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

Vincent Donnefort
2023-10-20T08:19:44Z

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
>