arch/s390/include/asm/pgtable.h | 22 ++++++++++++++++++++++ arch/s390/mm/gmap_helpers.c | 12 +++++++++++- arch/s390/mm/pgtable.c | 23 +---------------------- 3 files changed, 34 insertions(+), 23 deletions(-)
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.
Suggested-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: Gautam Gala <ggala@linux.ibm.com>
---
arch/s390/include/asm/pgtable.h | 22 ++++++++++++++++++++++
arch/s390/mm/gmap_helpers.c | 12 +++++++++++-
arch/s390/mm/pgtable.c | 23 +----------------------
3 files changed, 34 insertions(+), 23 deletions(-)
diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index c1a7a92f0575..b7100c6a4054 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -2055,4 +2055,26 @@ 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 */
diff --git a/arch/s390/mm/gmap_helpers.c b/arch/s390/mm/gmap_helpers.c
index b63f427e7289..d4c3c36855e2 100644
--- a/arch/s390/mm/gmap_helpers.c
+++ b/arch/s390/mm/gmap_helpers.c
@@ -15,6 +15,7 @@
#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.
@@ -47,6 +48,7 @@ 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);
@@ -60,8 +62,16 @@ 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);
diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 60688be4e876..879f39366e6c 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -24,6 +24,7 @@
#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)
@@ -115,28 +116,6 @@ 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;
--
2.51.0Hi Gautam,
kernel test robot noticed the following build warnings:
[auto build test WARNING on s390/features]
[also build test WARNING on linus/master v6.17-rc7 next-20250926]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]
url: https://github.com/intel-lab-lkp/linux/commits/Gautam-Gala/KVM-s390-Fix-to-clear-PTE-when-discarding-a-swapped-page/20250924-201847
base: https://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git features
patch link: https://lore.kernel.org/r/20250924121707.145350-1-ggala%40linux.ibm.com
patch subject: [PATCH] KVM: s390: Fix to clear PTE when discarding a swapped page
config: s390-defconfig (https://download.01.org/0day-ci/archive/20250928/202509280003.NWFBhwme-lkp@intel.com/config)
compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project cafc064fc7a96b3979a023ddae1da2b499d6c954)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250928/202509280003.NWFBhwme-lkp@intel.com/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202509280003.NWFBhwme-lkp@intel.com/
All warnings (new ones prefixed by >>):
In file included from arch/s390/boot/als.c:9:
In file included from arch/s390/include/asm/sclp.h:26:
In file included from arch/s390/include/asm/chpid.h:10:
In file included from arch/s390/include/asm/cio.h:10:
In file included from arch/s390/include/asm/dma-types.h:7:
In file included from include/linux/io.h:12:
In file included from arch/s390/include/asm/io.h:15:
>> arch/s390/include/asm/pgtable.h:2065:48: warning: passing 'unsigned long *' to parameter of type 'long *' converts between pointers to integer types with different sign [-Wpointer-sign]
2065 | value = __atomic64_or_barrier(PGSTE_PCL_BIT, ptr);
| ^~~
arch/s390/include/asm/atomic_ops.h:161:1: note: passing argument to parameter 'ptr' here
161 | __ATOMIC64_OPS(__atomic64_or, "ogr")
| ^
arch/s390/include/asm/atomic_ops.h:157:2: note: expanded from macro '__ATOMIC64_OPS'
157 | __ATOMIC64_OP(op_name##_barrier, op_string)
| ^
arch/s390/include/asm/atomic_ops.h:141:53: note: expanded from macro '__ATOMIC64_OP'
141 | static __always_inline long op_name(long val, long *ptr) \
| ^
1 warning generated.
vim +2065 arch/s390/include/asm/pgtable.h
2057
2058 static inline pgste_t pgste_get_lock(pte_t *ptep)
2059 {
2060 unsigned long value = 0;
2061 #ifdef CONFIG_PGSTE
2062 unsigned long *ptr = (unsigned long *)(ptep + PTRS_PER_PTE);
2063
2064 do {
> 2065 value = __atomic64_or_barrier(PGSTE_PCL_BIT, ptr);
2066 } while (value & PGSTE_PCL_BIT);
2067 value |= PGSTE_PCL_BIT;
2068 #endif
2069 return __pgste(value);
2070 }
2071
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
On 24.09.25 14:17, Gautam Gala wrote: > 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. > > Suggested-by: Claudio Imbrenda <imbrenda@linux.ibm.com> > Signed-off-by: Gautam Gala <ggala@linux.ibm.com> > --- Sounds bad, I assume we want Fixes: and CC: stable, right? -- Cheers David / dhildenb
On Wed, 24 Sep 2025 14:22:05 +0200 David Hildenbrand <david@redhat.com> wrote: > On 24.09.25 14:17, Gautam Gala wrote: > > 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. > > > > Suggested-by: Claudio Imbrenda <imbrenda@linux.ibm.com> > > Signed-off-by: Gautam Gala <ggala@linux.ibm.com> > > --- > > Sounds bad, > > I assume we want Fixes: and CC: stable, right? yes; I'll add those when picking up Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
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