[tip: x86/boot] x86/boot: Add a message about ignored early NMIs

[tip-bot2 for NOMURA JUNICHI(野村 淳一) <tip-bot2@xxxxxxxxxxxxx>]

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

Commit-ID:     ac456ca0af4fe9630cf84e7efd20b7f7bf596aab
Gitweb:        https://git.kernel.org/tip/ac456ca0af4fe9630cf84e7efd20b7f7bf596aab
Author:        NOMURA JUNICHI(野村　淳一) <junichi.nomura@xxxxxxx>
AuthorDate:    Fri, 02 Feb 2024 03:51:58 
Committer:     Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Tue, 06 Feb 2024 10:51:11 +01:00

x86/boot: Add a message about ignored early NMIs

Commit

  78a509fba9c9 ("x86/boot: Ignore NMIs during very early boot")

added an empty handler in early boot stage to avoid boot failure due to
spurious NMIs.

Add a diagnostic message to show that early NMIs have occurred.

  [ bp: Touchups. ]

  [ Committer note: tested by stopping the guest really early and
    injecting NMIs through qemu's monitor. Result:

    early console in setup code
    Spurious early NMIs ignored: 13
    ... ]

Suggested-by: Borislav Petkov <bp@xxxxxxxxx>
Suggested-by: H. Peter Anvin <hpa@xxxxxxxxx>
Signed-off-by: Jun'ichi Nomura <junichi.nomura@xxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/lkml/20231130103339.GCZWhlA196uRklTMNF@fat_crate.local
---
 arch/x86/boot/compressed/ident_map_64.c | 2 +-
 arch/x86/boot/compressed/misc.c         | 7 +++++++
 arch/x86/boot/compressed/misc.h         | 1 +
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c
index d040080..4a029ba 100644
--- a/arch/x86/boot/compressed/ident_map_64.c
+++ b/arch/x86/boot/compressed/ident_map_64.c
@@ -389,5 +389,5 @@ void do_boot_page_fault(struct pt_regs *regs, unsigned long error_code)
 
 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
index bf2aac4..bd6857a 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -52,6 +52,7 @@ struct port_io_ops pio_ops;
 
 memptr free_mem_ptr;
 memptr free_mem_end_ptr;
+int spurious_nmi_count;
 
 static char *vidmem;
 static int vidport;
@@ -506,6 +507,12 @@ 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 NMIs ignored: ");
+		error_putdec(spurious_nmi_count);
+		error_putstr("\n");
+	}
+
 	return output + entry_offset;
 }
 
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index 6502bc6..b353a7b 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -59,6 +59,7 @@ extern char _head[], _end[];
 /* misc.c */
 extern memptr free_mem_ptr;
 extern memptr free_mem_end_ptr;
+extern int spurious_nmi_count;
 void *malloc(int size);
 void free(void *where);
 void __putstr(const char *s);