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https://github.com/BobTheBlinker/android_kernel_motorola_sm6375.git
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Boot with virtual == physical to get closer to native Linux.
1) This allows us to get alot closer to booting bzImages. 2) It means we don't have to know page_offset. 3) The Guest needs to modify the boot pagetables to create the PAGE_OFFSET mapping before jumping to C code. 4) guest_pa() walks the page tables rather than using page_offset. 5) We don't use page_offset to figure out whether to emulate: it was always kinda quesationable, and won't work for instructions done before remapping (bzImage unpacking in particular). 6) We still want the kernel address for tlb flushing: have the initial hypercall give us that, too. Signed-off-by: Rusty Russell <[email protected]>
This commit is contained in:
Rusty Russell
parent
c18acd73ff
commit
47436aa4ad
12 changed files with 141 additions and 148 deletions
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@ -178,19 +178,16 @@ static void *get_pages(unsigned int num)
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/* To find out where to start we look for the magic Guest string, which marks
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* the code we see in lguest_asm.S. This is a hack which we are currently
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* plotting to replace with the normal Linux entry point. */
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static unsigned long entry_point(const void *start, const void *end,
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unsigned long page_offset)
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static unsigned long entry_point(const void *start, const void *end)
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{
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const void *p;
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/* The scan gives us the physical starting address. We want the
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* virtual address in this case, and fortunately, we already figured
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* out the physical-virtual difference and passed it here in
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* "page_offset". */
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/* The scan gives us the physical starting address. We boot with
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* pagetables set up with virtual and physical the same, so that's
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* OK. */
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for (p = start; p < end; p++)
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if (memcmp(p, "GenuineLguest", strlen("GenuineLguest")) == 0)
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return to_guest_phys(p + strlen("GenuineLguest"))
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+ page_offset;
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return to_guest_phys(p + strlen("GenuineLguest"));
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errx(1, "Is this image a genuine lguest?");
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}
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@ -224,14 +221,11 @@ static void map_at(int fd, void *addr, unsigned long offset, unsigned long len)
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* by all modern binaries on Linux including the kernel.
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*
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* The ELF headers give *two* addresses: a physical address, and a virtual
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* address. The Guest kernel expects to be placed in memory at the physical
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* address, and the page tables set up so it will correspond to that virtual
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* address. We return the difference between the virtual and physical
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* addresses in the "page_offset" pointer.
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* address. We use the physical address; the Guest will map itself to the
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* virtual address.
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*
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* We return the starting address. */
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static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr,
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unsigned long *page_offset)
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static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr)
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{
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void *start = (void *)-1, *end = NULL;
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Elf32_Phdr phdr[ehdr->e_phnum];
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@ -255,9 +249,6 @@ static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr,
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if (read(elf_fd, phdr, sizeof(phdr)) != sizeof(phdr))
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err(1, "Reading program headers");
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/* We don't know page_offset yet. */
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*page_offset = 0;
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/* Try all the headers: there are usually only three. A read-only one,
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* a read-write one, and a "note" section which isn't loadable. */
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for (i = 0; i < ehdr->e_phnum; i++) {
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@ -268,14 +259,6 @@ static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr,
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verbose("Section %i: size %i addr %p\n",
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i, phdr[i].p_memsz, (void *)phdr[i].p_paddr);
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/* We expect a simple linear address space: every segment must
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* have the same difference between virtual (p_vaddr) and
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* physical (p_paddr) address. */
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if (!*page_offset)
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*page_offset = phdr[i].p_vaddr - phdr[i].p_paddr;
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else if (*page_offset != phdr[i].p_vaddr - phdr[i].p_paddr)
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errx(1, "Page offset of section %i different", i);
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/* We track the first and last address we mapped, so we can
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* tell entry_point() where to scan. */
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if (from_guest_phys(phdr[i].p_paddr) < start)
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@ -288,50 +271,13 @@ static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr,
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phdr[i].p_offset, phdr[i].p_filesz);
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}
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return entry_point(start, end, *page_offset);
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}
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/*L:170 Prepare to be SHOCKED and AMAZED. And possibly a trifle nauseated.
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*
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* We know that CONFIG_PAGE_OFFSET sets what virtual address the kernel expects
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* to be. We don't know what that option was, but we can figure it out
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* approximately by looking at the addresses in the code. I chose the common
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* case of reading a memory location into the %eax register:
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*
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* movl <some-address>, %eax
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*
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* This gets encoded as five bytes: "0xA1 <4-byte-address>". For example,
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* "0xA1 0x18 0x60 0x47 0xC0" reads the address 0xC0476018 into %eax.
