linux/arch/powerpc/mm/pgtable.c
Benjamin Herrenschmidt ea3cc330ac powerpc/mm: Cleanup handling of execute permission
This is an attempt at cleaning up a bit the way we handle execute
permission on powerpc. _PAGE_HWEXEC is gone, _PAGE_EXEC is now only
defined by CPUs that can do something with it, and the myriad of
#ifdef's in the I$/D$ coherency code is reduced to 2 cases that
hopefully should cover everything.

The logic on BookE is a little bit different than what it was though
not by much. Since now, _PAGE_EXEC will be set by the generic code
for executable pages, we need to filter out if they are unclean and
recover it. However, I don't expect the code to be more bloated than
it already was in that area due to that change.

I could boast that this brings proper enforcing of per-page execute
permissions to all BookE and 40x but in fact, we've had that now for
some time as a side effect of my previous rework in that area (and
I didn't even know it :-) We would only enable execute permission if
the page was cache clean and we would only cache clean it if we took
and exec fault. Since we now enforce that the later only work if
VM_EXEC is part of the VMA flags, we de-fact already enforce per-page
execute permissions... Unless I missed something

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
2009-08-27 13:12:51 +10:00

326 lines
8.5 KiB
C

/*
* This file contains common routines for dealing with free of page tables
* Along with common page table handling code
*
* Derived from arch/powerpc/mm/tlb_64.c:
* Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
*
* Modifications by Paul Mackerras (PowerMac) (paulus@cs.anu.edu.au)
* and Cort Dougan (PReP) (cort@cs.nmt.edu)
* Copyright (C) 1996 Paul Mackerras
*
* Derived from "arch/i386/mm/init.c"
* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
*
* Dave Engebretsen <engebret@us.ibm.com>
* Rework for PPC64 port.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/init.h>
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
#include <asm/tlb.h>
DEFINE_PER_CPU(struct mmu_gather, mmu_gathers);
#ifdef CONFIG_SMP
/*
* Handle batching of page table freeing on SMP. Page tables are
* queued up and send to be freed later by RCU in order to avoid
* freeing a page table page that is being walked without locks
*/
static DEFINE_PER_CPU(struct pte_freelist_batch *, pte_freelist_cur);
static unsigned long pte_freelist_forced_free;
struct pte_freelist_batch
{
struct rcu_head rcu;
unsigned int index;
pgtable_free_t tables[0];
};
#define PTE_FREELIST_SIZE \
((PAGE_SIZE - sizeof(struct pte_freelist_batch)) \
/ sizeof(pgtable_free_t))
static void pte_free_smp_sync(void *arg)
{
/* Do nothing, just ensure we sync with all CPUs */
}
/* This is only called when we are critically out of memory
* (and fail to get a page in pte_free_tlb).
*/
static void pgtable_free_now(pgtable_free_t pgf)
{
pte_freelist_forced_free++;
smp_call_function(pte_free_smp_sync, NULL, 1);
pgtable_free(pgf);
}
static void pte_free_rcu_callback(struct rcu_head *head)
{
struct pte_freelist_batch *batch =
container_of(head, struct pte_freelist_batch, rcu);
unsigned int i;
for (i = 0; i < batch->index; i++)
pgtable_free(batch->tables[i]);
free_page((unsigned long)batch);
}
static void pte_free_submit(struct pte_freelist_batch *batch)
{
INIT_RCU_HEAD(&batch->rcu);
call_rcu(&batch->rcu, pte_free_rcu_callback);
}
void pgtable_free_tlb(struct mmu_gather *tlb, pgtable_free_t pgf)
{
/* This is safe since tlb_gather_mmu has disabled preemption */
struct pte_freelist_batch **batchp = &__get_cpu_var(pte_freelist_cur);
if (atomic_read(&tlb->mm->mm_users) < 2 ||
cpumask_equal(mm_cpumask(tlb->mm), cpumask_of(smp_processor_id()))){
pgtable_free(pgf);
return;
}
if (*batchp == NULL) {
*batchp = (struct pte_freelist_batch *)__get_free_page(GFP_ATOMIC);
if (*batchp == NULL) {
pgtable_free_now(pgf);
return;
}
(*batchp)->index = 0;
}
(*batchp)->tables[(*batchp)->index++] = pgf;
if ((*batchp)->index == PTE_FREELIST_SIZE) {
pte_free_submit(*batchp);
*batchp = NULL;
}
}
void pte_free_finish(void)
{
/* This is safe since tlb_gather_mmu has disabled preemption */
struct pte_freelist_batch **batchp = &__get_cpu_var(pte_freelist_cur);
if (*batchp == NULL)
return;
pte_free_submit(*batchp);
*batchp = NULL;
}
#endif /* CONFIG_SMP */
static inline int is_exec_fault(void)
{
return current->thread.regs && TRAP(current->thread.regs) == 0x400;
}
/* We only try to do i/d cache coherency on stuff that looks like
* reasonably "normal" PTEs. We currently require a PTE to be present
* and we avoid _PAGE_SPECIAL and _PAGE_NO_CACHE. We also only do that
* on userspace PTEs
*/
static inline int pte_looks_normal(pte_t pte)
{
return (pte_val(pte) &
