linux-kernel - [PATCH v5 19/20] x86/kexec: Add 8250 MMIO serial port output

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Message-ID: <20241205153343.3275139-20-dwmw2@infradead.org>
Date: Thu,  5 Dec 2024 15:05:25 +0000
From: David Woodhouse <dwmw2@...radead.org>
To: kexec@...ts.infradead.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	David Woodhouse <dwmw@...zon.co.uk>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Kai Huang <kai.huang@...el.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	linux-kernel@...r.kernel.org,
	Simon Horman <horms@...nel.org>,
	Dave Young <dyoung@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	jpoimboe@...nel.org,
	bsz@...zon.de
Subject: [PATCH v5 19/20] x86/kexec: Add 8250 MMIO serial port output

From: David Woodhouse <dwmw@...zon.co.uk>

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: David Woodhouse <dwmw@...zon.co.uk>
---
 arch/x86/include/asm/kexec.h         |  1 +
 arch/x86/kernel/early_printk.c       |  3 +++
 arch/x86/kernel/machine_kexec_64.c   | 22 ++++++++++++++++++++++
 arch/x86/kernel/relocate_kernel_64.S | 21 +++++++++++++++++++++
 4 files changed, 47 insertions(+)

diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
index f37d2d9fda3f..76843a174947 100644
--- a/arch/x86/include/asm/kexec.h
+++ b/arch/x86/include/asm/kexec.h
@@ -64,6 +64,7 @@ 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
 
 /*
diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c
index bf06866ee90a..14f548e095c9 100644
--- a/arch/x86/kernel/early_printk.c
+++ b/arch/x86/kernel/early_printk.c
@@ -296,6 +296,9 @@ 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);
+#ifdef CONFIG_KEXEC_DEBUG
+		kexec_debug_8250_mmio32 = bar0 & PCI_BASE_ADDRESS_MEM_MASK;
+#endif
 		write_pci_config(bus, slot, func, PCI_COMMAND,
 				 cmdreg|PCI_COMMAND_MEMORY);
 	}
diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index f9a68c6ec815..18307f3481e6 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -76,6 +76,24 @@ 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
 
+#ifdef CONFIG_KEXEC_DEBUG
+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);
+}
+#else
+static int map_mmio_serial(struct x86_mapping_info *info, pgd_t *level4p) { return 0; }
+#endif
+
+
 #ifdef CONFIG_KEXEC_FILE
 const struct kexec_file_ops * const kexec_file_loaders[] = {
 		&kexec_bzImage64_ops,
@@ -285,6 +303,10 @@ 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.
diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 01a31e4a0664..12001f389d0b 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -38,6 +38,7 @@ 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)
 
 #ifdef CONFIG_KEXEC_DEBUG
@@ -394,6 +395,21 @@ pr_char_null:
 	ret
 SYM_CODE_END(pr_char_8250)
 
+SYM_CODE_START_LOCAL_NOALIGN(pr_char_8250_mmio32)
+	UNWIND_HINT_FUNC
+.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).
@@ -404,6 +420,11 @@ 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
-- 
2.47.0