[tip: x86/kdump] x86/crash: Reserve elfcorehdr for CONFIG_NR_CPUS, not CONFIG_NR_CPUS_DEFAULT

[tip-bot2 for Ionut Nechita]

The following commit has been merged into the x86/kdump branch of tip:

Commit-ID:     6664ad1026b558563702f9a1ce637df33e7c001e
Gitweb:        https://git.kernel.org/tip/6664ad1026b558563702f9a1ce637df33e7c001e
Author:        Ionut Nechita <ionut.nechita@xxxxxxxxxxxxx>
AuthorDate:    Tue, 01 Sep 2026 10:10:40 +03:00
Committer:     Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
CommitterDate: Wed, 02 Sep 2026 14:25:06 -07:00

x86/crash: Reserve elfcorehdr for CONFIG_NR_CPUS, not CONFIG_NR_CPUS_DEFAULT

NR_CPUS_DEFAULT is purely a Kconfig thing.  Its entire purpose in life is
to start NR_CPUS at a sane value.  There is precisely one (buggy)
reference to it outside of Kconfig in the whole kernel: the x86 crash
code.

That code undersizes the elfcorehdr reservation whenever NR_CPUS exceeds
NR_CPUS_DEFAULT, because the header carries one phdr per possible CPU and
num_possible_cpus() is bounded by NR_CPUS.  kexec_file_load(2) then fails
with -EINVAL from sanity_check_segment_list(), and kexec_load(2) silently
truncates the elfcorehdr, which surfaces later as a bad or unusable dump.

Size the elfcorehdr reservation with NR_CPUS instead.

Fixes: ea53ad9cf73b ("x86/crash: add x86 crash hotplug support")
Signed-off-by: Ionut Nechita <ionut.nechita@xxxxxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Reviewed-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
Reviewed-by: Bradley Morgan <brads@xxxxxxxxxxxxxx>
Reviewed-by: Sourabh Jain <sourabhjain@xxxxxxxxxxxxx>
Acked-by: Baoquan He <baoquan.he@xxxxxxxxx>
Link: https://patch.msgid.link/20260901071041.16311-2-ionut.nechita@xxxxxxxxxxxxx
---
 arch/x86/kernel/crash.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index e681ec9..e6f2393 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -369,9 +369,9 @@ int crash_load_segments(struct kimage *image)
 	 * maximum CPUs and maximum memory ranges.
 	 */
 	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
-		pnum = 2 + CONFIG_NR_CPUS_DEFAULT + CONFIG_CRASH_MAX_MEMORY_RANGES;
+		pnum = 2 + CONFIG_NR_CPUS + CONFIG_CRASH_MAX_MEMORY_RANGES;
 	else
-		pnum += 2 + CONFIG_NR_CPUS_DEFAULT;
+		pnum += 2 + CONFIG_NR_CPUS;
 
 	if (pnum < (unsigned long)PN_XNUM) {
 		kbuf.memsz = pnum * sizeof(Elf64_Phdr);
@@ -430,7 +430,7 @@ unsigned int arch_crash_get_elfcorehdr_size(void)
 	unsigned int sz;
 
 	/* kernel_map, VMCOREINFO and maximum CPUs */
-	sz = 2 + CONFIG_NR_CPUS_DEFAULT;
+	sz = 2 + CONFIG_NR_CPUS;
 	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
 		sz += CONFIG_CRASH_MAX_MEMORY_RANGES;
 	sz *= sizeof(Elf64_Phdr);