From: Andrea Arcangeli Subject: reserved-ram From: Andrea Arcangeli The "reserved RAM" can be mapped by virtualization software with /dev/mem to create a 1:1 mapping between guest physical (bus) address and host physical (bus) address. This will allow pci passthrough with DMA for the guest using the ram with the 1:1 mapping. The only detail to take care of is the ram marked "reserved RAM failed". The virtualization software must create for the guest an e820 map that only includes the "reserved RAM" regions but if the guest touches memory with guest physical address in the "reserved RAM failed" ranges (linux guest will do that even if the ram isn't present in the e820 map), it should provide that as ram and map it with a non linear mapping. This should allow any linux kernel to run fine and hopefully any other OS too. svm ~ # cat /proc/iomem |head -n 20 00000000-00000fff : reserved RAM failed 00001000-00005fff : reserved RAM 00006000-00007fff : reserved RAM failed 00008000-0009efff : reserved RAM 0009f000-0009ffff : reserved 000cd600-000cffff : pnp 00:0d 000f0000-000fffff : reserved 00100000-0fffffff : reserved RAM 10000000-3dedffff : System RAM 10000000-10329ab2 : Kernel code 10329ab3-104933e7 : Kernel data 104f5000-10558e67 : Kernel bss 3dee0000-3dee2fff : ACPI Non-volatile Storage 3dee3000-3deeffff : ACPI Tables 3def0000-3defffff : reserved 3dff0000-3ffeffff : pnp 00:0d e0000000-efffffff : reserved fa000000-fbffffff : PCI Bus #01 fa000000-fbffffff : 0000:01:05.0 fda00000-fdbfffff : PCI Bus #01 svm ~ # hexdump /dev/mem | grep -C2 'cccc cccc cccc cccc' 00007e0 0000 0000 0000 0000 0000 0000 0000 0000 * 0001000 cccc cccc cccc cccc cccc cccc cccc cccc * 0006000 a5a5 a5a5 8ec8 8ed8 8ec0 66d0 06c7 0000 -- * 0007ff0 0000 0000 0000 0000 3063 1000 0000 0000 0008000 cccc cccc cccc cccc cccc cccc cccc cccc * 009f000 0002 0000 0000 0000 0000 0000 0000 0000 -- 00fffe0 6000 3c03 45e7 0184 0500 0082 01c0 0223 00ffff0 5bea 00e0 31f0 2f32 3931 302f 0037 12fc 0100000 cccc cccc cccc cccc cccc cccc cccc cccc * 10000000 8d48 f92d ffff 48ff ed81 0000 1000 8948 ^C svm ~ # Signed-off-by: Andrea Arcangeli diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -1198,8 +1198,36 @@ config CRASH_DUMP (CONFIG_RELOCATABLE=y). For more details see Documentation/kdump/kdump.txt +config RESERVE_PHYSICAL_START + bool "Reserve all RAM below PHYSICAL_START (EXPERIMENTAL)" + depends on !RELOCATABLE && X86_64 + help + This makes the kernel use only RAM above __PHYSICAL_START. + All memory below __PHYSICAL_START will be left unused and + marked as "reserved RAM" in /proc/iomem. The few special + pages that can't be relocated at addresses above + __PHYSICAL_START and that can't be guaranteed to be unused + by the running kernel will be marked "reserved RAM failed" + in /proc/iomem. Those may or may be not used by the kernel + (for example SMP trampoline pages would only be used if + CPU hotplug is enabled). + + The "reserved RAM" can be mapped by virtualization software + with /dev/mem to create a 1:1 mapping between guest physical + (bus) address and host physical (bus) address. This will + allow PCI passthrough with DMA for the guest using the RAM + with the 1:1 mapping. The only detail to take care of is the + RAM marked "reserved RAM failed". The virtualization + software must create for the guest an e820 map that