x86, realmode: Relocator for realmode code

Implements relocator for real mode code that is called
as part of setup_arch(). Processes segment relocations
and linear relocations. Real-mode code is relocated to
a free hole below 1 MB.

Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@intel.com>
Link: http://lkml.kernel.org/r/1336501366-28617-4-git-send-email-jarkko.sakkinen@intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

4 files changed, 108 insertions, 0 deletions

diff --git a/arch/x86/include/asm/realmode.h b/arch/x86/include/asm/realmode.h
new file mode 100644
index 000000000000..dc1bba534c14
--- /dev/null
+++ b/arch/x86/include/asm/realmode.h
@@ -0,0 +1,26 @@
+#ifndef _ARCH_X86_REALMODE_H
+#define _ARCH_X86_REALMODE_H
+
+#include <linux/types.h>
+#include <asm/io.h>
+
+/* This must match data at realmode.S */
+struct real_mode_header {
+        u32     text_start;
+        u32     ro_end;
+        u32     end;
+} __attribute__((__packed__));
+
+extern struct real_mode_header real_mode_header;
+extern unsigned char *real_mode_base;
+
+extern unsigned long init_rsp;
+extern unsigned long initial_code;
+extern unsigned long initial_gs;
+
+extern unsigned char real_mode_blob[];
+extern unsigned char real_mode_relocs[];
+
+extern void __init setup_real_mode(void);
+
+#endif /* _ARCH_X86_REALMODE_H */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 532d2e090e6f..f9e19d4eb984 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -36,6 +36,7 @@ obj-y			+= pci-iommu_table.o
 obj-y                   += resource.o
 
 obj-y                           += trampoline.o trampoline_$(BITS).o
+obj-y                           += realmode.o
 obj-y                           += process.o
 obj-y                           += i387.o xsave.o
 obj-y                           += ptrace.o
diff --git a/arch/x86/kernel/realmode.c b/arch/x86/kernel/realmode.c
new file mode 100644
index 000000000000..7415c42547ac
--- /dev/null
+++ b/arch/x86/kernel/realmode.c
@@ -0,0 +1,79 @@
+#include <linux/io.h>
+#include <linux/memblock.h>
+
+#include <asm/cacheflush.h>
+#include <asm/pgtable.h>
+#include <asm/realmode.h>
+
+unsigned char *real_mode_base;
+struct real_mode_header real_mode_header;
+
+void __init setup_real_mode(void)
+{
+        phys_addr_t mem;
+        u16 real_mode_seg;
+        u32 *rel;
+        u32 count;
+        u32 *ptr;
+        u16 *seg;
+        int i;
+
+        struct real_mode_header *header =
+                (struct real_mode_header *) real_mode_blob;
+
+        size_t size = PAGE_ALIGN(header->end);
+
+        /* Has to be in very low memory so we can execute real-mode AP code. */
+        mem = memblock_find_in_range(0, 1<<20, size, PAGE_SIZE);
+        if (!mem)
+                panic("Cannot allocate trampoline\n");
+
+        real_mode_base = __va(mem);
+        memblock_reserve(mem, size);
+
+        printk(KERN_DEBUG "Base memory trampoline at [%p] %llx size %zu\n",
+               real_mode_base, (unsigned long long)mem, size);
+
+        memcpy(real_mode_base, real_mode_blob, size);
+
+        real_mode_seg = __pa(real_mode_base) >> 4;
+        rel = (u32 *) real_mode_relocs;
+
+        /* 16-bit segment relocations. */
+        count = rel[0];
+        rel = &rel[1];
+        for (i = 0; i < count; i++) {
+                seg = (u16 *) (real_mode_base + rel[i]);
+                *seg = real_mode_seg;
+        }
+
+        /* 32-bit linear relocations. */
+        count = rel[i];
+        rel =  &rel[i + 1];
+        for (i = 0; i < count; i++) {
+                ptr = (u32 *) (real_mode_base + rel[i]);
+                *ptr += __pa(real_mode_base);
+        }
+
+        /* Copied header will contain relocated physical addresses. */
+        memcpy(&real_mode_header, real_mode_base,
+               sizeof(struct real_mode_header));
+}
+
+/*
+ * set_real_mode_permissions() gets called very early, to guarantee the
+ * availability of low memory.  This is before the proper kernel page
+ * tables are set up, so we cannot set page permissions in that
+ * function.  Thus, we use an arch_initcall instead.
+ */
+static int __init set_real_mode_permissions(void)
+{
+        size_t all_size =
+                PAGE_ALIGN(real_mode_header.end) -
+                __pa(real_mode_base);
+
+        set_memory_x((unsigned long) real_mode_base, all_size >> PAGE_SHIFT);
+        return 0;
+}
+
+arch_initcall(set_real_mode_permissions);
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 1a2901562059..56e41242a6b8 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -74,6 +74,7 @@
 #include <asm/mtrr.h>
 #include <asm/apic.h>
 #include <asm/trampoline.h>
+#include <asm/realmode.h>
 #include <asm/e820.h>
 #include <asm/mpspec.h>
 #include <asm/setup.h>
@@ -918,6 +919,7 @@ void __init setup_arch(char **cmdline_p)
                         max_pfn_mapped<<PAGE_SHIFT);
 
         setup_trampolines();
+        setup_real_mode();
 
         init_gbpages();