(_PAGE_PRESENT | _PAGE_SPECIAL | _PAGE_NO_CACHE | _PAGE_USER)) ==
(_PAGE_PRESENT | _PAGE_USER);
}
struct page * maybe_pte_to_page(pte_t pte)
{
unsigned long pfn = pte_pfn(pte);
struct page *page;
if (unlikely(!pfn_valid(pfn)))
return NULL;
page = pfn_to_page(pfn);
if (PageReserved(page))
return NULL;
return page;
}
#if defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0
/* Server-style MMU handles coherency when hashing if HW exec permission
* is supposed per page (currently 64-bit only). If not, then, we always
* flush the cache for valid PTEs in set_pte. Embedded CPU without HW exec
* support falls into the same category.
*/
static pte_t set_pte_filter(pte_t pte)
{
pte = __pte(pte_val(pte) & ~_PAGE_HPTEFLAGS);
if (pte_looks_normal(pte) && !(cpu_has_feature(CPU_FTR_COHERENT_ICACHE) ||
cpu_has_feature(CPU_FTR_NOEXECUTE))) {
struct page *pg = maybe_pte_to_page(pte);
if (!pg)
return pte;
if (!test_bit(PG_arch_1, &pg->flags)) {
flush_dcache_icache_page(pg);
set_bit(PG_arch_1, &pg->flags);
}
}
return pte;
}
static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
int dirty)
{
return pte;
}
#else /* defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0 */
/* Embedded type MMU with HW exec support. This is a bit more complicated
* as we don't have two bits to spare for _PAGE_EXEC and _PAGE_HWEXEC so
* instead we "filter out" the exec permission for non clean pages.
*/
static pte_t set_pte_filter(pte_t pte)
{
struct page *pg;
/* No exec permission in the first place, move on */
if (!(pte_val(pte) & _PAGE_EXEC) || !pte_looks_normal(pte))
return pte;
/* If you set _PAGE_EXEC on weird pages you're on your own */
pg = maybe_pte_to_page(pte);
if (unlikely(!pg))
return pte;
/* If the page clean, we move on */
if (test_bit(PG_arch_1, &pg->flags))
return pte;
/* If it's an exec fault, we flush the cache and make it clean */
if (is_exec_fault()) {
flush_dcache_icache_page(pg);
set_bit(PG_arch_1, &pg->flags);
return pte;
}
/* Else, we filter out _PAGE_EXEC */
return __pte(pte_val(pte) & ~_PAGE_EXEC);
}
static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
int dirty)
{
struct page *pg;
/* So here, we only care about exec faults, as we use them
* to recover lost _PAGE_EXEC and perform I$/D$ coherency
* if necessary. Also if _PAGE_EXEC is already set, same deal,
* we just bail out
*/
if (dirty || (pte_val(pte) & _PAGE_EXEC) || !is_exec_fault())
return pte;
#ifdef CONFIG_DEBUG_VM
/* So this is an exec fault, _PAGE_EXEC is not set. If it was
* an error we would have bailed out earlier in do_page_fault()
* but let's make sure of it
*/
if (WARN_ON(!(vma->vm_flags & VM_EXEC)))
return pte;
#endif /* CONFIG_DEBUG_VM */
/* If you set _PAGE_EXEC on weird pages you're on your own */
pg = maybe_pte_to_page(pte);
if (unlikely(!pg))
goto bail;
/* If the page is already clean, we move on */
if (test_bit(PG_arch_1, &pg->flags))
goto bail;
/* Clean the page and set PG_arch_1 */
flush_dcache_icache_page(pg);
set_bit(PG_arch_1, &pg->flags);
bail:
return __pte(pte_val(pte) | _PAGE_EXEC);
}
#endif /* !(defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0) */
/*
* set_pte stores a linux PTE into the linux page table.
*/
void set_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep,
pte_t pte)
{
#ifdef CONFIG_DEBUG_VM
WARN_ON(pte_present(*ptep));
#endif
/* Note: mm->context.id might not yet have been assigned as
* this context might not have been activated yet when this
* is called.
*/
pte = set_pte_filter(pte);
/* Perform the setting of the PTE */
__set_pte_at(mm, addr, ptep, pte, 0);
}
/*
* This is called when relaxing access to a PTE. It's also called in the page
* fault path when we don't hit any of the major fault cases, ie, a minor
* update of _PAGE_ACCESSED, _PAGE_DIRTY, etc... The generic code will have
* handled those two for us, we additionally deal with missing execute
* permission here on some processors
*/
int ptep_set_access_flags(struct vm_area_struct *vma, unsigned long address,
pte_t *ptep, pte_t entry, int dirty)
{
int changed;
entry = set_access_flags_filter(entry, vma, dirty);
changed = !pte_same(*(ptep), entry);
if (changed) {
if (!(vma->vm_flags & VM_HUGETLB))
assert_pte_locked(vma->vm_mm, address);
__ptep_set_access_flags(ptep, entry);
flush_tlb_page_nohash(vma, address);
}
return changed;
}
#ifdef CONFIG_DEBUG_VM
void assert_pte_locked(struct mm_struct *mm, unsigned long addr)
{
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;
if (mm == &init_mm)
return;
pgd = mm->pgd + pgd_index(addr);
BUG_ON(pgd_none(*pgd));
pud = pud_offset(pgd, addr);
BUG_ON(pud_none(*pud));
pmd = pmd_offset(pud, addr);
BUG_ON(!pmd_present(*pmd));
assert_spin_locked(pte_lockptr(mm, pmd));
}
#endif /* CONFIG_DEBUG_VM */