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Commit 402b0862 authored by Carsten Otte's avatar Carsten Otte Committed by Avi Kivity
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s390: KVM preparation: provide hook to enable pgstes in user pagetable 



The SIE instruction on s390 uses the 2nd half of the page table page to
virtualize the storage keys of a guest. This patch offers the s390_enable_sie
function, which reorganizes the page tables of a single-threaded process to
reserve space in the page table:
s390_enable_sie makes sure that the process is single threaded and then uses
dup_mm to create a new mm with reorganized page tables. The old mm is freed
and the process has now a page status extended field after every page table.

Code that wants to exploit pgstes should SELECT CONFIG_PGSTE.

This patch has a small common code hit, namely making dup_mm non-static.

Edit (Carsten): I've modified Martin's patch, following Jeremy Fitzhardinge's
review feedback. Now we do have the prototype for dup_mm in
include/linux/sched.h. Following Martin's suggestion, s390_enable_sie() does now
call task_lock() to prevent race against ptrace modification of mm_users.

Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: default avatarCarsten Otte <cotte@de.ibm.com>
Acked-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarAvi Kivity <avi@qumranet.com>
parent 37817f29

arch/s390/Kconfig

+4 −0
Original line number Diff line number Diff line
@@ -62,6 +62,10 @@ config GENERIC_LOCKBREAK 
	default y

	depends on SMP && PREEMPT



config PGSTE

	bool

	default y if KVM



mainmenu "Linux Kernel Configuration"



config S390

arch/s390/kernel/setup.c

+4 −0
Original line number Diff line number Diff line
@@ -316,7 +316,11 @@ static int __init early_parse_ipldelay(char *p) 
early_param("ipldelay", early_parse_ipldelay);



#ifdef CONFIG_S390_SWITCH_AMODE

#ifdef CONFIG_PGSTE

unsigned int switch_amode = 1;

#else

unsigned int switch_amode = 0;

#endif

EXPORT_SYMBOL_GPL(switch_amode);



static void set_amode_and_uaccess(unsigned long user_amode,

arch/s390/mm/pgtable.c

+62 −3
Original line number Diff line number Diff line
@@ -30,11 +30,27 @@ 
#define TABLES_PER_PAGE	4

#define FRAG_MASK	15UL

#define SECOND_HALVES	10UL



void clear_table_pgstes(unsigned long *table)

{

	clear_table(table, _PAGE_TYPE_EMPTY, PAGE_SIZE/4);

	memset(table + 256, 0, PAGE_SIZE/4);

	clear_table(table + 512, _PAGE_TYPE_EMPTY, PAGE_SIZE/4);

	memset(table + 768, 0, PAGE_SIZE/4);

}



#else

#define ALLOC_ORDER	2

#define TABLES_PER_PAGE	2

#define FRAG_MASK	3UL

#define SECOND_HALVES	2UL



void clear_table_pgstes(unsigned long *table)

{

	clear_table(table, _PAGE_TYPE_EMPTY, PAGE_SIZE/2);

	memset(table + 256, 0, PAGE_SIZE/2);

}



#endif



unsigned long *crst_table_alloc(struct mm_struct *mm, int noexec)
@@ -153,7 +169,7 @@ unsigned long *page_table_alloc(struct mm_struct *mm) 
	unsigned long *table;

	unsigned long bits;



	bits = mm->context.noexec ? 3UL : 1UL;

	bits = (mm->context.noexec || mm->context.pgstes) ? 3UL : 1UL;

	spin_lock(&mm->page_table_lock);

	page = NULL;

	if (!list_empty(&mm->context.pgtable_list)) {
@@ -170,6 +186,9 @@ unsigned long *page_table_alloc(struct mm_struct *mm) 
		pgtable_page_ctor(page);

		page->flags &= ~FRAG_MASK;

		table = (unsigned long *) page_to_phys(page);

		if (mm->context.pgstes)

			clear_table_pgstes(table);

		else

			clear_table(table, _PAGE_TYPE_EMPTY, PAGE_SIZE);

		spin_lock(&mm->page_table_lock);

		list_add(&page->lru, &mm->context.pgtable_list);
@@ -191,7 +210,7 @@ void page_table_free(struct mm_struct *mm, unsigned long *table) 
	struct page *page;

	unsigned long bits;



	bits = mm->context.noexec ? 3UL : 1UL;

	bits = (mm->context.noexec || mm->context.pgstes) ? 3UL : 1UL;

	bits <<= (__pa(table) & (PAGE_SIZE - 1)) / 256 / sizeof(unsigned long);

	page = pfn_to_page(__pa(table) >> PAGE_SHIFT);

	spin_lock(&mm->page_table_lock);
@@ -228,3 +247,43 @@ void disable_noexec(struct mm_struct *mm, struct task_struct *tsk) 
	mm->context.noexec = 0;

	update_mm(mm, tsk);

}



/*

 * switch on pgstes for its userspace process (for kvm)

 */

int s390_enable_sie(void)

{

	struct task_struct *tsk = current;

	struct mm_struct *mm;

	int rc;



	task_lock(tsk);



	rc = 0;

	if (tsk->mm->context.pgstes)

		goto unlock;



	rc = -EINVAL;

	if (!tsk->mm || atomic_read(&tsk->mm->mm_users) > 1 ||

	    tsk->mm != tsk->active_mm || tsk->mm->ioctx_list)

		goto unlock;



	tsk->mm->context.pgstes = 1;	/* dirty little tricks .. */

	mm = dup_mm(tsk);

	tsk->mm->context.pgstes = 0;



	rc = -ENOMEM;

	if (!mm)

		goto unlock;

	mmput(tsk->mm);

	tsk->mm = tsk->active_mm = mm;

	preempt_disable();

	update_mm(mm, tsk);

	cpu_set(smp_processor_id(), mm->cpu_vm_mask);

	preempt_enable();

	rc = 0;

unlock:

	task_unlock(tsk);

	return rc;

}

EXPORT_SYMBOL_GPL(s390_enable_sie);

include/asm-s390/mmu.h

+1 −0
Original line number Diff line number Diff line
@@ -7,6 +7,7 @@ typedef struct { 
	unsigned long asce_bits;

	unsigned long asce_limit;

	int noexec;

	int pgstes;

} mm_context_t;



#endif

include/asm-s390/mmu_context.h

+7 −1
Original line number Diff line number Diff line
@@ -20,7 +20,13 @@ static inline int init_new_context(struct task_struct *tsk, 
#ifdef CONFIG_64BIT

	mm->context.asce_bits |= _ASCE_TYPE_REGION3;

#endif

	if (current->mm->context.pgstes) {

		mm->context.noexec = 0;

		mm->context.pgstes = 1;

	} else {

		mm->context.noexec = s390_noexec;

		mm->context.pgstes = 0;

	}

	mm->context.asce_limit = STACK_TOP_MAX;

	crst_table_init((unsigned long *) mm->pgd, pgd_entry_type(mm));

	return 0;