Commit 7516e721 authored by David Woodhouse's avatar David Woodhouse Committed by Ingo Molnar
Browse files

x86/kexec: Add 8250 MMIO serial port output 



This supports the same 32-bit MMIO-mapped 8250 as the early_printk code.

It's not clear why the early_printk code supports this form and only this
form; the actual runtime 8250_pci doesn't seem to support it. But having
hacked up QEMU to expose such a device, early_printk does work with it,
and now so does the kexec debug code.

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/20250326142404.256980-3-dwmw2@infradead.org
parent d358b451

arch/x86/include/asm/kexec.h

+1 −0
Original line number Diff line number Diff line
@@ -65,6 +65,7 @@ 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;

extern unsigned long kexec_debug_8250_mmio32;

#endif



/*

arch/x86/kernel/early_printk.c

+3 −0
Original line number Diff line number Diff line
@@ -333,6 +333,9 @@ static __init void early_pci_serial_init(char *s) 
		/* WARNING! assuming the address is always in the first 4G */

		early_serial_base =

			(unsigned long)early_ioremap(bar0 & PCI_BASE_ADDRESS_MEM_MASK, 0x10);

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

		kexec_debug_8250_mmio32 = bar0 & PCI_BASE_ADDRESS_MEM_MASK;

#endif

		write_pci_config(bus, slot, func, PCI_COMMAND,

				 cmdreg|PCI_COMMAND_MEMORY);

	}

arch/x86/kernel/machine_kexec_64.c

+17 −0
Original line number Diff line number Diff line
@@ -76,6 +76,19 @@ map_acpi_tables(struct x86_mapping_info *info, pgd_t *level4p) 
static int map_acpi_tables(struct x86_mapping_info *info, pgd_t *level4p) { return 0; }

#endif



static int map_mmio_serial(struct x86_mapping_info *info, pgd_t *level4p)

{

	unsigned long mstart, mend;



	if (!kexec_debug_8250_mmio32)

		return 0;



	mstart = kexec_debug_8250_mmio32 & PAGE_MASK;

	mend = (kexec_debug_8250_mmio32 + PAGE_SIZE + 23) & PAGE_MASK;

	pr_info("Map PCI serial at %lx - %lx\n", mstart, mend);

	return kernel_ident_mapping_init(info, level4p, mstart, mend);

}



#ifdef CONFIG_KEXEC_FILE

const struct kexec_file_ops * const kexec_file_loaders[] = {

		&kexec_bzImage64_ops,
@@ -285,6 +298,10 @@ static int init_pgtable(struct kimage *image, unsigned long control_page) 
	if (result)

		return result;



	result = map_mmio_serial(&info, image->arch.pgd);

	if (result)

		return result;



	/*

	 * This must be last because the intermediate page table pages it

	 * allocates will not be control pages and may overlap the image.

arch/x86/kernel/relocate_kernel_64.S

+22 −0
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_mmio32, .quad 0)

SYM_DATA(kexec_debug_8250_port, .word 0)



	.balign 16
@@ -413,6 +414,22 @@ pr_char_null: 
	ret

SYM_CODE_END(pr_char_8250)



SYM_CODE_START_LOCAL_NOALIGN(pr_char_8250_mmio32)

	UNWIND_HINT_FUNC

	ANNOTATE_NOENDBR

.Lxmtrdy_loop_mmio:

	movb	(LSR*4)(%rdx), %ah

	testb	$XMTRDY, %ah

	jnz	.Lready_mmio

	rep nop

	jmp .Lxmtrdy_loop_mmio



.Lready_mmio:

	movb	%al, (%rdx)

	ANNOTATE_UNRET_SAFE

	ret

SYM_CODE_END(pr_char_8250_mmio32)



/*

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

 * that function wants to see there (typically port/MMIO address).
@@ -423,6 +440,11 @@ SYM_CODE_END(pr_char_8250) 
	testw	%dx, %dx

	jnz	1f



	leaq	pr_char_8250_mmio32(%rip), %rsi

	movq	kexec_debug_8250_mmio32(%rip), %rdx

	testq	%rdx, %rdx

	jnz	1f



	leaq	pr_char_null(%rip), %rsi

1:

.endm