[PATCH v4 1/1] x86/PCI: Ignore E820 reservations for bridge windows on newer systems

[Hans de Goede]

Some BIOS-es contain a bug where they add addresses which map to system RAM
in the PCI bridge memory window returned by the ACPI _CRS method, see
commit 4dc2287c1805 ("x86: avoid E820 regions when allocating address
space").

To avoid this Linux by default excludes E820 reservations when allocating
addresses since 2010. Windows however ignores E820 reserved regions for PCI
mem allocations, so in hindsight Linux honoring them is a problem.

Recently (2020) some systems have shown-up with E820 reservations which
cover the entire _CRS returned PCI bridge memory window, causing all
attempts to assign memory to PCI BARs which have not been setup by the
BIOS to fail. For example here are the relevant dmesg bits from a
Lenovo IdeaPad 3 15IIL 81WE:

 [mem 0x000000004bc50000-0x00000000cfffffff] reserved
 pci_bus 0000:00: root bus resource [mem 0x65400000-0xbfffffff window]

Ideally Linux would fully stop honoring E820 reservations for PCI mem
allocations, but then the old systems this was added for will regress.
Instead keep the old behavior for old systems, while ignoring the E820
reservations like Windows does for any systems from now on.

Old systems are defined here as BIOS year < 2018, this was chosen to
make sure that pci_use_e820 will not be set on the currently affected
systems, while at the same time also taking into account that the
systems for which the E820 checking was originally added may have
received BIOS updates for quite a while (esp. CVE related ones),
giving them a more recent BIOS year then 2010.

Also add pci=no_e820 and pci=use_e820 options to allow overriding
the BIOS year heuristic.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=206459
BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1868899
BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1871793
BugLink: https://bugs.launchpad.net/bugs/1878279
BugLink: https://bugs.launchpad.net/bugs/1931715
BugLink: https://bugs.launchpad.net/bugs/1932069
BugLink: https://bugs.launchpad.net/bugs/1921649
Cc: Benoit Grégoire <benoitg@xxxxxxxx>
Cc: Hui Wang <hui.wang@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
---
Changes in v4:
- Rewrap the big comment block to fit in 80 columns
- Add Rafael's Acked-by
- Add Cc: stable@xxxxxxxxxxxxxxx

Changes in v3:
- Commit msg tweaks (drop dmesg timestamps, typo fix)
- Use "defined(CONFIG_...)" instead of "defined CONFIG_..."
- Add Mika's Reviewed-by

Changes in v2:
- Replace the per model DMI quirk approach with disabling E820 reservations
  checking for all systems with a BIOS year >= 2018
- Add documentation for the new kernel-parameters to
  Documentation/admin-guide/kernel-parameters.txt
---
Other patches trying to address the same issue:
https://lore.kernel.org/r/20210624095324.34906-1-hui.wang@xxxxxxxxxxxxx
https://lore.kernel.org/r/20200617164734.84845-1-mika.westerberg@xxxxxxxxxxxxxxx
V1 patch:
https://lore.kernel.org/r/20211005150956.303707-1-hdegoede@xxxxxxxxxx
---
 .../admin-guide/kernel-parameters.txt         |  6 ++++
 arch/x86/include/asm/pci_x86.h                | 10 ++++++
 arch/x86/kernel/resource.c                    |  4 +++
 arch/x86/pci/acpi.c                           | 31 +++++++++++++++++++
 arch/x86/pci/common.c                         |  6 ++++
 5 files changed, 57 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 43dc35fe5bc0..969cde5d74c8 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3949,6 +3949,12 @@
 				please report a bug.
 		nocrs		[X86] Ignore PCI host bridge windows from ACPI.
 				If you need to use this, please report a bug.
+		use_e820	[X86] Honor E820 reservations when allocating
+				PCI host bridge memory. If you need to use this,
+				please report a bug.
+		no_e820		[X86] ignore E820 reservations when allocating
+				PCI host bridge memory. If you need to use this,
+				please report a bug.
 		routeirq	Do IRQ routing for all PCI devices.
 				This is normally done in pci_enable_device(),
 				so this option is a temporary workaround
diff --git a/arch/x86/include/asm/pci_x86.h b/arch/x86/include/asm/pci_x86.h
index 490411dba438..0bb4e7dd0ffc 100644
--- a/arch/x86/include/asm/pci_x86.h
+++ b/arch/x86/include/asm/pci_x86.h
@@ -39,6 +39,8 @@ do {						\
 #define PCI_ROOT_NO_CRS		0x100000
 #define PCI_NOASSIGN_BARS	0x200000
 #define PCI_BIG_ROOT_WINDOW	0x400000
+#define PCI_USE_E820		0x800000
+#define PCI_NO_E820		0x1000000
 
 extern unsigned int pci_probe;
 extern unsigned long pirq_table_addr;
@@ -64,6 +66,8 @@ void pcibios_scan_specific_bus(int busn);
 
