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s390/kvm: remove delayed reallocation of page tables for KVM 

Replacing a 2K page table with a 4K page table while a VMA is active
for the affected memory region is fundamentally broken. Rip out the
page table reallocation code and replace it with a simple system
control 'vm.allocate_pgste'. If the system control is set the page
tables for all processes are allocated as full 4K pages, even for
processes that do not need it.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky 2015-04-15 13:23:26 +02:00
parent 7e01b5acd8
commit 0b46e0a3ec
5 changed files with 59 additions and 100 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
arch/s390/include/asm/mmu.h
View File

@ -14,7 +14,9 @@ typedef struct {
unsigned long asce_bits;
unsigned long asce_limit;
unsigned long vdso_base;
/* The mmu context has extended page tables. */
/* The mmu context allocates 4K page tables. */
unsigned int alloc_pgste:1;
/* The mmu context uses extended page tables. */
unsigned int has_pgste:1;
/* The mmu context uses storage keys. */
unsigned int use_skey:1;

3
arch/s390/include/asm/mmu_context.h
View File

@ -20,8 +20,11 @@ static inline int init_new_context(struct task_struct *tsk,
mm->context.flush_mm = 0;
mm->context.asce_bits = _ASCE_TABLE_LENGTH | _ASCE_USER_BITS;
mm->context.asce_bits |= _ASCE_TYPE_REGION3;
#ifdef CONFIG_PGSTE
mm->context.alloc_pgste = page_table_allocate_pgste;
mm->context.has_pgste = 0;
mm->context.use_skey = 0;
#endif
mm->context.asce_limit = STACK_TOP_MAX;
crst_table_init((unsigned long *) mm->pgd, pgd_entry_type(mm));
return 0;

1
arch/s390/include/asm/pgalloc.h
View File

@ -21,6 +21,7 @@ void crst_table_free(struct mm_struct *, unsigned long *);
unsigned long *page_table_alloc(struct mm_struct *);
void page_table_free(struct mm_struct *, unsigned long *);
void page_table_free_rcu(struct mmu_gather *, unsigned long *, unsigned long);
extern int page_table_allocate_pgste;
int set_guest_storage_key(struct mm_struct *mm, unsigned long addr,
unsigned long key, bool nq);

9
arch/s390/include/asm/pgtable.h
View File

@ -423,6 +423,15 @@ static inline int mm_has_pgste(struct mm_struct *mm)
return 0;
}
static inline int mm_alloc_pgste(struct mm_struct *mm)
{
#ifdef CONFIG_PGSTE
if (unlikely(mm->context.alloc_pgste))
return 1;
#endif
return 0;
}
/*
* In the case that a guest uses storage keys
* faults should no longer be backed by zero pages

