Re: [PATCH v10 12/30] x86/resctrl: Expand the width of domid by replacing mon_data_bits

[Reinette Chatre]

Hi James,

On 5/8/25 10:18 AM, James Morse wrote:
> MPAM platforms retrieve the cache-id property from the ACPI PPTT table.
> The cache-id field is 32 bits wide. Under resctrl, the cache-id becomes
> the domain-id, and is packed into the mon_data_bits union bitfield.
> The width of cache-id in this field is 14 bits.
> 
> Expanding the union would break 32bit x86 platforms as this union is
> stored as the kernfs kn->priv pointer. This saved allocating memory
> for the priv data storage.
> 
> The firmware on MPAM platforms have used the PPTT cache-id field to
> expose the interconnect's id for the cache, which is sparse and uses
> more than 14 bits. Use of this id is to enable PCIe direct cache
> injection hints. Using this feature with VFIO means the value provided
> by the ACPI table should be exposed to user-space.
> 
> To support cache-id values greater than 14 bits, convert the
> mon_data_bits union to a structure. These are shared between control
> and monitor groups, and are allocated on first use. The list of
> allocated struct mon_data is free'd when the filesystem is umount()ed.
> 
> Co-developed-by: Tony Luck <tony.luck@xxxxxxxxx>
> Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
> Signed-off-by: James Morse <james.morse@xxxxxxx>
> Tested-by: Babu Moger <babu.moger@xxxxxxx>
> Tested-by: Shaopeng Tan <tan.shaopeng@xxxxxxxxxxxxxx>
> ---

Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>

Reinette