 /* pci-irq.c */
 
+struct pci_dev;
+
 struct irq_info {
 	u8 bus, devfn;			/* Bus, device and function */
 	struct {
@@ -232,3 +236,9 @@ static inline void mmio_config_writel(void __iomem *pos, u32 val)
 # define x86_default_pci_init_irq	NULL
 # define x86_default_pci_fixup_irqs	NULL
 #endif
+
+#if defined(CONFIG_PCI) && defined(CONFIG_ACPI)
+extern bool pci_use_e820;
+#else
+#define pci_use_e820 false
+#endif
diff --git a/arch/x86/kernel/resource.c b/arch/x86/kernel/resource.c
index 9b9fb7882c20..e8dc9bc327bd 100644
--- a/arch/x86/kernel/resource.c
+++ b/arch/x86/kernel/resource.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/ioport.h>
 #include <asm/e820/api.h>
+#include <asm/pci_x86.h>
 
 static void resource_clip(struct resource *res, resource_size_t start,
 			  resource_size_t end)
@@ -28,6 +29,9 @@ static void remove_e820_regions(struct resource *avail)
 	int i;
 	struct e820_entry *entry;
 
+	if (!pci_use_e820)
+		return;
+
 	for (i = 0; i < e820_table->nr_entries; i++) {
 		entry = &e820_table->entries[i];
 
diff --git a/arch/x86/pci/acpi.c b/arch/x86/pci/acpi.c
index 948656069cdd..4537e3561c91 100644
--- a/arch/x86/pci/acpi.c
+++ b/arch/x86/pci/acpi.c
@@ -21,6 +21,8 @@ struct pci_root_info {
 
 static bool pci_use_crs = true;
 static bool pci_ignore_seg = false;
+/* Consumed in arch/x86/kernel/resource.c */
+bool pci_use_e820 = false;
 
 static int __init set_use_crs(const struct dmi_system_id *id)
 {
@@ -160,6 +162,35 @@ void __init pci_acpi_crs_quirks(void)
 	       "if necessary, use \"pci=%s\" and report a bug\n",
 	       pci_use_crs ? "Using" : "Ignoring",
 	       pci_use_crs ? "nocrs" : "use_crs");
+
+	/*
+	 * Some BIOS-es contain a bug where they add addresses which map to
+	 * system RAM in the PCI bridge memory window returned by the ACPI _CRS
+	 * method, see commit 4dc2287c1805 ("x86: avoid E820 regions when
+	 * allocating address space"). To avoid this Linux by default excludes
+	 * E820 reservations when allocating addresses since 2010.
+	 * Windows however ignores E820 reserved regions for PCI allocations,
+	 * so in hindsight Linux honoring them is a problem.
+	 * In 2020 some systems have shown-up with E820 reservations which
+	 * cover the entire _CRS returned PCI bridge memory window, causing
+	 * all attempts to assign memory to PCI BARs to fail if Linux honors
+	 * the E820 reservations.
+	 *
+	 * Ideally Linux would fully stop honoring E820 reservations for PCI mem
+	 * allocations, but then older systems this was added for will regress.
+	 * Instead keep the old behavior for old systems, while ignoring the
+	 * E820 reservations like Windows does for any systems from now on.
+	 */
+	if (year >= 0 && year < 2018)
+		pci_use_e820 = true;
+
+	if (pci_probe & PCI_NO_E820)
+		pci_use_e820 = false;
+	else if (pci_probe & PCI_USE_E820)
+		pci_use_e820 = true;
+
+	printk(KERN_INFO "PCI: %s E820 reservations for host bridge windows\n",
+	       pci_use_e820 ? "Honoring" : "Ignoring");
 }
 
 #ifdef	CONFIG_PCI_MMCONFIG
diff --git a/arch/x86/pci/common.c b/arch/x86/pci/common.c
index 3507f456fcd0..091ec7e94fcb 100644
--- a/arch/x86/pci/common.c
+++ b/arch/x86/pci/common.c
@@ -595,6 +595,12 @@ char *__init pcibios_setup(char *str)
 	} else if (!strcmp(str, "nocrs")) {
 		pci_probe |= PCI_ROOT_NO_CRS;
 		return NULL;
+	} else if (!strcmp(str, "use_e820")) {
+		pci_probe |= PCI_USE_E820;
+		return NULL;
+	} else if (!strcmp(str, "no_e820")) {
+		pci_probe |= PCI_NO_E820;
+		return NULL;
 #ifdef CONFIG_PHYS_ADDR_T_64BIT
 	} else if (!strcmp(str, "big_root_window")) {
 		pci_probe |= PCI_BIG_ROOT_WINDOW;
-- 
2.31.1