142
arch/s390/mm/pgtable.c
View File

@ -18,6 +18,7 @@
#include <linux/rcupdate.h>
#include <linux/slab.h>
#include <linux/swapops.h>
#include <linux/sysctl.h>
#include <linux/ksm.h>
#include <linux/mman.h>
@ -920,6 +921,40 @@ unsigned long get_guest_storage_key(struct mm_struct *mm, unsigned long addr)
}
EXPORT_SYMBOL(get_guest_storage_key);
static int page_table_allocate_pgste_min = 0;
static int page_table_allocate_pgste_max = 1;
int page_table_allocate_pgste = 0;
EXPORT_SYMBOL(page_table_allocate_pgste);
static struct ctl_table page_table_sysctl[] = {
{
.procname = "allocate_pgste",
.data = &page_table_allocate_pgste,
.maxlen = sizeof(int),
.mode = S_IRUGO | S_IWUSR,
.proc_handler = proc_dointvec,
.extra1 = &page_table_allocate_pgste_min,
.extra2 = &page_table_allocate_pgste_max,
},
{ }
};
static struct ctl_table page_table_sysctl_dir[] = {
{
.procname = "vm",
.maxlen = 0,
.mode = 0555,
.child = page_table_sysctl,
},
{ }
};
static int __init page_table_register_sysctl(void)
{
return register_sysctl_table(page_table_sysctl_dir) ? 0 : -ENOMEM;
}
__initcall(page_table_register_sysctl);
#else /* CONFIG_PGSTE */
static inline int page_table_with_pgste(struct page *page)
@ -963,7 +998,7 @@ unsigned long *page_table_alloc(struct mm_struct *mm)
struct page *uninitialized_var(page);
unsigned int mask, bit;
if (mm_has_pgste(mm))
if (mm_alloc_pgste(mm))
return page_table_alloc_pgste(mm);
/* Allocate fragments of a 4K page as 1K/2K page table */
spin_lock_bh(&mm->context.list_lock);
@ -1165,116 +1200,25 @@ static inline void thp_split_mm(struct mm_struct *mm)
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
static unsigned long page_table_realloc_pmd(struct mmu_gather *tlb,
struct mm_struct *mm, pud_t *pud,
unsigned long addr, unsigned long end)
{
unsigned long next, *table, *new;
struct page *page;
spinlock_t *ptl;
pmd_t *pmd;
pmd = pmd_offset(pud, addr);
do {
next = pmd_addr_end(addr, end);
again:
if (pmd_none_or_clear_bad(pmd))
continue;
table = (unsigned long *) pmd_deref(*pmd);
page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
if (page_table_with_pgste(page))
continue;
/* Allocate new page table with pgstes */
new = page_table_alloc_pgste(mm);
if (!new)
return -ENOMEM;
ptl = pmd_lock(mm, pmd);
if (likely((unsigned long *) pmd_deref(*pmd) == table)) {
/* Nuke pmd entry pointing to the "short" page table */
pmdp_flush_lazy(mm, addr, pmd);
pmd_clear(pmd);
/* Copy ptes from old table to new table */
memcpy(new, table, PAGE_SIZE/2);
clear_table(table, _PAGE_INVALID, PAGE_SIZE/2);
/* Establish new table */
pmd_populate(mm, pmd, (pte_t *) new);
/* Free old table with rcu, there might be a walker! */
page_table_free_rcu(tlb, table, addr);
new = NULL;
}
spin_unlock(ptl);
if (new) {
page_table_free_pgste(new);
goto again;
}
} while (pmd++, addr = next, addr != end);
return addr;
}
static unsigned long page_table_realloc_pud(struct mmu_gather *tlb,
struct mm_struct *mm, pgd_t *pgd,
unsigned long addr, unsigned long end)
{
unsigned long next;
pud_t *pud;
pud = pud_offset(pgd, addr);
do {
next = pud_addr_end(addr, end);
if (pud_none_or_clear_bad(pud))
continue;
next = page_table_realloc_pmd(tlb, mm, pud, addr, next);
if (unlikely(IS_ERR_VALUE(next)))
return next;
} while (pud++, addr = next, addr != end);
return addr;
}
static unsigned long page_table_realloc(struct mmu_gather *tlb, struct mm_struct *mm,
unsigned long addr, unsigned long end)
{
unsigned long next;
pgd_t *pgd;
pgd = pgd_offset(mm, addr);
do {
next = pgd_addr_end(addr, end);
if (pgd_none_or_clear_bad(pgd))
continue;
next = page_table_realloc_pud(tlb, mm, pgd, addr, next);
if (unlikely(IS_ERR_VALUE(next)))
return next;
} while (pgd++, addr = next, addr != end);
return 0;
}
/*
* switch on pgstes for its userspace process (for kvm)
*/
int s390_enable_sie(void)
{
struct task_struct *tsk = current;
struct mm_struct *mm = tsk->mm;
struct mmu_gather tlb;
struct mm_struct *mm = current->mm;
/* Do we have pgstes? if yes, we are done */
if (mm_has_pgste(tsk->mm))
if (mm_has_pgste(mm))
return 0;
/* Fail if the page tables are 2K */
if (!mm_alloc_pgste(mm))
return -EINVAL;
down_write(&mm->mmap_sem);
mm->context.has_pgste = 1;
/* split thp mappings and disable thp for future mappings */
thp_split_mm(mm);
/* Reallocate the page tables with pgstes */
tlb_gather_mmu(&tlb, mm, 0, TASK_SIZE);
if (!page_table_realloc(&tlb, mm, 0, TASK_SIZE))
mm->context.has_pgste = 1;
tlb_finish_mmu(&tlb, 0, TASK_SIZE);
up_write(&mm->mmap_sem);
return mm->context.has_pgste ? 0 : -ENOMEM;
return 0;
}
EXPORT_SYMBOL_GPL(s390_enable_sie);