Re: [PATCH] perf/x86/intel/uncore: Fix a kernel WARNING triggered by maxcpus=1

[John Donnelly <John.p.donnelly@oracle.com>]

On 5/26/21 8:58 AM, kan.liang@linux.intel.com wrote:
> From: Kan Liang <kan.liang@linux.intel.com>
> 
> A kernel WARNING may be triggered when setting maxcpus=1.
> 
> The uncore counters are Die-scope. When probing a PCI device, only the
> BUS information can be retrieved. The uncore driver has to maintain a
> mapping table used to calculate the logical Die ID from a given BUS#.
> 
> Before the patch ba9506be4e40, the mapping table stores the mapping
> information from the BUS# -> a Physical Socket ID. To calculate the
> logical die ID, perf does,
> - In snbep_pci2phy_map_init(), retrieve the BUS# -> a Physical Socket ID
>    from the UBOX PCI configure space.
> - Calculate the mapping information (a BUS# -> a Physical Socket ID) for
>    the other PCI BUS.
> - In the uncore_pci_probe(), get the physical Socket ID from a given BUS
>    and the mapping table.
> - Calculate the logical Die ID
> 
> Since only the logical Die ID is required, with the patch ba9506be4e40,
> the mapping table stores the mapping information from the BUS# -> a
> logical Die ID. Now perf does,
> - In snbep_pci2phy_map_init(), retrieve the BUS# -> a Physical Socket ID
>    from the UBOX PCI configure space.
> - Calculate the logical Die ID
> - Calculate the mapping information (a BUS# -> a logical Die ID) for the
>    other PCI BUS.
> - In the uncore_pci_probe(), get the logical die ID from a given BUS and
>    the mapping table.
> 
> When calculating the logical Die ID, -1 may be returned, especially when
> maxcpus=1. Here, -1 means the logical Die ID is not found. But when
> calculating the mapping information for the other PCI BUS, -1 indicates
> that it's the other PCI BUS that requires the calculation of the
> mapping. The driver will mistakenly do the calculation.
> 
> Uses the -ENODEV to indicate the case which the logical Die ID is not
> found. The driver will not mess up the mapping table anymore.
> 
> Fixes: ba9506be4e40 ("perf/x86/intel/uncore: Store the logical die id
> instead of the physical die id.")
> Reported-by: John Donnelly <john.p.donnelly@oracle.com>
> Tested-by: John Donnelly <john.p.donnelly@oracle.com>
> Signed-off-by: Kan Liang <kan.liang@linux.intel.com>

Acked-by: John Donnelly <john.p.donnelly@oracle.com>
> ---
>   arch/x86/events/intel/uncore_snbep.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/events/intel/uncore_snbep.c b/arch/x86/events/intel/uncore_snbep.c
> index f57d9cb..035787c 100644
> --- a/arch/x86/events/intel/uncore_snbep.c
> +++ b/arch/x86/events/intel/uncore_snbep.c
> @@ -1413,6 +1413,8 @@ static int snbep_pci2phy_map_init(int devid, int nodeid_loc, int idmap_loc, bool
>   						die_id = i;
>   					else
>   						die_id = topology_phys_to_logical_pkg(i);
> +					if (die_id < 0)
> +						die_id = -ENODEV;
>   					map->pbus_to_dieid[bus] = die_id;
>   					break;
>   				}
> @@ -1459,14 +1461,14 @@ static int snbep_pci2phy_map_init(int devid, int nodeid_loc, int idmap_loc, bool
>   			i = -1;
>   			if (reverse) {
>   				for (bus = 255; bus >= 0; bus--) {
> -					if (map->pbus_to_dieid[bus] >= 0)
> +					if (map->pbus_to_dieid[bus] != -1)
>   						i = map->pbus_to_dieid[bus];
>   					else
>   						map->pbus_to_dieid[bus] = i;
>   				}
>   			} else {
>   				for (bus = 0; bus <= 255; bus++) {
> -					if (map->pbus_to_dieid[bus] >= 0)
> +					if (map->pbus_to_dieid[bus] != -1)
>   						i = map->pbus_to_dieid[bus];
>   					else
>   						map->pbus_to_dieid[bus] = i;
>