linux-kernel - Re: [PATCH v2 00/11] arm64: ptdump: View the second stage page-tables

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Message-ID: <ZTI4FcFkgwnLv0-1@google.com>
Date:   Fri, 20 Oct 2023 09:19:33 +0100
From:   Vincent Donnefort <vdonnefort@...gle.com>
To:     Sebastian Ene <sebastianene@...gle.com>
Cc:     will@...nel.org, catalin.marinas@....com, mark.rutland@....com,
        akpm@...ux-foundation.org, maz@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com, qperret@...gle.com, smostafa@...gle.com
Subject: Re: [PATCH v2 00/11] arm64: ptdump: View the second stage page-tables

On Thu, Oct 19, 2023 at 02:40:21PM +0000, Sebastian Ene wrote:
> Hi,
> 
> This can be used as a debugging tool for dumping the second stage
> page-tables under debugfs.
> 
> From the previous feedback I re-worked the series and added support for
> guest page-tables dumping under VHE & nVHE configuration. I extended the
> list of reviewers as I missed the interested parties in the first round. 
> 
> When CONFIG_NVHE_EL2_PTDUMP_DEBUGFS is enabled under pKVM environment,
> ptdump registers the 'host_stage2_kernel_page_tables' entry with debugfs.
> Guests are registering a file named '%u_guest_stage2_page_tables' when
> they are created. 

I believe guests entries should be also available for nVHE and VHE.

> 
> This allows us to dump the host stage-2 page-tables with the following command:
> cat /sys/kernel/debug/host_stage2_kernel_page_tables.

As it needs the debugfs anyway, this should probably live in the kvm/ debugfs
folder, while the VMs ptdump should be placed in their respective folder.

This is quite easy, you should get access to the global kvm_debugfs_dir and
struct kvm->debugfs_dentry.

> 
> The output is showing the entries in the following format:
> <IPA range> <size> <descriptor type> <access permissions> <mem_attributes>
> 
> The tool interprets the pKVM ownership annotation stored in the invalid
> entries and dumps to the console the ownership information. To be able
> to access the host stage-2 page-tables from the kernel, a new hypervisor
> call was introduced which allows us to snapshot the page-tables in a host
> provided buffer. The hypervisor call is hidden behind CONFIG_NVHE_EL2_DEBUG
> as this should be used under debugging environment.
> 
> Link to the first version:
> https://lore.kernel.org/all/20230927112517.2631674-1-sebastianene@google.com/
> 
> Changelog:
>   v1 -> v2:
>   * use the stage-2 pagetable walker for dumping descriptors instead of
>     the one provided by ptdump.
> 
>   * support for guests pagetables dumping under VHE/nVHE non-protected
> 
> Thanks,
> 
> 
> Sebastian Ene (11):
>   KVM: arm64: Add snap shooting the host stage-2 pagetables
>   arm64: ptdump: Use the mask from the state structure
>   arm64: ptdump: Add the walker function to the ptdump info structure
>   KVM: arm64: Move pagetable definitions to common header
>   arm64: ptdump: Introduce stage-2 pagetables format description
>   arm64: ptdump: Add hooks on debugfs file operations
>   arm64: ptdump: Register a debugfs entry for the host stage-2
>     page-tables
>   arm64: ptdump: Parse the host stage-2 page-tables from the snapshot
>   arm64: ptdump: Interpret memory attributes based on runtime
>     configuration
>   arm64: ptdump: Interpret pKVM ownership annotations
>   arm64: ptdump: Add support for guest stage-2 pagetables dumping
> 
>  arch/arm64/include/asm/kvm_asm.h              |   1 +
>  arch/arm64/include/asm/kvm_pgtable.h          |  85 +++
>  arch/arm64/include/asm/ptdump.h               |  27 +-
>  arch/arm64/kvm/Kconfig                        |  12 +
>  arch/arm64/kvm/hyp/include/nvhe/mem_protect.h |   8 +-
>  arch/arm64/kvm/hyp/nvhe/hyp-main.c            |  18 +
>  arch/arm64/kvm/hyp/nvhe/mem_protect.c         | 103 ++++
>  arch/arm64/kvm/hyp/pgtable.c                  |  98 ++--
>  arch/arm64/kvm/mmu.c                          |   3 +
>  arch/arm64/mm/ptdump.c                        | 487 +++++++++++++++++-
>  arch/arm64/mm/ptdump_debugfs.c                |  42 +-
>  11 files changed, 822 insertions(+), 62 deletions(-)
> 
> -- 
> 2.42.0.655.g421f12c284-goog
>