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*
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* In this example can guess that the kernel was compiled with
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* CONFIG_PAGE_OFFSET set to 0xC0000000 (it's always a round number). If the
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* kernel were larger than 16MB, we might see 0xC1 addresses show up, but our
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* kernel isn't that bloated yet.
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*
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* Unfortunately, x86 has variable-length instructions, so finding this
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* particular instruction properly involves writing a disassembler. Instead,
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* we rely on statistics. We look for "0xA1" and tally the different bytes
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* which occur 4 bytes later (the "0xC0" in our example above). When one of
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* those bytes appears three times, we can be reasonably confident that it
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* forms the start of CONFIG_PAGE_OFFSET.
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*
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* This is amazingly reliable. */
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static unsigned long intuit_page_offset(unsigned char *img, unsigned long len)
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{
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unsigned int i, possibilities[256] = { 0 };
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for (i = 0; i + 4 < len; i++) {
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/* mov 0xXXXXXXXX,%eax */
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if (img[i] == 0xA1 && ++possibilities[img[i+4]] > 3)
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return (unsigned long)img[i+4] << 24;
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}
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errx(1, "could not determine page offset");
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return entry_point(start, end);
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}
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/*L:160 Unfortunately the entire ELF image isn't compressed: the segments
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* which need loading are extracted and compressed raw. This denies us the
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* information we need to make a fully-general loader. */
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static unsigned long unpack_bzimage(int fd, unsigned long *page_offset)
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static unsigned long unpack_bzimage(int fd)
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{
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gzFile f;
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int ret, len = 0;
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@ -352,12 +298,7 @@ static unsigned long unpack_bzimage(int fd, unsigned long *page_offset)
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verbose("Unpacked size %i addr %p\n", len, img);
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/* Without the ELF header, we can't tell virtual-physical gap. This is
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* CONFIG_PAGE_OFFSET, and people do actually change it. Fortunately,
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* I have a clever way of figuring it out from the code itself. */
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*page_offset = intuit_page_offset(img, len);
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return entry_point(img, img + len, *page_offset);
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return entry_point(img, img + len);
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}
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/*L:150 A bzImage, unlike an ELF file, is not meant to be loaded. You're
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@ -368,7 +309,7 @@ static unsigned long unpack_bzimage(int fd, unsigned long *page_offset)
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* The bzImage is formed by putting the decompressing code in front of the
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* compressed kernel code. So we can simple scan through it looking for the
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* first "gzip" header, and start decompressing from there. */
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static unsigned long load_bzimage(int fd, unsigned long *page_offset)
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static unsigned long load_bzimage(int fd)
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{
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unsigned char c;
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int state = 0;
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@ -396,7 +337,7 @@ static unsigned long load_bzimage(int fd, unsigned long *page_offset)
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if (c != 0x03)
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state = -1;
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else
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return unpack_bzimage(fd, page_offset);
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return unpack_bzimage(fd);
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}
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}
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errx(1, "Could not find kernel in bzImage");
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@ -405,7 +346,7 @@ static unsigned long load_bzimage(int fd, unsigned long *page_offset)
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/*L:140 Loading the kernel is easy when it's a "vmlinux", but most kernels
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* come wrapped up in the self-decompressing "bzImage" format. With some funky
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* coding, we can load those, too. */
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static unsigned long load_kernel(int fd, unsigned long *page_offset)
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static unsigned long load_kernel(int fd)
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{
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Elf32_Ehdr hdr;
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@ -415,10 +356,10 @@ static unsigned long load_kernel(int fd, unsigned long *page_offset)
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/* If it's an ELF file, it starts with "\177ELF" */
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if (memcmp(hdr.e_ident, ELFMAG, SELFMAG) == 0)
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return map_elf(fd, &hdr, page_offset);
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return map_elf(fd, &hdr);
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/* Otherwise we assume it's a bzImage, and try to unpack it */
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return load_bzimage(fd, page_offset);
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return load_bzimage(fd);
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}
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/* This is a trivial little helper to align pages. Andi Kleen hated it because
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@ -463,27 +404,20 @@ static unsigned long load_initrd(const char *name, unsigned long mem)
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return len;
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}
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/* Once we know the address the Guest kernel expects, we can construct simple
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* linear page tables for all of memory which will get the Guest far enough
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/* Once we know how much memory we have, we can construct simple linear page
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* tables which set virtual == physical which will get the Guest far enough
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* into the boot to create its own.
