Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull more x86 fixes from Peter Anvin:
 "Additional x86 fixes.  Three of these patches are pure documentation,
  two are pretty trivial; the remaining one fixes boot problems on some
  non-BIOS machines."

* 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86: Make sure we can boot in the case the BDA contains pure garbage
  x86, efi: Mark disable_runtime as __initdata
  x86, doc: Fix incorrect comment about 64-bit code segment descriptors
  doc, kernel-parameters: Document 'console=hvc<n>'
  doc, xen: Mention 'earlyprintk=xen' in the documentation.
  ACPI: Overriding ACPI tables via initrd only works with an initrd and on X86

5 files changed, 44 insertions, 23 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 1da946548772..e567af39ee34 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -564,6 +564,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         UART at the specified I/O port or MMIO address,
                         switching to the matching ttyS device later.  The
                         options are the same as for ttyS, above.
+                hvc<n>  Use the hypervisor console device <n>. This is for
+                        both Xen and PowerPC hypervisors.
 
                 If the device connected to the port is not a TTY but a braille
                 device, prepend "brl," before the device type, for instance
@@ -757,6 +759,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 
         earlyprintk=    [X86,SH,BLACKFIN]
                         earlyprintk=vga
+                        earlyprintk=xen
                         earlyprintk=serial[,ttySn[,baudrate]]
                         earlyprintk=ttySn[,baudrate]
                         earlyprintk=dbgp[debugController#]
@@ -774,6 +777,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         The VGA output is eventually overwritten by the real
                         console.
 
+                        The xen output can only be used by Xen PV guests.
+
         ekgdboc=        [X86,KGDB] Allow early kernel console debugging
                         ekgdboc=kbd
 
diff --git a/arch/x86/kernel/head.c b/arch/x86/kernel/head.c
index 48d9d4ea1020..992f442ca155 100644
--- a/arch/x86/kernel/head.c
+++ b/arch/x86/kernel/head.c
@@ -5,8 +5,6 @@
 #include <asm/setup.h>
 #include <asm/bios_ebda.h>
 
-#define BIOS_LOWMEM_KILOBYTES 0x413
-
 /*
  * The BIOS places the EBDA/XBDA at the top of conventional
  * memory, and usually decreases the reported amount of
@@ -16,17 +14,30 @@
  * chipset: reserve a page before VGA to prevent PCI prefetch
  * into it (errata #56). Usually the page is reserved anyways,
  * unless you have no PS/2 mouse plugged in.
+ *
+ * This functions is deliberately very conservative.  Losing
+ * memory in the bottom megabyte is rarely a problem, as long
+ * as we have enough memory to install the trampoline.  Using
+ * memory that is in use by the BIOS or by some DMA device
+ * the BIOS didn't shut down *is* a big problem.
  */
+
+#define BIOS_LOWMEM_KILOBYTES   0x413
+#define LOWMEM_CAP              0x9f000U        /* Absolute maximum */
+#define INSANE_CUTOFF           0x20000U        /* Less than this = insane */
+
 void __init reserve_ebda_region(void)
 {
         unsigned int lowmem, ebda_addr;
 
-        /* To determine the position of the EBDA and the */
-        /* end of conventional memory, we need to look at */
-        /* the BIOS data area. In a paravirtual environment */
-        /* that area is absent. We'll just have to assume */
-        /* that the paravirt case can handle memory setup */
-        /* correctly, without our help. */
+        /*
+         * To determine the position of the EBDA and the
+         * end of conventional memory, we need to look at
+         * the BIOS data area. In a paravirtual environment
+         * that area is absent. We'll just have to assume
+         * that the paravirt case can handle memory setup
+         * correctly, without our help.
+         */
         if (paravirt_enabled())
                 return;
 
@@ -37,19 +48,23 @@ void __init reserve_ebda_region(void)
         /* start of EBDA area */
         ebda_addr = get_bios_ebda();
 
-        /* Fixup: bios puts an EBDA in the top 64K segment */
-        /* of conventional memory, but does not adjust lowmem. */
-        if ((lowmem - ebda_addr) <= 0x10000)
-                lowmem = ebda_addr;
+        /*
+         * Note: some old Dells seem to need 4k EBDA without
+         * reporting so, so just consider the memory above 0x9f000
+         * to be off limits (bugzilla 2990).
+         */
+
+        /* If the EBDA address is below 128K, assume it is bogus */
+        if (ebda_addr < INSANE_CUTOFF)
+                ebda_addr = LOWMEM_CAP;
 
-        /* Fixup: bios does not report an EBDA at all. */
-        /* Some old Dells seem to need 4k anyhow (bugzilla 2990) */
-        if ((ebda_addr == 0) && (lowmem >= 0x9f000))
-                lowmem = 0x9f000;
+        /* If lowmem is less than 128K, assume it is bogus */
+        if (lowmem < INSANE_CUTOFF)
+                lowmem = LOWMEM_CAP;
 
-        /* Paranoia: should never happen, but... */
-        if ((lowmem == 0) || (lowmem >= 0x100000))
-                lowmem = 0x9f000;
+        /* Use the lower of the lowmem and EBDA markers as the cutoff */
+        lowmem = min(lowmem, ebda_addr);
+        lowmem = min(lowmem, LOWMEM_CAP); /* Absolute cap */
 
         /* reserve all memory between lowmem and the 1MB mark */
         memblock_reserve(lowmem, 0x100000 - lowmem);
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index b7de3b25adb5..6859e9626442 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -48,7 +48,7 @@ L3_START_KERNEL = pud_index(__START_KERNEL_map)
         .globl startup_64
 startup_64:
         /*
-         * At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 1,
+         * At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 0,
          * and someone has loaded an identity mapped page table
          * for us.  These identity mapped page tables map all of the
          * kernel pages and possibly all of memory.
@@ -159,7 +159,7 @@ startup_64:
         jmp 1f
 ENTRY(secondary_startup_64)
         /*
-         * At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 1,
+         * At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 0,
          * and someone has loaded a mapped page table.
          *
          * %rsi holds a physical pointer to real_mode_data.
diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index 2f81db40d7ca..5ae99f9160d9 100644
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -85,7 +85,7 @@ int efi_enabled(int facility)
 }
 EXPORT_SYMBOL(efi_enabled);
 
-static bool disable_runtime = false;
+static bool __initdata disable_runtime = false;
 static int __init setup_noefi(char *arg)
 {
         disable_runtime = true;
diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index 320006019e68..92ed9692c47e 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -266,7 +266,8 @@ config ACPI_CUSTOM_DSDT
         default ACPI_CUSTOM_DSDT_FILE != ""
 
 config ACPI_INITRD_TABLE_OVERRIDE
-        bool "ACPI tables can be passed via uncompressed cpio in initrd"
+        bool "ACPI tables override via initrd"
+        depends on BLK_DEV_INITRD && X86
         default n
         help
           This option provides functionality to override arbitrary ACPI tables