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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>
This commit is contained in:
Heiko Carstens 2017-04-24 15:27:35 +02:00 committed by Martin Schwidefsky
parent 9b11c7912d
commit 1366def38b
1 changed files with 7 additions and 3 deletions
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10
arch/s390/mm/pageattr.c
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@ -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);
}