s390/pageattr: avoid unnecessary page table splitting

The kernel page table splitting code will split page tables even for
features the CPU does not support. E.g. a CPU may not support the NX
feature.
In order to avoid this, remove those bits from the flags parameter
that correlate with unsupported CPU features within __set_memory(). In
addition add an early exit if the flags parameter does not have any
bits set afterwards.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/mm/pageattr.c b/arch/s390/mm/pageattr.c
index fc5dc33bb141798a9ed6c4f31762841653e096e1..fc321c5ec30e0c91bd035e4848db2aef3875a00c 100644 (file)
--- a/arch/s390/mm/pageattr.c
+++ b/arch/s390/mm/pageattr.c
@@ -94,7 +94,7 @@ static int walk_pte_level(pmd_t *pmdp, unsigned long addr, unsigned long end,
                        new = pte_wrprotect(new);
                else if (flags & SET_MEMORY_RW)
                        new = pte_mkwrite(pte_mkdirty(new));
-               if ((flags & SET_MEMORY_NX) && MACHINE_HAS_NX)
+               if (flags & SET_MEMORY_NX)
                        pte_val(new) |= _PAGE_NOEXEC;
                else if (flags & SET_MEMORY_X)
                        pte_val(new) &= ~_PAGE_NOEXEC;
@@ -144,7 +144,7 @@ static void modify_pmd_page(pmd_t *pmdp, unsigned long addr,
                new = pmd_wrprotect(new);
        else if (flags & SET_MEMORY_RW)
                new = pmd_mkwrite(pmd_mkdirty(new));
-       if ((flags & SET_MEMORY_NX) && MACHINE_HAS_NX)
+       if (flags & SET_MEMORY_NX)
                pmd_val(new) |= _SEGMENT_ENTRY_NOEXEC;
        else if (flags & SET_MEMORY_X)
                pmd_val(new) &= ~_SEGMENT_ENTRY_NOEXEC;
@@ -221,7 +221,7 @@ static void modify_pud_page(pud_t *pudp, unsigned long addr,
                new = pud_wrprotect(new);
        else if (flags & SET_MEMORY_RW)
                new = pud_mkwrite(pud_mkdirty(new));
-       if ((flags & SET_MEMORY_NX) && MACHINE_HAS_NX)
+       if (flags & SET_MEMORY_NX)
                pud_val(new) |= _REGION_ENTRY_NOEXEC;
        else if (flags & SET_MEMORY_X)
                pud_val(new) &= ~_REGION_ENTRY_NOEXEC;
@@ -288,6 +288,10 @@ static int change_page_attr(unsigned long addr, unsigned long end,
 
 int __set_memory(unsigned long addr, int numpages, unsigned long flags)
 {
+       if (!MACHINE_HAS_NX)
+               flags &= ~(SET_MEMORY_NX | SET_MEMORY_X);
+       if (!flags)
+               return 0;
        addr &= PAGE_MASK;
        return change_page_attr(addr, addr + numpages * PAGE_SIZE, flags);
 }