Re: [PATCH 00/15] arm/arm64: KVM: Merge boot and runtime page tables

Christoffer Dall
2016-06-27T13:29:23Z

On Tue, Jun 07, 2016 at 11:58:20AM +0100, Marc Zyngier wrote:
> Until now, we've been setting up KVM using two sets of page tables:
> one for the "boot" where we perform the basic MMU setup, and one for
> the runtime.
>
> Switching between the two was though to be safe, but we've recently
> realized that it is not: it is not enough to ensure that the VA->PA
> mapping is consistent when switching TTBR0_EL2, but we also have to
> ensure that the intermediate translations are the same as well. If the
> TLB can return two different values for intermediate translations,
> we're screwed (TLB conflicts).

Just a clarification: Intermediate Translations here means the
page table levels of translations for a single stage of translation?

Is there a valid reference to the arhictecture specification for this?

Thanks,
-Christoffer

>
> At that point, the only safe thing to do is to never change TTBR0_EL2,
> which means that we need to make the idmap page part of the runtime
> page tables.
>
> The series starts with a bit of brain dumping explaining what we're
> trying to do. This might not be useful as a merge candidate, but it
> was useful for me to put this somewhere. It goes on revamping the
> whole notion of HYP VA range, making it runtime patchable. It then
> always merge idmap and runtime page table into one set, leading to
> quite a lot of simplification in the init/teardown code. In the
> process, 32bit KVM gains the ability to teardown the HYP page-tables
> and vectors, which makes kexec a bit closer.
>
> This has been tested on Seattle, Juno, the FVP model (both v8.0 and
> v8.1), Cubietruck and Midway, and is based on 4.7-rc2.
>
> Thanks,
>
> M.
>
> Marc Zyngier (15):
> arm64: KVM: Merged page tables documentation
> arm64: KVM: Kill HYP_PAGE_OFFSET
> arm64: Add ARM64_HYP_OFFSET_LOW capability
> arm64: KVM: Define HYP offset masks
> arm64: KVM: Refactor kern_hyp_va/hyp_kern_va to deal with multiple
> offsets
> arm/arm64: KVM: Export __hyp_text_start/end symbols
> arm64: KVM: Runtime detection of lower HYP offset
> arm/arm64: KVM: Always have merged page tables
> arm64: KVM: Simplify HYP init/teardown
> arm/arm64: KVM: Drop boot_pgd
> arm/arm64: KVM: Kill free_boot_hyp_pgd
> arm: KVM: Simplify HYP init
> arm: KVM: Allow hyp teardown
> arm/arm64: KVM: Prune unused #defines
> arm/arm64: KVM: Check that IDMAP doesn't intersect with VA range
>
> arch/arm/include/asm/kvm_asm.h | 2 +
> arch/arm/include/asm/kvm_host.h | 25 +++-----
> arch/arm/include/asm/kvm_mmu.h | 11 ----
> arch/arm/include/asm/virt.h | 4 ++
> arch/arm/kvm/arm.c | 20 ++----
> arch/arm/kvm/init.S | 56 ++++++----------
> arch/arm/kvm/mmu.c | 125 ++++++++++++++++--------------------
> arch/arm64/include/asm/cpufeature.h | 3 +-
> arch/arm64/include/asm/kvm_host.h | 17 ++---
> arch/arm64/include/asm/kvm_hyp.h | 28 ++++----
> arch/arm64/include/asm/kvm_mmu.h | 100 ++++++++++++++++++++++++-----
> arch/arm64/include/asm/virt.h | 4 ++
> arch/arm64/kernel/cpufeature.c | 19 ++++++
> arch/arm64/kvm/hyp-init.S | 61 +++---------------
> arch/arm64/kvm/hyp/entry.S | 19 ------
> arch/arm64/kvm/hyp/hyp-entry.S | 15 +++++
> arch/arm64/kvm/reset.c | 28 --------
> 17 files changed, 240 insertions(+), 297 deletions(-)
>
> --
> 2.1.4
>