Commit 78a509fba9c9 ("x86/boot: Ignore NMIs during very early boot") added
empty handler in early boot stage to avoid boot failure by spurious NMIs.
Add a diagnostic message in case we need to know whether early NMIs have
occurred and/or what happened to them.
Signed-off-by: Jun'ichi Nomura <[email protected]>
Suggested-by: Borislav Petkov <[email protected]>
Suggested-by: H. Peter Anvin <[email protected]>
Link: https://lore.kernel.org/lkml/20231130103339.GCZWhlA196uRklTMNF@fat_crate.local/
diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c
--- a/arch/x86/boot/compressed/ident_map_64.c
+++ b/arch/x86/boot/compressed/ident_map_64.c
@@ -387,7 +387,10 @@ void do_boot_page_fault(struct pt_regs *regs, unsigned long error_code)
kernel_add_identity_map(address, end);
}
+extern int spurious_nmi_count;
+
void do_boot_nmi_trap(struct pt_regs *regs, unsigned long error_code)
{
/* Empty handler to ignore NMI during early boot */
+ spurious_nmi_count++;
}
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -357,6 +357,8 @@ unsigned long decompress_kernel(unsigned char *outbuf, unsigned long virt_addr,
return entry;
}
+int spurious_nmi_count;
+
/*
* The compressed kernel image (ZO), has been moved so that its position
* is against the end of the buffer used to hold the uncompressed kernel
@@ -493,6 +495,12 @@ asmlinkage __visible void *extract_kernel(void *rmode, unsigned char *output)
/* Disable exception handling before booting the kernel */
cleanup_exception_handling();
+ if (spurious_nmi_count) {
+ error_putstr("Spurious early NMI ignored. Number of NMIs: 0x");
+ error_puthex(spurious_nmi_count);
+ error_putstr("\n");
+ }
+
return output + entry_offset;
}