[PATCH] lguest: don't use paravirt_probe, it's dying

Rusty Russell
2007-05-05T15:33:44Z

On Sat, 2007-05-05 at 13:22 +1000, Rusty Russell wrote:
> On Fri, 2007-05-04 at 20:53 -0600, Eric W. Biederman wrote:
> > Frankly I think the least risk of problems comes from just doing a
> > separate entry point for lguest for now. It means we don't even have
> > to touch the common code path and later dropping will be trivially
> > lguest specific, and certain to not break anything else.
>
> Hmm, I railed for so long against Xen doing that, it feels... wrong...
> to do that now 8)

And here's the patch. It's pretty trivial actually. It even worked
first time. It applies against -mm (ie. before the "boot with P=V"
patches I showed before).

Thanks!
Rusty.
==
paravirt_probe() and its infrastructure proved as popular as it was
pretty. In anticipation of its imminent demise, this switches lguest to
use a magic string to identify a different entry point.

This is not the long-term solution: that will take a new bootloader rev
and will hopefully be done in the next few months.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff -r 9cfbf629088e Documentation/lguest/lguest.c
--- a/Documentation/lguest/lguest.c Sat May 05 13:06:53 2007 +1000
+++ b/Documentation/lguest/lguest.c Sat May 05 17:33:25 2007 +1000
@@ -96,6 +96,19 @@ static void *map_zeroed_pages(unsigned l
return (void *)addr;
}

+/* Find magic string marking entry point, return entry point. */
+static unsigned long entry_point(void *start, void *end,
+ unsigned long page_offset)
+{
+ void *p;
+
+ for (p = start; p < end; p++)
+ if (memcmp(p, "GenuineLguest", strlen("GenuineLguest")) == 0)
+ return (long)p + strlen("GenuineLguest") + page_offset;
+
+ err(1, "Is this image a genuine lguest?");
+}
+
/* Returns the entry point */
static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr,
unsigned long *page_offset)
@@ -103,6 +116,7 @@ static unsigned long map_elf(int elf_fd,
void *addr;
Elf32_Phdr phdr[ehdr->e_phnum];
unsigned int i;
+ unsigned long start = -1UL, end = 0;

/* Sanity checks. */
if (ehdr->e_type != ET_EXEC
@@ -131,6 +145,11 @@ static unsigned long map_elf(int elf_fd,
*page_offset = phdr[i].p_vaddr - phdr[i].p_paddr;
else if (*page_offset != phdr[i].p_vaddr - phdr[i].p_paddr)
errx(1, "Page offset of section %i different", i);
+
+ if (phdr[i].p_paddr < start)
+ start = phdr[i].p_paddr;
+ if (phdr[i].p_paddr + phdr[i].p_filesz > end)
+ end = phdr[i].p_paddr + phdr[i].p_filesz;

/* We map everything private, writable. */
addr = mmap((void *)phdr[i].p_paddr,
@@ -143,8 +162,7 @@ static unsigned long map_elf(int elf_fd,
i, addr, (void *)phdr[i].p_paddr);
}

- /* Entry is physical address: convert to virtual */
- return ehdr->e_entry + *page_offset;
+ return entry_point((void *)start, (void *)end, *page_offset);
}

/* This is amazingly reliable. */
@@ -175,8 +193,7 @@ static unsigned long unpack_bzimage(int
verbose("Unpacked size %i addr %p\n", len, img);
*page_offset = intuit_page_offset(img, len);

- /* Entry is physical address: convert to virtual */
- return (unsigned long)img + *page_offset;
+ return entry_point(img, img + len, *page_offset);
}

static unsigned long load_bzimage(int fd, unsigned long *page_offset)
diff -r 9cfbf629088e drivers/lguest/lguest.c
--- a/drivers/lguest/lguest.c Sat May 05 13:06:53 2007 +1000
+++ b/drivers/lguest/lguest.c Sat May 05 17:21:44 2007 +1000
@@ -43,7 +43,6 @@ extern const char lgstart_popf[], lgend_
extern const char lgstart_popf[], lgend_popf[];
extern const char lgstart_pushf[], lgend_pushf[];
extern const char lgstart_iret[], lgend_iret[];
-extern asmlinkage void lguest_maybe_init(void);
extern void lguest_iret(void);

struct lguest_data lguest_data = {
@@ -497,4 +496,3 @@ __init void lguest_init(void)
pm_power_off = lguest_power_off;
start_kernel();
}
-paravirt_probe(lguest_maybe_init);
diff -r 9cfbf629088e drivers/lguest/lguest_asm.S
--- a/drivers/lguest/lguest_asm.S Sat May 05 13:06:53 2007 +1000
+++ b/drivers/lguest/lguest_asm.S Sat May 05 17:21:38 2007 +1000
@@ -1,29 +1,24 @@
#include <linux/linkage.h>
#include <linux/lguest.h>
#include <asm/asm-offsets.h>
+#include <asm/thread_info.h>

/* FIXME: Once asm/processor-flags.h goes in, include that */
#define X86_EFLAGS_IF 0x00000200

/*
- * This is where we begin: head.S notes that paging is already enabled (which
- * doesn't happen in native boot) and calls the registered paravirt_probe
- * functions one at a time. Ours is a simple assembler test for magic
- * registers. If they're correct we jump to lguest_init.
+ * This is where we begin: we have a magic signature which the launcher looks
+ * for. The plan is that the Linux boot protocol will be extended with a
+ * "platform type" field which will guide us here from the normal entry point,
+ * but for the moment this suffices.
*
* We put it in .init.text will be discarded after boot.
*/
.section .init.text, "ax", @progbits
-ENTRY(lguest_maybe_init)
- cmpl $LGUEST_MAGIC_EBP, %ebp
- jne out
- cmpl $LGUEST_MAGIC_EDI, %edi
- jne out
- cmpl $LGUEST_MAGIC_ESI, %esi
- jne out
- je lguest_init
-out:
- ret
+.ascii "GenuineLguest"
+ /* Set up initial stack. */
+ movl $(init_thread_union+THREAD_SIZE),%esp
+ jmp lguest_init

/* The templates for inline patching. */
#define LGUEST_PATCH(name, insns...) \