Re: [PATCH v3] hw/arm/virt-acpi-build: Fix id_count in build_iort_id_mapping

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jun 18, 2024 at 02:11:10PM -0700, Nicolin Chen wrote:
> It's observed that Linux kernel booting with the VM reports a "conflicting
> mapping for input ID" FW_BUG.
> 
> The IORT doc defines "Number of IDs" to be "the number of IDs in the range
> minus one", while virt-acpi-build.c simply stores the number of IDs in the
> id_count without the "minus one". Meanwhile, some of the callers pass in a
> 0xFFFF following the spec. So, this is a mismatch between the function and
> its callers.
> 
> Fix build_iort_id_mapping() by internally subtracting one from the pass-in
> @id_count. Accordingly make sure that all existing callers pass in a value
> without the "minus one", i.e. change all 0xFFFFs to 0x10000s.
> 
> Also, add a few lines of comments to highlight this change along with the
> referencing document for this build_iort_id_mapping().
> 
> Fixes: 42e0f050e3a5 ("hw/arm/virt-acpi-build: Add IORT support to bypass SMMUv3")
> Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> ---
> Changelog
> v3:
>  * Added "-1" internally in build_iort_id_mapping() instead
>  * Added comments to highlight this and referencing doc
> v2:
>  https://lore.kernel.org/all/20240617223945.906996-1-nicolinc@nvidia.com/
>  * Moved "-1" to the same line of id_count calculation
>  * Added "+1" to the next_range.input_base calculation
> v1:
>  https://lore.kernel.org/all/20240613234802.828265-1-nicolinc@nvidia.com/
> 
>  hw/arm/virt-acpi-build.c | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> index c3ccfef026..ee6f56b410 100644
> --- a/hw/arm/virt-acpi-build.c
> +++ b/hw/arm/virt-acpi-build.c
> @@ -209,12 +209,20 @@ static void acpi_dsdt_add_tpm(Aml *scope, VirtMachineState *vms)
>  #define ROOT_COMPLEX_ENTRY_SIZE 36
>  #define IORT_NODE_OFFSET 48
>  
> +/*
> + * Input Output Remapping Table (IORT) -- Table 4 ID mapping format
> + * Conforms to "IO Remapping Table System Software on ARM Platforms",
> + * Document number: ARM DEN 0049E.b, Feb 2021
> + *
> + * Note that @id_count will be internally subtracted by one, following
> + * the IORT spec.
> + */
>  static void build_iort_id_mapping(GArray *table_data, uint32_t input_base,
>                                    uint32_t id_count, uint32_t out_ref)
>  {
> -    /* Table 4 ID mapping format */
>      build_append_int_noprefix(table_data, input_base, 4); /* Input base */
> -    build_append_int_noprefix(table_data, id_count, 4); /* Number of IDs */
> +    /* Number of IDs - The number of IDs in the range minus one */
> +    build_append_int_noprefix(table_data, id_count - 1, 4);
>      build_append_int_noprefix(table_data, input_base, 4); /* Output base */
>      build_append_int_noprefix(table_data, out_ref, 4); /* Output Reference */
>      /* Flags */
> @@ -306,8 +314,8 @@ build_iort(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
>          }
>  
>          /* Append the last RC -> ITS ID mapping */
> -        if (next_range.input_base < 0xFFFF) {
> -            next_range.id_count = 0xFFFF - next_range.input_base;
> +        if (next_range.input_base < 0x10000) {
> +            next_range.id_count = 0x10000 - next_range.input_base;
>              g_array_append_val(its_idmaps, next_range);
>          }

A change of logic here - I think the new one is right and old
one was wrong, actually. Right?

>  
> @@ -366,7 +374,7 @@ build_iort(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
>          build_append_int_noprefix(table_data, 0, 4);
>  
>          /* output IORT node is the ITS group node (the first node) */
> -        build_iort_id_mapping(table_data, 0, 0xFFFF, IORT_NODE_OFFSET);
> +        build_iort_id_mapping(table_data, 0, 0x10000, IORT_NODE_OFFSET);
>      }
>  
>      /* Table 17 Root Complex Node */
> @@ -419,7 +427,7 @@ build_iort(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
>          }
>      } else {
>          /* output IORT node is the ITS group node (the first node) */
> -        build_iort_id_mapping(table_data, 0, 0xFFFF, IORT_NODE_OFFSET);
> +        build_iort_id_mapping(table_data, 0, 0x10000, IORT_NODE_OFFSET);
>      }
>  
>      acpi_table_end(linker, &table);
> -- 
> 2.43.0