64/kvm/hyp.S                   |   7 ++
>  arch/arm64/kvm/hyp/Makefile            |   1 +
>  arch/arm64/kvm/hyp/entry.S             |   6 +
>  arch/arm64/kvm/hyp/hyp-entry.S         | 109 ++++++------------
>  arch/arm64/kvm/hyp/hyp.h               | 108 ++++++++++++++++--
>  arch/arm64/kvm/hyp/s2-setup.c          |  44 +++++++
>  arch/arm64/kvm/hyp/switch.c            | 202 +++++++++++++++++++++++++++++----
>  arch/arm64/kvm/hyp/sysreg-sr.c         | 147 ++++++++++++++++--------
>  arch/arm64/kvm/hyp/timer-sr.c          |  10 +-
>  drivers/clocksource/arm_arch_timer.c   |  96 ++++++++++------
>  29 files changed, 842 insertions(+), 298 deletions(-)
>  create mode 100644 arch/arm64/kvm/hyp/s2-setup.c

--
Alex Bennée
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