Patch "x86/boot: Ignore NMIs during very early boot" has been added to the 6.1-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    x86/boot: Ignore NMIs during very early boot

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-boot-ignore-nmis-during-very-early-boot.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 4bb36a11a1a1016fd8a42375099e9780bc5219f3
Author: Jun'ichi Nomura <junichi.nomura@xxxxxxx>
Date:   Wed Nov 29 15:44:49 2023 -0500

    x86/boot: Ignore NMIs during very early boot
    
    [ Upstream commit 78a509fba9c9b1fcb77f95b7c6be30da3d24823a ]
    
    When there are two racing NMIs on x86, the first NMI invokes NMI handler and
    the 2nd NMI is latched until IRET is executed.
    
    If panic on NMI and panic kexec are enabled, the first NMI triggers
    panic and starts booting the next kernel via kexec. Note that the 2nd
    NMI is still latched. During the early boot of the next kernel, once
    an IRET is executed as a result of a page fault, then the 2nd NMI is
    unlatched and invokes the NMI handler.
    
    However, NMI handler is not set up at the early stage of boot, which
    results in a boot failure.
    
    Avoid such problems by setting up a NOP handler for early NMIs.
    
    [ mingo: Refined the changelog. ]
    
    Signed-off-by: Jun'ichi Nomura <junichi.nomura@xxxxxxx>
    Signed-off-by: Derek Barbosa <debarbos@xxxxxxxxxx>
    Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
    Cc: Kees Cook <keescook@xxxxxxxxxxxx>
    Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
    Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
    Cc: Andy Lutomirski <luto@xxxxxxxxxx>
    Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
    Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c
index b4155273df89..d34222816c9f 100644
--- a/arch/x86/boot/compressed/ident_map_64.c
+++ b/arch/x86/boot/compressed/ident_map_64.c
@@ -393,3 +393,8 @@ void do_boot_page_fault(struct pt_regs *regs, unsigned long error_code)
 	 */
 	kernel_add_identity_map(address, end);
 }
+
+void do_boot_nmi_trap(struct pt_regs *regs, unsigned long error_code)
+{
+	/* Empty handler to ignore NMI during early boot */
+}
diff --git a/arch/x86/boot/compressed/idt_64.c b/arch/x86/boot/compressed/idt_64.c
index 3cdf94b41456..d100284bbef4 100644
--- a/arch/x86/boot/compressed/idt_64.c
+++ b/arch/x86/boot/compressed/idt_64.c
@@ -61,6 +61,7 @@ void load_stage2_idt(void)
 	boot_idt_desc.address = (unsigned long)boot_idt;
 
 	set_idt_entry(X86_TRAP_PF, boot_page_fault);
+	set_idt_entry(X86_TRAP_NMI, boot_nmi_trap);
 
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 	/*
diff --git a/arch/x86/boot/compressed/idt_handlers_64.S b/arch/x86/boot/compressed/idt_handlers_64.S
index 22890e199f5b..4d03c8562f63 100644
--- a/arch/x86/boot/compressed/idt_handlers_64.S
+++ b/arch/x86/boot/compressed/idt_handlers_64.S
@@ -70,6 +70,7 @@ SYM_FUNC_END(\name)
 	.code64
 
 EXCEPTION_HANDLER	boot_page_fault do_boot_page_fault error_code=1
+EXCEPTION_HANDLER	boot_nmi_trap do_boot_nmi_trap error_code=0
 
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 EXCEPTION_HANDLER	boot_stage1_vc do_vc_no_ghcb		error_code=1
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index 20118fb7c53b..a49d9219c06e 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -190,6 +190,7 @@ static inline void cleanup_exception_handling(void) { }
 
 /* IDT Entry Points */
 void boot_page_fault(void);
+void boot_nmi_trap(void);
 void boot_stage1_vc(void);
 void boot_stage2_vc(void);