only + includes the "reserved RAM" regions but if the guest touches + memory with guest physical address in the "reserved RAM + failed" ranges (Linux guest will do that even if the RAM + isn't present in the e820 map), it should provide that as + RAM and map it with a non-linear mapping. This should allow + any Linux kernel to run fine and hopefully any other OS too. + config PHYSICAL_START - hex "Physical address where the kernel is loaded" if (EMBEDDED || CRASH_DUMP) + hex "Physical address where the kernel is loaded" if (EMBEDDED || CRASH_DUMP || RESERVE_PHYSICAL_START) default "0x1000000" if X86_NUMAQ default "0x200000" if X86_64 default "0x100000" diff --git a/arch/x86/kernel/e820_64.c b/arch/x86/kernel/e820_64.c --- a/arch/x86/kernel/e820_64.c +++ b/arch/x86/kernel/e820_64.c @@ -119,7 +119,31 @@ void __init early_res_to_bootmem(unsigne printk(KERN_INFO " early res: %d [%lx-%lx] %s\n", i, final_start, final_end - 1, r->name); reserve_bootmem_generic(final_start, final_end - final_start); +#ifdef CONFIG_RESERVE_PHYSICAL_START + if (r->start < __PHYSICAL_START) + add_memory_region(r->start, r->end - r->start, + E820_RESERVED_RAM_FAILED); +#endif } +#ifdef CONFIG_RESERVE_PHYSICAL_START + /* solve E820_RESERVED_RAM vs E820_RESERVED_RAM_FAILED conflicts */ + update_e820(); + + /* now reserve E820_RESERVED_RAM */ + for (i = 0; i < e820.nr_map; i++) { + struct e820entry *ei = &e820.map[i]; + + if (ei->type != E820_RESERVED_RAM) + continue; + final_start = max(start, (unsigned long) ei->addr); + final_end = min(end, (unsigned long) (ei->addr + ei->size)); + if (final_start >= final_end) + continue; + reserve_bootmem_generic(final_start, final_end - final_start); + printk(KERN_INFO " bootmem reserved RAM: [%lx-%lx]\n", + final_start, final_end - 1); + } +#endif } /* Check for already reserved areas */ @@ -336,6 +360,16 @@ void __init e820_reserve_resources(void) case E820_RAM: res->name = "System RAM"; break; case E820_ACPI: res->name = "ACPI Tables"; break; case E820_NVS: res->name = "ACPI Non-volatile Storage"; break; +#ifdef CONFIG_RESERVE_PHYSICAL_START + case E820_RESERVED_RAM_FAILED: + res->name = "reserved RAM failed"; + break; + case E820_RESERVED_RAM: + memset(__va(e820.map[i].addr), + POISON_FREE_INITMEM, e820.map[i].size); + res->name = "reserved RAM"; + break; +#endif default: res->name = "reserved"; } res->start = e820.map[i].addr; @@ -377,6 +411,16 @@ void __init e820_mark_nosave_regions(voi } } +static int __init e820_is_not_ram(int type) +{ +#ifdef CONFIG_RESERVE_PHYSICAL_START + return type != E820_RAM && type != E820_RESERVED_RAM && + type != E820_RESERVED_RAM_FAILED; +#else + return type != E820_RAM; +#endif +} + /* * Finds an active region in the address range from start_pfn to end_pfn and * returns its range in ei_startpfn and ei_endpfn for the e820 entry. @@ -395,11 +439,11 @@ static int __init e820_find_active_regio return 0; /* Check if max_pfn_mapped should be updated */ - if (ei->type != E820_RAM && *ei_endpfn > max_pfn_mapped) + if (e820_is_not_ram(ei->type) && *ei_endpfn > max_pfn_mapped) max_pfn_mapped = *ei_endpfn; /* Skip if map is outside the node */ - if (ei->type != E820_RAM || *ei_endpfn <= start_pfn || + if (e820_is_not_ram(ei->type) || *ei_endpfn <= start_pfn || *ei_startpfn >= end_pfn) return 0; @@ -495,6 +539,14 @@ static void __init