Re: [PATCH v3 1/6] Add an "info pg" command that prints the current page tables

["Daniel P. Berrangé" <berrange@redhat.com>]

On Thu, Jun 06, 2024 at 10:02:48AM -0400, Don Porter wrote:
> The new "info pg" monitor command prints the current page table,
> including virtual address ranges, flag bits, and snippets of physical
> page numbers.  Completely filled regions of the page table with
> compatible flags are "folded", with the result that the complete
> output for a freshly booted x86-64 Linux VM can fit in a single
> terminal window.  The output looks like this:
> 
> VPN range             Entry         Flags            Physical page
> [7f0000000-7f0000000] PML4[0fe]     ---DA--UWP
>   [7f28c0000-7f28fffff]  PDP[0a3]     ---DA--UWP
>     [7f28c4600-7f28c47ff]  PDE[023]     ---DA--UWP
>       [7f28c4655-7f28c4656]  PTE[055-056] X--D---U-P 0000007f14-0000007f15
>       [7f28c465b-7f28c465b]  PTE[05b]     ----A--U-P 0000001cfc
> ...
> [ff8000000-ff8000000] PML4[1ff]     ---DA--UWP
>   [ffff80000-ffffbffff]  PDP[1fe]     ---DA---WP
>     [ffff81000-ffff81dff]  PDE[008-00e] -GSDA---WP 0000001000-0000001dff
>   [ffffc0000-fffffffff]  PDP[1ff]     ---DA--UWP
>     [ffffff400-ffffff5ff]  PDE[1fa]     ---DA--UWP
>       [ffffff5fb-ffffff5fc]  PTE[1fb-1fc] XG-DACT-WP 00000fec00 00000fee00
>     [ffffff600-ffffff7ff]  PDE[1fb]     ---DA--UWP
>       [ffffff600-ffffff600]  PTE[000]     -G-DA--U-P 0000001467
> 
> This draws heavy inspiration from Austin Clements' original patch.
> 
> This also adds a generic page table walker, which other monitor
> and execution commands will be migrated to in subsequent patches.
> 
> Signed-off-by: Don Porter <porter@cs.unc.edu>
> ---
>  hmp-commands-info.hx              |  13 ++
>  hw/core/cpu-sysemu.c              | 140 ++++++++++++
>  include/hw/core/cpu.h             |  34 ++-
>  include/hw/core/sysemu-cpu-ops.h  | 156 +++++++++++++
>  include/monitor/hmp-target.h      |   1 +
>  monitor/hmp-cmds-target.c         | 198 +++++++++++++++++
>  target/i386/arch_memory_mapping.c | 351 +++++++++++++++++++++++++++++-
>  target/i386/cpu.c                 |  11 +
>  target/i386/cpu.h                 |  15 ++
>  target/i386/monitor.c             | 165 ++++++++++++++
>  10 files changed, 1082 insertions(+), 2 deletions(-)
> +
> +void hmp_info_pg(Monitor *mon, const QDict *qdict)
> +{
> +    struct mem_print_state state;
> +
> +    CPUState *cs = mon_get_cpu(mon);
> +    if (!cs) {
> +        monitor_printf(mon, "Unable to get CPUState.  Internal error\n");
> +        return;
> +    }
> +
> +    CPUClass *cc = CPU_GET_CLASS(cs);
> +
> +    if ((!cc->sysemu_ops->pte_child)
> +        || (!cc->sysemu_ops->pte_leaf)
> +        || (!cc->sysemu_ops->pte_leaf_page_size)
> +        || (!cc->sysemu_ops->page_table_entries_per_node)
> +        || (!cc->sysemu_ops->pte_flags)
> +        || (!cc->sysemu_ops->mon_init_page_table_iterator)
> +        || (!cc->sysemu_ops->mon_info_pg_print_header)
> +        || (!cc->sysemu_ops->mon_flush_page_print_state)) {
> +        monitor_printf(mon, "Info pg unsupported on this ISA\n");
> +        return;
> +    }
> +
> +    if (!cc->sysemu_ops->mon_init_page_table_iterator(mon, &state)) {
> +        monitor_printf(mon, "Unable to initialize page table iterator\n");
> +        return;
> +    }
> +
> +    state.flush_interior = true;
> +    state.require_physical_contiguity = true;
> +    state.flusher = cc->sysemu_ops->mon_flush_page_print_state;
> +
> +    cc->sysemu_ops->mon_info_pg_print_header(mon, &state);
> +
> +    /*
> +     * We must visit interior entries to get the hierarchy, but
> +     * can skip not present mappings
> +     */
> +    for_each_pte(cs, &compressing_iterator, &state, true, false);
> +
> +    /* Print last entry, if one present */
> +    cc->sysemu_ops->mon_flush_page_print_state(cs, &state);
> +}

Please don't add new HMP commands that don't have a QMP
equivalent.

This should be adding an 'x-query-pg' QMP command, which
returns HumanReadableText, and then call that from the HMP

There is guidance on this here:

  https://www.qemu.org/docs/master/devel/writing-monitor-commands.html#writing-a-debugging-aid-returning-unstructured-text

If you need more real examples, look at the various
'x-query-XXXX' commands in qapi/machine.json  and
their impl.


With regards,
Daniel
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