x86/cpu: Provide a sane leaf 0xb/0x1f parser

detect_extended_topology() along with it's early() variant is a classic
example for duct tape engineering:

  - It evaluates an array of subleafs with a boatload of local variables
    for the relevant topology levels instead of using an array to save the
    enumerated information and propagate it to the right level

  - It has no boundary checks for subleafs

  - It prevents updating the die_id with a crude workaround instead of
    checking for leaf 0xb which does not provide die information.

  - It's broken vs. the number of dies evaluation as it uses:

      num_processors[DIE_LEVEL] / num_processors[CORE_LEVEL]

    which "works" only correctly if there is none of the intermediate
    topology levels (MODULE/TILE) enumerated.

There is zero value in trying to "fix" that code as the only proper fix is
to rewrite it from scratch.

Implement a sane parser with proper code documentation, which will be used
for the consolidated topology evaluation in the next step.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Juergen Gross <jgross@suse.com>
Tested-by: Sohil Mehta <sohil.mehta@intel.com>
Tested-by: Michael Kelley <mhklinux@outlook.com>
Tested-by: Zhang Rui <rui.zhang@intel.com>
Tested-by: Wang Wendy <wendy.wang@intel.com>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://lore.kernel.org/r/20240212153624.830571770@linutronix.de

1 files changed, 12 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/topology.h b/arch/x86/kernel/cpu/topology.h
index 934a100b9fe6..2b100cd11f17 100644
--- a/arch/x86/kernel/cpu/topology.h
+++ b/arch/x86/kernel/cpu/topology.h
@@ -16,6 +16,7 @@ void cpu_init_topology(struct cpuinfo_x86 *c);
 void cpu_parse_topology(struct cpuinfo_x86 *c);
 void topology_set_dom(struct topo_scan *tscan, enum x86_topology_domains dom,
 		      unsigned int shift, unsigned int ncpus);
+bool cpu_parse_topology_ext(struct topo_scan *tscan);
 
 static inline u32 topo_shift_apicid(u32 apicid, enum x86_topology_domains dom)
 {
@@ -36,4 +37,15 @@ static inline u32 topo_domain_mask(enum x86_topology_domains dom)
 	return (1U << x86_topo_system.dom_shifts[dom]) - 1;
 }
 
+/*
+ * Update a domain level after the fact without propagating. Used to fixup
+ * broken CPUID enumerations.
+ */
+static inline void topology_update_dom(struct topo_scan *tscan, enum x86_topology_domains dom,
+				       unsigned int shift, unsigned int ncpus)
+{
+	tscan->dom_shifts[dom] = shift;
+	tscan->dom_ncpus[dom] = ncpus;
+}
+
 #endif /* ARCH_X86_TOPOLOGY_H */