Messages in this thread | | | Date | Wed, 22 Nov 2023 23:18:45 +0000 | From | Oliver Upton <> | Subject | Re: [PATCH v3 00/10] arm64: ptdump: View the second stage page-tables |
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Hi Seb,
On Wed, Nov 15, 2023 at 05:16:30PM +0000, Sebastian Ene wrote: > Hi, > > This can be used as a debugging tool for dumping the second stage > page-tables. > > When CONFIG_PTDUMP_STAGE2_DEBUGFS is enabled, ptdump registers > '/sys/debug/kvm/<guest_id>/stage2_page_tables' entry with debugfs > upon guest creation. This allows userspace tools (eg. cat) to dump the > stage-2 pagetables by reading the registered file. > > Reading the debugfs file shows stage-2 memory ranges in following format: > <IPA range> <size> <descriptor type> <access permissions> <mem_attributes> > > Under pKVM configuration(kvm-arm.mode=protected) ptdump registers an entry > for the host stage-2 pagetables in the following path: > /sys/debug/kvm/host_stage2_page_tables/ > > 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.
While I think the value of the feature you're proposing is great, I'm not a fan of the current shape of this series.
Reusing note_page() for the stage-2 dump is somewhat convenient, but the series pulls a **massive** amount of KVM details outside of KVM:
- Open-coding the whole snapshotting interface with EL2 outside of KVM. This is a complete non-starter for me; the kernel<->EL2 interface needs to be owned by the EL1 portions of KVM.
- Building page-table walkers using the KVM pgtable library outside of KVM.
- Copying (rather than directly calling) the logic responsible for things like FWB and PGD concatenation.
- Hoisting the definition of _software bits_ outside of KVM. I'm less concerned about hardware bits since they have an unambiguous meaning.
I think exporting the necessary stuff from ptdump into KVM will lead to a much cleaner implementation.
-- Thanks, Oliver
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