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

Sebastian Ene
2023-10-23T14:32:44Z

On Fri, Oct 20, 2023 at 09:19:33AM +0100, Vincent Donnefort wrote:
> 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.

Hi,

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

Yes, we support dumping the guest stage-2 pagetables with this under
both modes. The host stage-2 is available only in
kvm.arm.mode="protected".

> >
> > 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.
>

Right, I was thinking to place them under kvm/ debugfs entry but then I
noticed that ptdump files are not registered under this path.

> >
> > 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
> >