Re: [PATCH v4 12/13] monitor: add 'info ramblock-attributes' command

[Peter Xu <peterx@redhat.com>]

On Mon, May 04, 2026 at 04:30:18PM +0400, Marc-André Lureau wrote:
> Add a new 'info ramblock-attributes' HMP command and the corresponding
> 'x-query-ramblock-attributes' QMP command to display the shared/private
> memory attributes for ram blocks.
> 
> The QMP command returns structured data (RamBlockAttributesInfo list
> with per-range shared/populated attributes), while HMP formats it for
> human consumption.
> 
> This is useful for debugging confidential guests (TDX, SNP) to inspect
> which memory regions are shared vs private, and their population state
> when a RamDiscardManager is present (e.g. virtio-mem).
> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>

Nobody is copied on this patch..  Let me add Markus and Dave at minimum..

Only one trivial question below:

> ---
>  qapi/machine.json             | 55 +++++++++++++++++++++++++++++++++
>  include/monitor/hmp.h         |  1 +
>  hw/core/machine-hmp-cmds.c    | 32 +++++++++++++++++++
>  system/ram-block-attributes.c | 72 +++++++++++++++++++++++++++++++++++++++++++
>  hmp-commands-info.hx          | 13 ++++++++
>  5 files changed, 173 insertions(+)
> 
> diff --git a/qapi/machine.json b/qapi/machine.json
> index 685e4e29b87..aac8a235cf6 100644
> --- a/qapi/machine.json
> +++ b/qapi/machine.json
> @@ -1738,6 +1738,61 @@
>    'returns': 'HumanReadableText',
>    'features': [ 'unstable' ] }
>  
> +##
> +# @RamBlockAttributeRange:
> +#
> +# A contiguous range within a ram block with uniform attributes.
> +#
> +# @start: start offset in bytes within the ram block
> +#
> +# @length: length in bytes of the range
> +#
> +# @shared: true if the range is shared, false if private
> +#
> +# @populated: true if the range is populated (only present when a
> +#     RamDiscardManager is managing the block)
> +#
> +# Since: 11.1
> +##
> +{ 'struct': 'RamBlockAttributeRange',
> +  'data': { 'start': 'uint64',
> +            'length': 'uint64',
> +            'shared': 'bool',
> +            '*populated': 'bool' } }
> +
> +##
> +# @RamBlockAttributesInfo:
> +#
> +# Shared/private memory attributes for a ram block.
> +#
> +# @name: the ram block identifier
> +#
> +# @ranges: list of attribute ranges
> +#
> +# Since: 11.1
> +##
> +{ 'struct': 'RamBlockAttributesInfo',
> +  'data': { 'name': 'str',
> +            'ranges': [ 'RamBlockAttributeRange' ] } }
> +
> +##
> +# @x-query-ramblock-attributes:
> +#
> +# Query ram block shared/private attributes.  This is useful
> +# to debug confidential guests.
> +#
> +# Features:
> +#
> +# @unstable: This command is meant for debugging.
> +#
> +# Returns: list of ram block attributes
> +#
> +# Since: 11.1
> +##
> +{ 'command': 'x-query-ramblock-attributes',
> +  'returns': [ 'RamBlockAttributesInfo' ],
> +  'features': [ 'unstable' ] }
> +
>  ##
>  # @x-query-roms:
>  #
> diff --git a/include/monitor/hmp.h b/include/monitor/hmp.h
> index e222bea60cd..4493952b417 100644
> --- a/include/monitor/hmp.h
> +++ b/include/monitor/hmp.h
> @@ -143,6 +143,7 @@ void hmp_info_dump(Monitor *mon, const QDict *qdict);
>  void hmp_hotpluggable_cpus(Monitor *mon, const QDict *qdict);
>  void hmp_info_vm_generation_id(Monitor *mon, const QDict *qdict);
>  void hmp_info_memory_size_summary(Monitor *mon, const QDict *qdict);
> +void hmp_info_ramblock_attributes(Monitor *mon, const QDict *qdict);
>  void hmp_info_replay(Monitor *mon, const QDict *qdict);
>  void hmp_replay_break(Monitor *mon, const QDict *qdict);
>  void hmp_replay_delete_break(Monitor *mon, const QDict *qdict);
> diff --git a/hw/core/machine-hmp-cmds.c b/hw/core/machine-hmp-cmds.c
> index 46846f741a2..122e1a0f735 100644
> --- a/hw/core/machine-hmp-cmds.c
> +++ b/hw/core/machine-hmp-cmds.c
> @@ -24,6 +24,7 @@
>  #include "qapi/string-output-visitor.h"
>  #include "qemu/error-report.h"
>  #include "system/numa.h"
> +#include "system/ramblock.h"
>  #include "hw/core/boards.h"
>  
>  void hmp_info_cpus(Monitor *mon, const QDict *qdict)
> @@ -388,3 +389,34 @@ void hmp_info_memory_size_summary(Monitor *mon, const QDict *qdict)
>      }
>      hmp_handle_error(mon, err);
>  }
> +
> +void hmp_info_ramblock_attributes(Monitor *mon, const QDict *qdict)
> +{
> +    Error *err = NULL;
> +    g_autoptr(RamBlockAttributesInfoList) list = NULL;
> +    RamBlockAttributesInfoList *it;
> +
> +    list = qmp_x_query_ramblock_attributes(&err);
> +    if (hmp_handle_error(mon, err)) {
> +        return;
> +    }
> +
> +    for (it = list; it; it = it->next) {
> +        RamBlockAttributesInfo *rba = it->value;
> +        RamBlockAttributeRangeList *r;
> +
> +        monitor_printf(mon, "%s:\n", rba->name);
> +        for (r = rba->ranges; r; r = r->next) {
> +            RamBlockAttributeRange *range = r->value;
> +            const char *shared = range->shared ? "shared" : "private";
> +            const char *pop = range->has_populated ?
> +                (range->populated ? "+populated" : "-populated") : "";
> +
> +            monitor_printf(mon,
> +                           "  0x%016" PRIx64 "-0x%016" PRIx64 " %s%s\n",
> +                           range->start,
> +                           range->start + range->length - 1,
> +                           shared, pop);
> +        }
> +    }
> +}
> diff --git a/system/ram-block-attributes.c b/system/ram-block-attributes.c
> index 59ec7a28eb0..f9573801b60 100644
> --- a/system/ram-block-attributes.c
> +++ b/system/ram-block-attributes.c
> @@ -11,6 +11,7 @@
>  
>  #include "qemu/osdep.h"
>  #include "qemu/error-report.h"
> +#include "qapi/qapi-commands-machine.h"
>  #include "system/ramblock.h"
>  #include "trace.h"
>  
> @@ -221,3 +222,74 @@ static void ram_block_attributes_class_init(ObjectClass *klass,
>      rdsc->get_min_granularity = ram_block_attributes_rds_get_min_granularity;
>      rdsc->is_populated = ram_block_attributes_rds_is_populated;
>  }
> +
> +RamBlockAttributesInfoList *qmp_x_query_ramblock_attributes(Error **errp)
> +{
> +    RamBlockAttributesInfoList *head = NULL, **tail = &head;
> +    RAMBlock *block;
> +    size_t rba_block_size = ram_block_attributes_get_block_size();
> +
> +    RCU_READ_LOCK_GUARD();
> +
> +    RAMBLOCK_FOREACH(block) {
> +        RamBlockAttributesInfo *rba;
> +        RamBlockAttributeRangeList **range_tail;
> +        RamBlockAttributes *attr = block->attributes;
> +        RamDiscardManager *rdm;
> +        bool has_rdm;
> +        unsigned long pos;
> +
> +        if (!attr) {
> +            continue;
> +        }
> +
> +        rdm = memory_region_get_ram_discard_manager(block->mr);
> +        has_rdm = rdm != NULL;
> +
> +        rba = g_new0(RamBlockAttributesInfo, 1);
> +        rba->name = g_strdup(block->idstr);
> +        range_tail = &rba->ranges;
> +
> +        pos = 0;
> +        while (pos < attr->bitmap_size) {
> +            bool is_shared = test_bit(pos, attr->bitmap);
> +            unsigned long next;
> +            uint64_t start_offset, length;
> +            RamBlockAttributeRange *range;
> +
> +            if (is_shared) {
> +                next = find_next_zero_bit(attr->bitmap,
> +                                          attr->bitmap_size, pos);
> +            } else {
> +                next = find_next_bit(attr->bitmap,
> +                                     attr->bitmap_size, pos);
> +            }
> +
> +            start_offset = (uint64_t)pos * rba_block_size;
> +            length = (uint64_t)(next - pos) * rba_block_size;
> +
> +            range = g_new0(RamBlockAttributeRange, 1);
> +            range->start = start_offset;
> +            range->length = length;
> +            range->shared = is_shared;
> +
> +            if (has_rdm) {

