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x86/kexec: Add 8250 serial port output

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

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Ingo 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
This commit is contained in:
David Woodhouse 2025-03-26 14:16:01 +00:00 committed by Ingo Molnar
parent a23be6ccd8
commit d358b45120
3 changed files with 40 additions and 6 deletions
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1
arch/x86/include/asm/kexec.h
View File

@ -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
/*

6
arch/x86/kernel/early_printk.c
View File

@ -1,6 +1,7 @@
// 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

39
arch/x86/kernel/relocate_kernel_64.S
View File

@ -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
.macro pr_setup
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 */