Re: [PATCH v6 27/43] hw/cxl/host: Add support for CXL Fixed Memory Windows.

[Markus Armbruster <armbru@redhat.com>]

Jonathan Cameron via <qemu-devel@nongnu.org> writes:

> From: Jonathan Cameron <jonathan.cameron@huawei.com>
>
> The concept of these is introduced in [1] in terms of the
> description the CEDT ACPI table. The principal is more general.
> Unlike once traffic hits the CXL root bridges, the host system
> memory address routing is implementation defined and effectively
> static once observable by standard / generic system software.
> Each CXL Fixed Memory Windows (CFMW) is a region of PA space
> which has fixed system dependent routing configured so that
> accesses can be routed to the CXL devices below a set of target
> root bridges. The accesses may be interleaved across multiple
> root bridges.
>
> For QEMU we could have fully specified these regions in terms
> of a base PA + size, but as the absolute address does not matter
> it is simpler to let individual platforms place the memory regions.
>
> ExampleS:
> -cxl-fixed-memory-window targets=cxl.0,size=128G
> -cxl-fixed-memory-window targets=cxl.1,size=128G
> -cxl-fixed-memory-window targets=cxl0,targets=cxl.1,size=256G,interleave-granularity=2k
>
> Specifies
> * 2x 128G regions not interleaved across root bridges, one for each of
>   the root bridges with ids cxl.0 and cxl.1
> * 256G region interleaved across root bridges with ids cxl.0 and cxl.1
> with a 2k interleave granularity.
>
> When system software enumerates the devices below a given root bridge
> it can then decide which CFMW to use. If non interleave is desired
> (or possible) it can use the appropriate CFMW for the root bridge in
> question.  If there are suitable devices to interleave across the
> two root bridges then it may use the 3rd CFMS.
>
> A number of other designs were considered but the following constraints
> made it hard to adapt existing QEMU approaches to this particular problem.
> 1) The size must be known before a specific architecture / board brings
>    up it's PA memory map.  We need to set up an appropriate region.
> 2) Using links to the host bridges provides a clean command line interface
>    but these links cannot be established until command line devices have
>    been added.
>
> Hence the two step process used here of first establishing the size,
> interleave-ways and granularity + caching the ids of the host bridges
> and then, once available finding the actual host bridges so they can
> be used later to support interleave decoding.
>
> [1] CXL 2.0 ECN: CEDT CFMWS & QTG DSM (computeexpresslink.org / specifications)
>
> Signed-off-by: Jonathan Cameron <jonathan.cameron@huawei.com>

[...]

> diff --git a/hw/cxl/cxl-host.c b/hw/cxl/cxl-host.c
> new file mode 100644
> index 0000000000..9f303e6d8e
> --- /dev/null
> +++ b/hw/cxl/cxl-host.c

[...]

> +QemuOptsList qemu_cxl_fixed_window_opts = {
> +    .name = "cxl-fixed-memory-window",
> +    .implied_opt_name = "type",
> +    .head = QTAILQ_HEAD_INITIALIZER(qemu_cxl_fixed_window_opts.head),
> +    .desc = { { 0 } }
> +};
> +

[...]

> +static int parse_cxl_fixed_memory_window(void *opaque, QemuOpts *opts,
> +                                         Error **errp)
> +{
> +    CXLFixedMemoryWindowOptions *object = NULL;
> +    MachineState *ms = MACHINE(opaque);
> +    Error *err = NULL;
> +    Visitor *v = opts_visitor_new(opts);
> +
> +    visit_type_CXLFixedMemoryWindowOptions(v, NULL, &object, errp);
> +    visit_free(v);
> +    if (!object) {
> +        return -1;
> +    }
> +
> +    set_cxl_fixed_memory_window_options(ms, object, &err);
> +
> +    qapi_free_CXLFixedMemoryWindowOptions(object);
> +    if (err) {
> +        error_propagate(errp, err);
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
> +void parse_cxl_fixed_memory_window_opts(MachineState *ms)
> +{
> +    qemu_opts_foreach(qemu_find_opts("cxl-fixed-memory-window"),
> +                      parse_cxl_fixed_memory_window, ms, &error_fatal);
> +}

[...]

> diff --git a/qapi/machine.json b/qapi/machine.json
> index 42fc68403d..0998a9128d 100644
> --- a/qapi/machine.json
> +++ b/qapi/machine.json
> @@ -504,6 +504,21 @@
>     'dst': 'uint16',
>     'val': 'uint8' }}
>  
> +##
> +# @CXLFixedMemoryWindowOptions:
> +#
> +# Create a CXL Fixed Memory Window (for OptsVisitor)
> +#
> +# @targets: Target root bridge IDs

Missing: @size, @targets.

> +#
> +# Since X.X //fixme

Well, "fix me, please".

> +##
> +{ 'struct': 'CXLFixedMemoryWindowOptions',
> +  'data': {
> +      'size': 'size',
> +      '*interleave-granularity': 'size',
> +      'targets': ['str'] }}
> +
>  ##
>  # @X86CPURegister32:
>  #

[...]

