Commit d358b451 authored by David Woodhouse's avatar David Woodhouse Committed by Ingo Molnar
Browse files

x86/kexec: Add 8250 serial port output 



If a serial port was configured for early_printk, use it for debug output
from the relocate_kernel exception handler too.

Signed-off-by: default avatarDavid Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250326142404.256980-2-dwmw2@infradead.org
parent a23be6cc

arch/x86/include/asm/kexec.h

+1 −0
Original line number Diff line number Diff line
@@ -64,6 +64,7 @@ extern unsigned long kexec_pa_table_page; 
extern unsigned long kexec_pa_swap_page;

extern gate_desc kexec_debug_idt[];

extern unsigned char kexec_debug_exc_vectors[];

extern uint16_t kexec_debug_8250_port;

#endif



/*

arch/x86/kernel/early_printk.c

+6 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

#include <linux/console.h>

#include <linux/kernel.h>

#include <linux/kexec.h>

#include <linux/init.h>

#include <linux/string.h>

#include <linux/screen_info.h>
@@ -144,6 +145,11 @@ static __init void early_serial_hw_init(unsigned divisor) 
	static_call(serial_out)(early_serial_base, DLL, divisor & 0xff);

	static_call(serial_out)(early_serial_base, DLH, (divisor >> 8) & 0xff);

	static_call(serial_out)(early_serial_base, LCR, c & ~DLAB);



#if defined(CONFIG_KEXEC_CORE) && defined(CONFIG_X86_64)

	if (static_call_query(serial_in) == io_serial_in)

		kexec_debug_8250_port = early_serial_base;

#endif

}



#define DEFAULT_BAUD 9600

arch/x86/kernel/relocate_kernel_64.S

+33 −6
Original line number Diff line number Diff line
@@ -39,6 +39,7 @@ SYM_DATA(kexec_va_control_page, .quad 0) 
SYM_DATA(kexec_pa_table_page, .quad 0)

SYM_DATA(kexec_pa_swap_page, .quad 0)

SYM_DATA_LOCAL(pa_backup_pages_map, .quad 0)

SYM_DATA(kexec_debug_8250_port, .word 0)



	.balign 16

SYM_DATA_START_LOCAL(kexec_debug_gdt)
@@ -380,24 +381,50 @@ SYM_CODE_START_LOCAL_NOALIGN(swap_pages) 
SYM_CODE_END(swap_pages)



/*

 * Generic 'print character' routine (as yet unimplemented)

 * Generic 'print character' routine

 *  - %al: Character to be printed (may clobber %rax)

 *  - %rdx: MMIO address or port.

 */

SYM_CODE_START_LOCAL_NOALIGN(pr_char)

#define XMTRDY          0x20



#define TXR             0       /*  Transmit register (WRITE) */

#define LSR             5       /*  Line Status               */



SYM_CODE_START_LOCAL_NOALIGN(pr_char_8250)

	UNWIND_HINT_FUNC

	ANNOTATE_NOENDBR

	addw	$LSR, %dx

	xchg	%al, %ah

.Lxmtrdy_loop:

	inb	%dx, %al

	testb	$XMTRDY, %al

	jnz	.Lready

	rep nop

	jmp .Lxmtrdy_loop



.Lready:

	subw	$LSR, %dx

	xchg	%al, %ah

	outb	%al, %dx

pr_char_null:

	ANNOTATE_NOENDBR



	ANNOTATE_UNRET_SAFE

	ret

SYM_CODE_END(pr_char)

SYM_CODE_END(pr_char_8250)



/*

 * Load pr_char function pointer into %rsi and load %rdx with whatever

 * that function wants to see there (typically port/MMIO address).

 */

.macro pr_setup

	/* No output; pr_char just returns */

	leaq	pr_char(%rip), %rsi

	leaq	pr_char_8250(%rip), %rsi

	movw	kexec_debug_8250_port(%rip), %dx

	testw	%dx, %dx

	jnz	1f



	leaq	pr_char_null(%rip), %rsi

1:

.endm



/* Print the nybble in %bl, clobber %rax */