1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/dmi.h> 3 #include <linux/ioport.h> 4 #include <asm/e820/api.h> 5 6 static void resource_clip(struct resource *res, resource_size_t start, 7 resource_size_t end) 8 { 9 resource_size_t low = 0, high = 0; 10 11 if (res->end < start || res->start > end) 12 return; /* no conflict */ 13 14 if (res->start < start) 15 low = start - res->start; 16 17 if (res->end > end) 18 high = res->end - end; 19 20 /* Keep the area above or below the conflict, whichever is larger */ 21 if (low > high) 22 res->end = start - 1; 23 else 24 res->start = end + 1; 25 } 26 27 /* 28 * Some BIOS-es contain a bug where they add addresses which map to 29 * system RAM in the PCI host bridge window returned by the ACPI _CRS 30 * method, see commit 4dc2287c1805 ("x86: avoid E820 regions when 31 * allocating address space"). To avoid this Linux by default excludes 32 * E820 reservations when allocating addresses since 2010. 33 * In 2019 some systems have shown-up with E820 reservations which cover 34 * the entire _CRS returned PCI host bridge window, causing all attempts 35 * to assign memory to PCI BARs to fail if Linux uses E820 reservations. 36 * 37 * Ideally Linux would fully stop using E820 reservations, but then 38 * the old systems this was added for will regress. 39 * Instead keep the old behavior for old systems, while ignoring the 40 * E820 reservations for any systems from now on. 41 */ 42 static void remove_e820_regions(struct resource *avail) 43 { 44 int i, year = dmi_get_bios_year(); 45 struct e820_entry *entry; 46 47 if (year >= 2018) 48 return; 49 50 pr_info_once("PCI: Removing E820 reservations from host bridge windows\n"); 51 52 for (i = 0; i < e820_table->nr_entries; i++) { 53 entry = &e820_table->entries[i]; 54 55 resource_clip(avail, entry->addr, 56 entry->addr + entry->size - 1); 57 } 58 } 59 60 void arch_remove_reservations(struct resource *avail) 61 { 62 /* 63 * Trim out BIOS area (high 2MB) and E820 regions. We do not remove 64 * the low 1MB unconditionally, as this area is needed for some ISA 65 * cards requiring a memory range, e.g. the i82365 PCMCIA controller. 66 */ 67 if (avail->flags & IORESOURCE_MEM) { 68 resource_clip(avail, BIOS_ROM_BASE, BIOS_ROM_END); 69 70 remove_e820_regions(avail); 71 } 72 } 73