> diff --git a/qemu-options.hx b/qemu-options.hx
> index ba3ae6a42a..b4d2cc6f48 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -467,6 +467,43 @@ SRST
>          -numa hmat-cache,node-id=1,size=10K,level=1,associativity=direct,policy=write-back,line=8
>  ERST
>  
> +DEF("cxl-fixed-memory-window", HAS_ARG, QEMU_OPTION_cxl_fixed_memory_window,
> +    "-cxl-fixed-memory-window targets=firsttarget,targets=secondtarget,size=size[,interleave-granularity=granularity]\n",
> +    QEMU_ARCH_ALL)
> +SRST
> +``-cxl-fixed-memory-window targets=firsttarget,targets=secondtarget,size=size[,interleave-granularity=granularity]``
> +    Define a CXL Fixed Memory Window (CFMW).
> +
> +    Described in the CXL 2.0 ECN: CEDT CFMWS & QTG _DSM.
> +
> +    They are regions of Host Physical Addresses (HPA) on a system which
> +    may be interleaved across one or more CXL host bridges.  The system
> +    software will assign particular devices into these windows and
> +    configure the downstream Host-managed Device Memory (HDM) decoders
> +    in root ports, switch ports and devices appropriately to meet the
> +    interleave requirements before enabling the memory devices.
> +
> +    ``targets=firsttarget`` provides the mapping to CXL host bridges
> +    which may be identified by the id provied in the -device entry.
> +    Multiple entries are needed to specify all the targets when
> +    the fixed memory window represents interleaved memory.
> +
> +    ``size=size`` sets the size of the CFMW. This must be a multiple of
> +    256MiB. The region will be aligned to 256MiB but the location is
> +    platform and configuration dependent.
> +
> +    ``interleave-granularity=granularity`` sets the granularity of
> +    interleave. Default 256KiB. Only 256KiB, 512KiB, 1024KiB, 2048KiB
> +    4096KiB, 8192KiB and 16384KiB granularities supported.
> +
> +    Example:
> +
> +    ::
> +
> +        -cxl-fixed-memory-window -targets=cxl.0,-targets=cxl.1,size=128G,interleave-granularity=512k
> +
> +ERST
> +
>  DEF("add-fd", HAS_ARG, QEMU_OPTION_add_fd,
>      "-add-fd fd=fd,set=set[,opaque=opaque]\n"
>      "                Add 'fd' to fd 'set'\n", QEMU_ARCH_ALL)
> diff --git a/softmmu/vl.c b/softmmu/vl.c
> index 5e1b35ba48..f83f158fff 100644
> --- a/softmmu/vl.c
> +++ b/softmmu/vl.c
> @@ -91,6 +91,7 @@
>  #include "qemu/config-file.h"
>  #include "qemu/qemu-options.h"
>  #include "qemu/main-loop.h"
> +#include "hw/cxl/cxl.h"
>  #ifdef CONFIG_VIRTFS
>  #include "fsdev/qemu-fsdev.h"
>  #endif
> @@ -2744,6 +2745,7 @@ void qmp_x_exit_preconfig(Error **errp)
>  
>      qemu_init_board();
>      qemu_create_cli_devices();
> +    cxl_fixed_memory_window_link_targets(errp);
>      qemu_machine_creation_done();
>  
>      if (loadvm) {
> @@ -2805,6 +2807,7 @@ void qemu_init(int argc, char **argv, char **envp)
>      qemu_add_opts(&qemu_msg_opts);
>      qemu_add_opts(&qemu_name_opts);
>      qemu_add_opts(&qemu_numa_opts);
> +    qemu_add_opts(&qemu_cxl_fixed_window_opts);
>      qemu_add_opts(&qemu_icount_opts);
>      qemu_add_opts(&qemu_semihosting_config_opts);
>      qemu_add_opts(&qemu_fw_cfg_opts);
> @@ -2927,6 +2930,13 @@ void qemu_init(int argc, char **argv, char **envp)
>                      exit(1);
>                  }
>                  break;
> +            case QEMU_OPTION_cxl_fixed_memory_window:
> +                opts = qemu_opts_parse_noisily(qemu_find_opts("cxl-fixed-memory-window"),
> +                                               optarg, true);
> +                if (!opts) {
> +                    exit(1);
> +                }
> +                break;
>              case QEMU_OPTION_display:
>                  parse_display(optarg);
>                  break;
> @@ -3764,6 +3774,7 @@ void qemu_init(int argc, char **argv, char **envp)
>  
>      qemu_resolve_machine_memdev();
>      parse_numa_opts(current_machine);
> +    parse_cxl_fixed_memory_window_opts(current_machine);
>  
>      if (vmstate_dump_file) {
>          /* dump and exit */

Have you considered using qobject_input_visitor_new_str() instead of
QemuOpts?