e820_print_map(char * case E820_NVS: printk(KERN_CONT "(ACPI NVS)\n"); break; +#ifdef CONFIG_RESERVE_PHYSICAL_START + case E820_RESERVED_RAM: + printk(KERN_CONT "(reserved RAM)\n"); + break; + case E820_RESERVED_RAM_FAILED: + printk(KERN_CONT "(reserved RAM failed)\n"); + break; +#endif default: printk(KERN_CONT "type %u\n", e820.map[i].type); break; @@ -724,9 +776,31 @@ static int __init copy_e820_map(struct e u64 end = start + size; u32 type = biosmap->type; +#ifdef CONFIG_RESERVE_PHYSICAL_START + /* make space for two more low-prio types */ + type += 2; +#endif + /* Overflow in 64 bits? Ignore the memory map. */ if (start > end) return -1; + +#ifdef CONFIG_RESERVE_PHYSICAL_START + if (type == E820_RAM) { + if (end <= __PHYSICAL_START) { + add_memory_region(start, size, + E820_RESERVED_RAM); + continue; + } + if (start < __PHYSICAL_START) { + add_memory_region(start, + __PHYSICAL_START-start, + E820_RESERVED_RAM); + size -= __PHYSICAL_START-start; + start = __PHYSICAL_START; + } + } +#endif add_memory_region(start, size, type); } while (biosmap++, --nr_map); diff --git a/include/asm-x86/e820.h b/include/asm-x86/e820.h --- a/include/asm-x86/e820.h +++ b/include/asm-x86/e820.h @@ -4,10 +4,19 @@ #define E820MAX 128 /* number of entries in E820MAP */ #define E820NR 0x1e8 /* # entries in E820MAP */ +#ifdef CONFIG_RESERVE_PHYSICAL_START +#define E820_RESERVED_RAM 1 +#define E820_RESERVED_RAM_FAILED 2 +#define E820_RAM 3 +#define E820_RESERVED 4 +#define E820_ACPI 5 +#define E820_NVS 6 +#else #define E820_RAM 1 #define E820_RESERVED 2 #define E820_ACPI 3 #define E820_NVS 4 +#endif #ifndef __ASSEMBLY__ struct e820entry { diff --git a/include/asm-x86/page_64.h b/include/asm-x86/page_64.h --- a/include/asm-x86/page_64.h +++ b/include/asm-x86/page_64.h @@ -29,6 +29,7 @@ #define __PAGE_OFFSET _AC(0xffff810000000000, UL) #define __PHYSICAL_START CONFIG_PHYSICAL_START +#define __PHYSICAL_OFFSET (__PHYSICAL_START-0x200000) #define __KERNEL_ALIGN 0x200000 /* @@ -51,7 +52,7 @@ * Kernel image size is limited to 512 MB (see level2_kernel_pgt in * arch/x86/kernel/head_64.S), and it is mapped here: */ -#define KERNEL_IMAGE_SIZE (512 * 1024 * 1024) +#define KERNEL_IMAGE_SIZE (512 * 1024 * 1024 + __PHYSICAL_OFFSET) #define KERNEL_IMAGE_START _AC(0xffffffff80000000, UL) #ifndef __ASSEMBLY__ diff --git a/include/asm-x86/pgtable_64.h b/include/asm-x86/pgtable_64.h --- a/include/asm-x86/pgtable_64.h +++ b/include/asm-x86/pgtable_64.h @@ -145,7 +145,7 @@ static inline void native_pgd_clear(pgd_ #define VMALLOC_START _AC(0xffffc20000000000, UL) #define VMALLOC_END _AC(0xffffe1ffffffffff, UL) #define VMEMMAP_START _AC(0xffffe20000000000, UL) -#define MODULES_VADDR _AC(0xffffffffa0000000, UL) +#define MODULES_VADDR (0xffffffffa0000000UL+__PHYSICAL_OFFSET) #define MODULES_END _AC(0xfffffffffff00000, UL) #define MODULES_LEN (MODULES_END - MODULES_VADDR) diff --git a/include/asm-x86/trampoline.h b/include/asm-x86/trampoline.h --- a/include/asm-x86/trampoline.h +++ b/include/asm-x86/trampoline.h @@ -13,7 +13,11 @@ extern unsigned long init_rsp; extern unsigned long init_rsp; extern unsigned long initial_code; +#ifndef CONFIG_RESERVE_PHYSICAL_START #define TRAMPOLINE_BASE 0x6000 +#else +#define TRAMPOLINE_BASE 0x90000 /* move it next to 640k */ +#endif extern unsigned long setup_trampoline(void); #endif /* __ASSEMBLY__ */