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

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On Monday 25 January 2016 16:23:37 Marc Zyngier wrote:
> On 25/01/16 16:15, Arnd Bergmann wrote:
> > On Monday 25 January 2016 15:53:34 Marc Zyngier wrote:
> >> 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.
> > 
> > One question: as you mention that you use a lot of runtime code patching
> > to make this work transparently, how does this compare to runtime patching
> > the existing kernel to run in EL2 mode without VHE? Is that even possible?
> 
> I haven't explored that particular avenue - by the look of it, this
> would require a lot more work, as v8.0 EL2 lacks a number of features
> that Linux currently requires (like having two TTBRs, for example).

Ok, I see.

> > My interpretation so far as always been "that's too complicated to
> > do because it would require a lot of runtime patching", but now we seem
> > to get that anyway because we want to run a hypervisor-enabled kernel in
> > either EL1 or EL2 depending on the presence of another feature.
> 
> The kernel itself is mostly untouched (what runs at EL1 also runs at EL2
> without any patching, because the new EL2 is now a superset of EL1). It
> is the hypervisor code that gets a beating with the code-patching stick.

Thanks for the explanation, makes sense.

	Arnd

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[PATCH v2 00/21] arm64: Virtualization Host Extension support Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:00 +0100
  [PATCH v2 16/21] arm64: KVM: VHE: Add fpsimd enabling on guest access Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:00 +0100
  [PATCH v2 09/21] arm64: KVM: VHE: Differenciate host/guest sysreg save/restore Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:00 +0100
  [PATCH v2 06/21] arm64: KVM: VHE: Patch out use of HVC Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:00 +0100
  [PATCH v2 15/21] arm64: KVM: VHE: Use unified sysreg accessors for timer Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:00 +0100
  [PATCH v2 21/21] arm64: Panic when VHE and non VHE CPUs coexist Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:00 +0100
    Re: [PATCH v2 21/21] arm64: Panic when VHE and non VHE CPUs coexist "Suzuki K. Poulose" <Suzuki.Poulose@arm.com> - 2016-01-26 15:30 +0100
      Re: [PATCH v2 21/21] arm64: Panic when VHE and non VHE CPUs coexist Marc Zyngier <marc.zyngier@arm.com> - 2016-01-26 15:40 +0100
  [PATCH v2 10/21] arm64: KVM: VHE: Split save/restore of sysregs shared between EL1 and EL2 Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:00 +0100
  [PATCH v2 20/21] arm64: VHE: Add support for running Linux in EL2 mode Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:00 +0100
    Re: [PATCH v2 20/21] arm64: VHE: Add support for running Linux in EL2  mode "Suzuki K. Poulose" <Suzuki.Poulose@arm.com> - 2016-01-26 15:10 +0100
      Re: [PATCH v2 20/21] arm64: VHE: Add support for running Linux in EL2  mode "Suzuki K. Poulose" <Suzuki.Poulose@arm.com> - 2016-01-26 15:40 +0100
  [PATCH v2 17/21] arm64: KVM: VHE: Add alternative panic handling Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:00 +0100
  [PATCH v2 05/21] arm64: KVM: VHE: Turn VTCR_EL2 setup into a reusable macro Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:00 +0100
  [PATCH v2 11/21] arm64: KVM: VHE: Use unified system register accessors Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:10 +0100
  [PATCH v2 03/21] arm64: Add ARM64_HAS_VIRT_HOST_EXTN feature Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:10 +0100
  [PATCH v2 08/21] arm64: KVM: VHE: Introduce unified system register accessors Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:10 +0100
  [PATCH v2 04/21] arm64: KVM: Skip HYP setup when already running in HYP Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:10 +0100
  [PATCH v2 02/21] arm64: Allow the arch timer to use the HYP timer Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:10 +0100
  [PATCH v2 13/21] arm64: KVM: VHE: Make __fpsimd_enabled VHE aware Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:10 +0100
  [PATCH v2 14/21] arm64: KVM: VHE: Implement VHE activate/deactivate_traps Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:10 +0100
  [PATCH v2 07/21] arm64: KVM: VHE: Patch out kern_hyp_va Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:10 +0100
  Re: [PATCH v2 00/21] arm64: Virtualization Host Extension support Arnd Bergmann <arnd@arndb.de> - 2016-01-25 17:20 +0100
    Re: [PATCH v2 00/21] arm64: Virtualization Host Extension support Arnd Bergmann <arnd@arndb.de> - 2016-01-25 17:30 +0100
    Re: [PATCH v2 00/21] arm64: Virtualization Host Extension support Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:30 +0100
  Re: [PATCH v2 00/21] arm64: Virtualization Host Extension support Will Deacon <will.deacon@arm.com> - 2016-01-25 17:30 +0100
    Re: [PATCH v2 00/21] arm64: Virtualization Host Extension support Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 17:40 +0100
      Re: [PATCH v2 00/21] arm64: Virtualization Host Extension support Will Deacon <will.deacon@arm.com> - 2016-01-25 17:50 +0100
        Re: [PATCH v2 00/21] arm64: Virtualization Host Extension support Marc Zyngier <marc.zyngier@arm.com> - 2016-01-25 20:20 +0100

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