Is this only for extra safety?  My understanding is when reaching here,
attr!=NULL, which means we have at least one disgard manager source, then
the manager must be there.  So I wonder if we could assert.  But not a big
deal. Maybe I overlooked that it is needed?

> +                MemoryRegionSection section = {
> +                    .mr = block->mr,
> +                    .offset_within_region = start_offset,
> +                    .size = int128_make64(length),
> +                };
> +                range->has_populated = true;
> +                range->populated =
> +                    ram_discard_manager_is_populated(rdm, &section);
> +            }
> +
> +            QAPI_LIST_APPEND(range_tail, range);
> +            pos = next;
> +        }
> +
> +        QAPI_LIST_APPEND(tail, rba);
> +    }
> +
> +    return head;
> +}
> diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx
> index 74c741f80e2..1168b4c20ca 100644
> --- a/hmp-commands-info.hx
> +++ b/hmp-commands-info.hx
> @@ -774,6 +774,19 @@ SRST
>      Dump all the ramblocks of the system.
>  ERST
>  
> +    {
> +        .name       = "ramblock-attributes",
> +        .args_type  = "",
> +        .params     = "",
> +        .help       = "Display ramblock shared/private attributes",
> +        .cmd        = hmp_info_ramblock_attributes,
> +    },
> +
> +SRST
> +  ``info ramblock-attributes``
> +    Display the shared/private memory attributes for ram blocks.
> +ERST
> +
>      {
>          .name       = "hotpluggable-cpus",
>          .args_type  = "",
> 
> -- 
> 2.54.0
> 
> 

-- 
Peter Xu