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*
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* We lay them out of the way, just below the initrd (which is why we need to
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* know its size). */
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static unsigned long setup_pagetables(unsigned long mem,
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unsigned long initrd_size,
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unsigned long page_offset)
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unsigned long initrd_size)
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{
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unsigned long *pgdir, *linear;
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unsigned int mapped_pages, i, linear_pages;
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unsigned int ptes_per_page = getpagesize()/sizeof(void *);
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/* Ideally we map all physical memory starting at page_offset.
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* However, if page_offset is 0xC0000000 we can only map 1G of physical
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* (0xC0000000 + 1G overflows). */
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if (mem <= -page_offset)
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mapped_pages = mem/getpagesize();
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else
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mapped_pages = -page_offset/getpagesize();
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mapped_pages = mem/getpagesize();
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/* Each PTE page can map ptes_per_page pages: how many do we need? */
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linear_pages = (mapped_pages + ptes_per_page-1)/ptes_per_page;
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@ -500,11 +434,9 @@ static unsigned long setup_pagetables(unsigned long mem,
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for (i = 0; i < mapped_pages; i++)
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linear[i] = ((i * getpagesize()) | PAGE_PRESENT);
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/* The top level points to the linear page table pages above. The
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* entry representing page_offset points to the first one, and they
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* continue from there. */
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/* The top level points to the linear page table pages above. */
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for (i = 0; i < mapped_pages; i += ptes_per_page) {
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pgdir[(i + page_offset/getpagesize())/ptes_per_page]
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pgdir[i/ptes_per_page]
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= ((to_guest_phys(linear) + i*sizeof(void *))
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}
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@ -535,15 +467,12 @@ static void concat(char *dst, char *args[])
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/* This is where we actually tell the kernel to initialize the Guest. We saw
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* the arguments it expects when we looked at initialize() in lguest_user.c:
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* the base of guest "physical" memory, the top physical page to allow, the
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* top level pagetable, the entry point and the page_offset constant for the
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* Guest. */
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static int tell_kernel(unsigned long pgdir, unsigned long start,
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unsigned long page_offset)
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* top level pagetable and the entry point for the Guest. */
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static int tell_kernel(unsigned long pgdir, unsigned long start)
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{
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unsigned long args[] = { LHREQ_INITIALIZE,
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(unsigned long)guest_base,
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guest_limit / getpagesize(),
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pgdir, start, page_offset };
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guest_limit / getpagesize(), pgdir, start };
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int fd;
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verbose("Guest: %p - %p (%#lx)\n",
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@ -1424,9 +1353,9 @@ static void usage(void)
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/*L:105 The main routine is where the real work begins: */
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int main(int argc, char *argv[])
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{
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/* Memory, top-level pagetable, code startpoint, PAGE_OFFSET and size
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* of the (optional) initrd. */
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unsigned long mem = 0, pgdir, start, page_offset, initrd_size = 0;
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/* Memory, top-level pagetable, code startpoint and size of the
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* (optional) initrd. */
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unsigned long mem = 0, pgdir, start, initrd_size = 0;
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/* A temporary and the /dev/lguest file descriptor. */
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int i, c, lguest_fd;
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/* The list of Guest devices, based on command line arguments. */
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@ -1500,8 +1429,7 @@ int main(int argc, char *argv[])
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setup_console(&device_list);
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/* Now we load the kernel */
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start = load_kernel(open_or_die(argv[optind+1], O_RDONLY),
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&page_offset);
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start = load_kernel(open_or_die(argv[optind+1], O_RDONLY));
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/* Boot information is stashed at physical address 0 */
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boot = from_guest_phys(0);
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@ -1518,7 +1446,7 @@ int main(int argc, char *argv[])
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}
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/* Set up the initial linear pagetables, starting below the initrd. */
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pgdir = setup_pagetables(mem, initrd_size, page_offset);
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pgdir = setup_pagetables(mem, initrd_size);
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/* The Linux boot header contains an "E820" memory map: ours is a
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* simple, single region. */
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@ -1535,7 +1463,7 @@ int main(int argc, char *argv[])
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/* We tell the kernel to initialize the Guest: this returns the open
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* /dev/lguest file descriptor. */
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lguest_fd = tell_kernel(pgdir, start, page_offset);
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lguest_fd = tell_kernel(pgdir, start);
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/* We fork off a child process, which wakes the Launcher whenever one
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* of the input file descriptors needs attention. Otherwise we would
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