Re: [RFC:PATCH 02/06] mm: Allow architectures to define additional protection bits

On Tue, 2008-06-10 at 15:14 -0700, Andrew Morton wrote:

On Tue, 10 Jun 2008 18:01:07 -0400
Dave Kleikamp [off-list ref] wrote:

quoted

mm: Allow architectures to define additional protection bits

This patch allows architectures to define functions to deal with
additional protections bits for mmap() and mprotect().

arch_calc_vm_prot_bits() maps additonal protection bits to vm_flags
arch_vm_get_page_prot() maps additional vm_flags to the vma's vm_page_prot
arch_validate_prot() checks for valid values of the protection bits

Note: vm_get_page_prot() is now pretty ugly.  Suggestions?

It didn't get any better, no ;)

I wonder if we can do the ORing after doing the protection_map[]
lookup.  I guess that's illogical even if it happens to work.

I guess we can live with it.  Just holding out hope that someone might
see a nicer way to do it.

quoted

diff -Nurp linux001/include/linux/mman.h linux002/include/linux/mman.h

--- linux001/include/linux/mman.h	2008-06-05 10:08:01.000000000 -0500
+++ linux002/include/linux/mman.h	2008-06-10 16:48:59.000000000 -0500

@@ -34,6 +34,26 @@ static inline void vm_unacct_memory(long
 }
 
 /*
+ * Allow architectures to handle additional protection bits
+ */
+
+#ifndef HAVE_ARCH_PROT_BITS
+#define arch_calc_vm_prot_bits(prot) 0
+#define arch_vm_get_page_prot(vm_flags) __pgprot(0)
+
+/*
+ * This is called from mprotect().  PROT_GROWSDOWN and PROT_GROWSUP have
+ * already been masked out.
+ *
+ * Returns true if the prot flags are valid
+ */
+static inline int arch_validate_prot(unsigned long prot)
+{
+	return (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM)) == 0;
+}
+#endif /* HAVE_ARCH_PROT_BITS */

argh, another HAVE_ARCH_foo.

Sorry.  I didn't realize HAVE_ARCH_foo was so evil.

A good (but verbose) way of doing this is to nuke the ifdefs and just
go and define these three things for each architecture.  That can be
done via copy-n-paste into include/asm-*/mman.h or #include
<asm-generic/arch-mman.h>(?) within each asm/mman.h.

Another way would be

#ifndef arch_calc_vm_prot_bits
#define arch_calc_vm_prot_bits(prot) ...

I think I prefer this method.  I'll get rid of HAVE_ARCH_PROT_BITS.

Thanks,
Shaggy
-- 
David Kleikamp
IBM Linux Technology Center