Re: [PATCH v5 1/2] x86/PCI: Ignore E820 reservations for bridge windows on newer systems

From: Bjorn Helgaas
Date: Fri Oct 15 2021 - 16:03:42 EST

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On Thu, Oct 14, 2021 at 08:39:42PM +0200, Hans de Goede wrote:
> 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>

Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>

I'm sorry we have to add more ugliness because of my mistake in
4dc2287c1805, but I don't see a better option.

> ---
> 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
>

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