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    SubjectRe: [PATCH v5 1/2] x86/PCI: Ignore E820 reservations for bridge windows on newer systems
    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@coeus.ca>
    > Cc: Hui Wang <hui.wang@canonical.com>
    > Cc: stable@vger.kernel.org
    > Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
    > Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    > Signed-off-by: Hans de Goede <hdegoede@redhat.com>

    Acked-by: Bjorn Helgaas <bhelgaas@google.com>

    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@vger.kernel.org
    >
    > 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@canonical.com
    > https://lore.kernel.org/r/20200617164734.84845-1-mika.westerberg@linux.intel.com
    > V1 patch:
    > https://lore.kernel.org/r/20211005150956.303707-1-hdegoede@redhat.com
    > ---
    > .../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@vger.kernel.org>.
    > + 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@vger.kernel.org>.
    > 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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