Re: GIT head no longer boots on x86-64

Linus Torvalds
2008-10-15T15:36:22Z

On Wed, 15 Oct 2008, Linus Torvalds wrote:
>
> The code in question already does
>
> VIRTUAL_BUG_ON(!is_vmalloc_addr(vmalloc_addr) &&
> !is_module_address(addr));
>
> and look at that thing and ask yourself: where was the bug again.

Btw, I don't even know if this is a sparc64 issue too, but it sounds
possible. Sparc64 seems similar to x86-64 in that there is a special range
for module addresses.

I'm too lazy to check everybody's "module_alloc()", and maybe others do
too, but use a different symbol, so grepping for it doesn't trigger.

But regardless, a much more correct fix appears to just screw this, and
make it explicit on the symbol. And only do it if modules are even
supported.

And if you *really* want to change "is_vmalloc_addr()", then

(a) do it right, not some crappy x86-64-specific sh*t
(b) do it like I do it, and make it dependent on modules even being
enabled
(c) and rename it to match what it does.

not the horrible patch I've seen.

Oh, btw. This patch is *totally* untested. I don't even enable modules. So
if it doesn't compile, it isn't perfect. But while it may not _work_, at
least it's not _ugly_.

(Quite frankly, I think an even more correct fix is to rename the whole
"vmalloc_to_page()" function, since it's clearly used for other things
than vmalloc. Maybe "kernel_virtual_to_page()". Whatever. This is trying
to be minimal without being totally disgusting).

Linus

---
mm/vmalloc.c | 18 ++++++++++++++++--
1 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index bba06c4..f018d7e 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -168,6 +168,21 @@ int map_vm_area(struct vm_struct *area, pgprot_t prot, struct page ***pages)
}
EXPORT_SYMBOL_GPL(map_vm_area);

+static inline int is_vmalloc_or_module_addr(const void *x)
+{
+ /*
+ * x86-64 and sparc64 put modules in a special place,
+ * and fall back on vmalloc() if that fails. Others
+ * just put it in the vmalloc space.
+ */
+#if defined(CONFIG_MODULES) && defined(MODULES_VADDR)
+ unsigned long addr = (unsigned long)x;
+ if (addr >= MODULES_VADDR && addr < MODULES_END)
+ return 1;
+#endif
+ return is_vmalloc_addr(x);
+}
+
/*
* Map a vmalloc()-space virtual address to the physical page.
*/
@@ -184,8 +199,7 @@ struct page *vmalloc_to_page(const void *vmalloc_addr)
* XXX we might need to change this if we add VIRTUAL_BUG_ON for
* architectures that do not vmalloc module space
*/
- VIRTUAL_BUG_ON(!is_vmalloc_addr(vmalloc_addr) &&
- !is_module_address(addr));
+ VIRTUAL_BUG_ON(!is_vmalloc_or_module_addr(vmalloc_addr));

if (!pgd_none(*pgd)) {
pud = pud_offset(pgd, addr);