[PATCH v5 1/2] 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 host bridge window returned by the ACPI _CRS method, see
commit 4dc2287c1805 ("x86: avoid E820 regions when allocating address
space").

To work around this bug Linux excludes E820 reserved addresses when
allocating addresses from the PCI host bridge window since 2010.

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]

The ACPI specifications appear to allow this new behavior:

The relationship between E820 and ACPI _CRS is not really very clear.
ACPI v6.3, sec 15, table 15-374, says AddressRangeReserved means:

  This range of addresses is in use or reserved by the system and is
  not to be included in the allocatable memory pool of the operating
  system's memory manager.

and it may be used when:

  The address range is in use by a memory-mapped system device.

Furthermore, sec 15.2 says:

  Address ranges defined for baseboard memory-mapped I/O devices, such
  as APICs, are returned as reserved.

A PCI host bridge qualifies as a baseboard memory-mapped I/O device,
and its apertures are in use and certainly should not be included in
the general allocatable pool, so the fact that some BIOS-es reports
the PCI aperture as "reserved" in E820 doesn't seem like a BIOS bug.

So it seems that the excluding of E820 reserved addresses is a mistake.

Ideally Linux would fully stop excluding E820 reserved addresses,
but then the old systems this was added for will regress.
Instead keep the old behavior for old systems, while ignoring
the E820 reservations 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 v5:
- Drop mention of Windows behavior from the commit msg, replace with a
  reference to the specs
- Improve documentation in Documentation/admin-guide/kernel-parameters.txt
- Reword the big comment added, use "PCI host bridge window" in it and drop
  all refences to Windows

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         |  9 ++++++
 arch/x86/include/asm/pci_x86.h                | 10 +++++++
 arch/x86/kernel/resource.c                    |  4 +++
 arch/x86/pci/acpi.c                           | 28 +++++++++++++++++++
 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..07f1615206d4 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3949,6 +3949,15 @@
 				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] Use E820 reservations to exclude parts of
+				PCI host bridge windows. This is a workaround
+				for BIOS defects in host bridge _CRS methods.
+				If you need to use this, please report a bug to
+				<linux-pci@xxxxxxxxxxxxxxx>.
+		no_e820		[X86] Ignore E820 reservations for PCI host
+				bridge windows. This is the default on modern
+				hardware. If you need to use this, please report
+				a bug to <linux-pci@xxxxxxxxxxxxxxx>.
 		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..72d473054262 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 +162,32 @@ 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 host bridge 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.
+	 * In 2020 some systems have shown-up with E820 reservations which cover
+	 * the entire _CRS returned PCI host bridge window, causing all attempts
+	 * to assign memory to PCI BARs to fail if Linux uses E820 reservations.
+	 *
+	 * Ideally Linux would fully stop using E820 reservations, but then
+	 * the old systems this was added for will regress.
+	 * Instead keep the old behavior for old systems, while ignoring the
+	 * E820 reservations 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 ? "Using" : "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