Commit 5deafa27 authored by Gautam Gala's avatar Gautam Gala Committed by Claudio Imbrenda
Browse files

KVM: s390: Fix to clear PTE when discarding a swapped page 



KVM run fails when guests with 'cmm' cpu feature and host are
under memory pressure and use swap heavily. This is because
npages becomes ENOMEN (out of memory) in hva_to_pfn_slow()
which inturn propagates as EFAULT to qemu. Clearing the page
table entry when discarding an address that maps to a swap
entry resolves the issue.

Fixes: 20019790 ("KVM: s390: Refactor and split some gmap helpers")
Cc: stable@vger.kernel.org
Suggested-by: default avatarClaudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: default avatarGautam Gala <ggala@linux.ibm.com>
Reviewed-by: default avatarClaudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: default avatarClaudio Imbrenda <imbrenda@linux.ibm.com>
parent 352ccf89

arch/s390/include/asm/pgtable.h

+22 −0
Original line number Diff line number Diff line
@@ -2010,4 +2010,26 @@ static inline unsigned long gmap_pgste_get_pgt_addr(unsigned long *pgt) 
	return res;

}



static inline pgste_t pgste_get_lock(pte_t *ptep)

{

	unsigned long value = 0;

#ifdef CONFIG_PGSTE

	unsigned long *ptr = (unsigned long *)(ptep + PTRS_PER_PTE);



	do {

		value = __atomic64_or_barrier(PGSTE_PCL_BIT, ptr);

	} while (value & PGSTE_PCL_BIT);

	value |= PGSTE_PCL_BIT;

#endif

	return __pgste(value);

}



static inline void pgste_set_unlock(pte_t *ptep, pgste_t pgste)

{

#ifdef CONFIG_PGSTE

	barrier();

	WRITE_ONCE(*(unsigned long *)(ptep + PTRS_PER_PTE), pgste_val(pgste) & ~PGSTE_PCL_BIT);

#endif

}



#endif /* _S390_PAGE_H */

arch/s390/mm/gmap_helpers.c

+11 −1
Original line number Diff line number Diff line
@@ -13,6 +13,7 @@ 
#include <linux/pagewalk.h>

#include <linux/ksm.h>

#include <asm/gmap_helpers.h>

#include <asm/pgtable.h>



/**

 * ptep_zap_swap_entry() - discard a swap entry.
@@ -45,6 +46,7 @@ void gmap_helper_zap_one_page(struct mm_struct *mm, unsigned long vmaddr) 
{

	struct vm_area_struct *vma;

	spinlock_t *ptl;

	pgste_t pgste;

	pte_t *ptep;



	mmap_assert_locked(mm);
@@ -58,8 +60,16 @@ void gmap_helper_zap_one_page(struct mm_struct *mm, unsigned long vmaddr) 
	ptep = get_locked_pte(mm, vmaddr, &ptl);

	if (unlikely(!ptep))

		return;

	if (pte_swap(*ptep))

	if (pte_swap(*ptep)) {

		preempt_disable();

		pgste = pgste_get_lock(ptep);



		ptep_zap_swap_entry(mm, pte_to_swp_entry(*ptep));

		pte_clear(mm, vmaddr, ptep);



		pgste_set_unlock(ptep, pgste);

		preempt_enable();

	}

	pte_unmap_unlock(ptep, ptl);

}

EXPORT_SYMBOL_GPL(gmap_helper_zap_one_page);

arch/s390/mm/pgtable.c

+1 −22
Original line number Diff line number Diff line
@@ -23,6 +23,7 @@ 
#include <asm/tlbflush.h>

#include <asm/mmu_context.h>

#include <asm/page-states.h>

#include <asm/pgtable.h>

#include <asm/machine.h>



pgprot_t pgprot_writecombine(pgprot_t prot)
@@ -114,28 +115,6 @@ static inline pte_t ptep_flush_lazy(struct mm_struct *mm, 
	return old;

}



static inline pgste_t pgste_get_lock(pte_t *ptep)

{

	unsigned long value = 0;

#ifdef CONFIG_PGSTE

	unsigned long *ptr = (unsigned long *)(ptep + PTRS_PER_PTE);



	do {

		value = __atomic64_or_barrier(PGSTE_PCL_BIT, ptr);

	} while (value & PGSTE_PCL_BIT);

	value |= PGSTE_PCL_BIT;

#endif

	return __pgste(value);

}



static inline void pgste_set_unlock(pte_t *ptep, pgste_t pgste)

{

#ifdef CONFIG_PGSTE

	barrier();

	WRITE_ONCE(*(unsigned long *)(ptep + PTRS_PER_PTE), pgste_val(pgste) & ~PGSTE_PCL_BIT);

#endif

}



static inline pgste_t pgste_get(pte_t *ptep)

{

	unsigned long pgste = 0;