[RFC][PATCH 06/34] x86/boot: Use consistent value for iomem_resource.end

[Dave Hansen]

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

The 'struct cpuinfo_x86' values (including 'boot_cpu_info') get
written and overwritten rather randomly.  They are not stable
during early boot and readers end up getting a random mishmash
of hard-coded defaults or CPUID-provided values based on when
the values are read.

iomem_resource.end is one of these users.  Because of where it
is called, it ended up seeing .x86_phys_bits==MAX_PHYSMEM_BITS
which is (mostly) a compile-time default.  But
iomem_resource.end is never updated if the runtime CPUID
x86_phys_bits is lower.

Set iomem_resource.end to the compile-time value explicitly.
It does not need to be precise as this is mostly to ensure
that insane values can't be reserved in 'iomem_resource'.

Make MAX_PHYSMEM_BITS available outside of sparsemem
configurations by removing the #ifdef CONFIG_SPARSEMEM in the
header.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
---

 b/arch/x86/include/asm/sparsemem.h |    3 ---
 b/arch/x86/kernel/setup.c          |   10 +++++++++-
 2 files changed, 9 insertions(+), 4 deletions(-)

diff -puN arch/x86/kernel/setup.c~iomem_resource_end arch/x86/kernel/setup.c
--- a/arch/x86/kernel/setup.c~iomem_resource_end	2024-02-22 10:08:51.048554948 -0800
+++ b/arch/x86/kernel/setup.c	2024-02-22 10:21:04.485531464 -0800
@@ -51,6 +51,7 @@
 #include <asm/pci-direct.h>
 #include <asm/prom.h>
 #include <asm/proto.h>
+#include <asm/sparsemem.h>
 #include <asm/thermal.h>
 #include <asm/unwind.h>
 #include <asm/vsyscall.h>
@@ -813,7 +814,14 @@ void __init setup_arch(char **cmdline_p)
 	 */
 	early_reserve_memory();
 
-	iomem_resource.end = (1ULL << x86_phys_bits()) - 1;
+	/*
+	 * This was too big before.  It ended up getting MAX_PHYSMEM_BITS
+	 * even if .x86_phys_bits was eventually lowered below that.
+	 * But that was evidently harmless, so leave it too big, but
+	 * set it explicitly to MAX_PHYSMEM_BITS instead of taking a
+	 * trip through .x86_phys_bits.
+	 */
+	iomem_resource.end = (1ULL << MAX_PHYSMEM_BITS) - 1;
 	e820__memory_setup();
 	parse_setup_data();
 
diff -puN arch/x86/include/asm/sparsemem.h~iomem_resource_end arch/x86/include/asm/sparsemem.h
--- a/arch/x86/include/asm/sparsemem.h~iomem_resource_end	2024-02-22 10:19:56.842831828 -0800
+++ b/arch/x86/include/asm/sparsemem.h	2024-02-22 10:20:21.207804806 -0800
@@ -4,7 +4,6 @@
 
 #include <linux/types.h>
 
-#ifdef CONFIG_SPARSEMEM
 /*
  * generic non-linear memory support:
  *
@@ -29,8 +28,6 @@
 # define MAX_PHYSMEM_BITS	(pgtable_l5_enabled() ? 52 : 46)
 #endif
 
-#endif /* CONFIG_SPARSEMEM */
-
 #ifndef __ASSEMBLY__
 #ifdef CONFIG_NUMA_KEEP_MEMINFO
 extern int phys_to_target_node(phys_addr_t start);
_