x86, nx: Don't force pages RW when setting NX bits

Xen want page table pages read only.

But the initial page table (from head_*.S) live in .data or .bss.

That was broken by 64edc8ed5ffae999d8d413ba006850e9e34166cb.  There is
absolutely no reason to force these pages RW after they have already
been marked RO.

Signed-off-by: Matthieu CASTET <castet.matthieu@free.fr>
Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 8b830ca..d343b3c 100644 (file)
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -256,7 +256,6 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long address,
                                   unsigned long pfn)
 {
        pgprot_t forbidden = __pgprot(0);
-       pgprot_t required = __pgprot(0);
 
        /*
         * The BIOS area between 640k and 1Mb needs to be executable for
@@ -282,12 +281,6 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long address,
        if (within(pfn, __pa((unsigned long)__start_rodata) >> PAGE_SHIFT,
                   __pa((unsigned long)__end_rodata) >> PAGE_SHIFT))
                pgprot_val(forbidden) |= _PAGE_RW;
-       /*
-        * .data and .bss should always be writable.
-        */
-       if (within(address, (unsigned long)_sdata, (unsigned long)_edata) ||
-           within(address, (unsigned long)__bss_start, (unsigned long)__bss_stop))
-               pgprot_val(required) |= _PAGE_RW;
 
 #if defined(CONFIG_X86_64) && defined(CONFIG_DEBUG_RODATA)
        /*
@@ -327,7 +320,6 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long address,
 #endif
 
        prot = __pgprot(pgprot_val(prot) & ~pgprot_val(forbidden));
-       prot = __pgprot(pgprot_val(prot) | pgprot_val(required));
 
        return prot;
 }