mirror of https://github.com/torvalds/linux.git
73 lines
2.1 KiB
C
73 lines
2.1 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/dmi.h>
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#include <linux/ioport.h>
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#include <asm/e820/api.h>
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static void resource_clip(struct resource *res, resource_size_t start,
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resource_size_t end)
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{
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resource_size_t low = 0, high = 0;
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if (res->end < start || res->start > end)
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return; /* no conflict */
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if (res->start < start)
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low = start - res->start;
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if (res->end > end)
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high = res->end - end;
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/* Keep the area above or below the conflict, whichever is larger */
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if (low > high)
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res->end = start - 1;
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else
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res->start = end + 1;
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}
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/*
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* Some BIOS-es contain a bug where they add addresses which map to
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* system RAM in the PCI host bridge window returned by the ACPI _CRS
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* method, see commit 4dc2287c1805 ("x86: avoid E820 regions when
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* allocating address space"). To avoid this Linux by default excludes
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* E820 reservations when allocating addresses since 2010.
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* In 2019 some systems have shown-up with E820 reservations which cover
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* the entire _CRS returned PCI host bridge window, causing all attempts
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* to assign memory to PCI BARs to fail if Linux uses E820 reservations.
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*
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* Ideally Linux would fully stop using E820 reservations, but then
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* the old systems this was added for will regress.
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* Instead keep the old behavior for old systems, while ignoring the
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* E820 reservations for any systems from now on.
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*/
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static void remove_e820_regions(struct resource *avail)
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{
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int i, year = dmi_get_bios_year();
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struct e820_entry *entry;
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if (year >= 2018)
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return;
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pr_info_once("PCI: Removing E820 reservations from host bridge windows\n");
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for (i = 0; i < e820_table->nr_entries; i++) {
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entry = &e820_table->entries[i];
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resource_clip(avail, entry->addr,
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entry->addr + entry->size - 1);
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}
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}
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void arch_remove_reservations(struct resource *avail)
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{
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/*
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* Trim out BIOS area (high 2MB) and E820 regions. We do not remove
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* the low 1MB unconditionally, as this area is needed for some ISA
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* cards requiring a memory range, e.g. the i82365 PCMCIA controller.
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*/
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if (avail->flags & IORESOURCE_MEM) {
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resource_clip(avail, BIOS_ROM_BASE, BIOS_ROM_END);
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remove_e820_regions(avail);
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}
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}
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