[PATCH 1/5] powerpc/mm: define empty update_mmu_cache() as static inline

[PATCH 1/5] powerpc/mm: define empty update_mmu_cache() as static inline

[Christophe Leroy]

Only BOOK3S and FSL_BOOK3E have a usefull update_mmu_cache().

For the others, just define it static inline.

In the meantime, simplify the FSL_BOOK3E related ifdef as
book3e_hugetlb_preload() only exists when CONFIG_PPC_FSL_BOOK3E
is selected.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 arch/powerpc/include/asm/book3s/pgtable.h | 11 +++++++++++
 arch/powerpc/include/asm/nohash/pgtable.h | 13 +++++++++++++
 arch/powerpc/include/asm/pgtable.h        | 12 ------------
 arch/powerpc/mm/mem.c                     | 11 +++++++----
 4 files changed, 31 insertions(+), 16 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/pgtable.h b/arch/powerpc/include/asm/book3s/pgtable.h
index 6436b65ac7bc..0e1263455d73 100644
--- a/arch/powerpc/include/asm/book3s/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/pgtable.h
@@ -26,5 +26,16 @@ extern pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
 				     unsigned long size, pgprot_t vma_prot);
 #define __HAVE_PHYS_MEM_ACCESS_PROT
 
+/*
+ * This gets called at the end of handling a page fault, when
+ * the kernel has put a new PTE into the page table for the process.
+ * We use it to ensure coherency between the i-cache and d-cache
+ * for the page which has just been mapped in.
+ * On machines which use an MMU hash table, we use this to put a
+ * corresponding HPTE into the hash table ahead of time, instead of
+ * waiting for the inevitable extra hash-table miss exception.
+ */
+void update_mmu_cache(struct vm_area_struct *vma, unsigned long address, pte_t *ptep);
+
 #endif /* __ASSEMBLY__ */
 #endif
diff --git a/arch/powerpc/include/asm/nohash/pgtable.h b/arch/powerpc/include/asm/nohash/pgtable.h
index 1ca1c1864b32..7fed9dc0f147 100644
--- a/arch/powerpc/include/asm/nohash/pgtable.h
+++ b/arch/powerpc/include/asm/nohash/pgtable.h
@@ -293,5 +293,18 @@ static inline int pgd_huge(pgd_t pgd)
 #define is_hugepd(hpd)		(hugepd_ok(hpd))
 #endif
 
+/*
+ * This gets called at the end of handling a page fault, when
+ * the kernel has put a new PTE into the page table for the process.
+ * We use it to ensure coherency between the i-cache and d-cache
+ * for the page which has just been mapped in.
+ */
+#if defined(CONFIG_PPC_FSL_BOOK3E) && defined(CONFIG_HUGETLB_PAGE)
+void update_mmu_cache(struct vm_area_struct *vma, unsigned long address, pte_t *ptep);
+#else
+static inline
+void update_mmu_cache(struct vm_area_struct *vma, unsigned long address, pte_t *ptep) {}
+#endif
+
 #endif /* __ASSEMBLY__ */
 #endif
diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
index c58ba7963688..c70916a7865a 100644
--- a/arch/powerpc/include/asm/pgtable.h
+++ b/arch/powerpc/include/asm/pgtable.h
@@ -77,18 +77,6 @@ extern void paging_init(void);
 
 #include <asm-generic/pgtable.h>
 
-
-/*
- * This gets called at the end of handling a page fault, when
- * the kernel has put a new PTE into the page table for the process.
- * We use it to ensure coherency between the i-cache and d-cache
- * for the page which has just been mapped in.
- * On machines which use an MMU hash table, we use this to put a
- * corresponding HPTE into the hash table ahead of time, instead of
- * waiting for the inevitable extra hash-table miss exception.
- */
-extern void update_mmu_cache(struct vm_area_struct *, unsigned long, pte_t *);
-
 #ifndef CONFIG_TRANSPARENT_HUGEPAGE
 #define pmd_large(pmd)		0
 #endif
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 9191a66b3bc5..582ad728ac9d 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -414,10 +414,10 @@ EXPORT_SYMBOL(flush_icache_user_range);
  * 
  * This must always be called with the pte lock held.
  */
+#ifdef CONFIG_PPC_BOOK3S
 void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
 		      pte_t *ptep)
 {
-#ifdef CONFIG_PPC_BOOK3S
 	/*
 	 * We don't need to worry about _PAGE_PRESENT here because we are
 	 * called with either mm->page_table_lock held or ptl lock held
@@ -455,13 +455,16 @@ void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
 	}
 
 	hash_preload(vma->vm_mm, address, is_exec, trap);
+}
 #endif /* CONFIG_PPC_BOOK3S */
-#if (defined(CONFIG_PPC_BOOK3E_64) || defined(CONFIG_PPC_FSL_BOOK3E)) \
-	&& defined(CONFIG_HUGETLB_PAGE)
+#if defined(CONFIG_PPC_FSL_BOOK3E) && defined(CONFIG_HUGETLB_PAGE)
+void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
+		      pte_t *ptep)
+{
 	if (is_vm_hugetlb_page(vma))
 		book3e_hugetlb_preload(vma, address, *ptep);
-#endif
 }
+#endif
 
 /*
  * System memory should not be in /proc/iomem but various tools expect it
-- 
2.13.3

[PATCH 2/5] powerpc/mm: move FSL_BOOK3 version of update_mmu_cache()

[Christophe Leroy]

Move FSL_BOOK3E version of update_mmu_cache() at the same
place as book3e_hugetlb_preload() as update_mmu_cache() is
the only user of book3e_hugetlb_preload().

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 arch/powerpc/include/asm/hugetlb.h          |  3 ---
 arch/powerpc/mm/mem.c                       |  8 --------
 arch/powerpc/mm/nohash/book3e_hugetlbpage.c | 16 ++++++++++++++--
 3 files changed, 14 insertions(+), 13 deletions(-)

diff --git a/arch/powerpc/include/asm/hugetlb.h b/arch/powerpc/include/asm/hugetlb.h
index 20a101046cff..bd6504c28c2f 100644
--- a/arch/powerpc/include/asm/hugetlb.h
+++ b/arch/powerpc/include/asm/hugetlb.h
@@ -31,9 +31,6 @@ static inline int is_hugepage_only_range(struct mm_struct *mm,
 	return 0;
 }
 
-void book3e_hugetlb_preload(struct vm_area_struct *vma, unsigned long ea,
-			    pte_t pte);
-
 #define __HAVE_ARCH_HUGETLB_FREE_PGD_RANGE
 void hugetlb_free_pgd_range(struct mmu_gather *tlb, unsigned long addr,
 			    unsigned long end, unsigned long floor,
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 582ad728ac9d..c45d44538ddb 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -457,14 +457,6 @@ void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
 	hash_preload(vma->vm_mm, address, is_exec, trap);
 }
 #endif /* CONFIG_PPC_BOOK3S */
-#if defined(CONFIG_PPC_FSL_BOOK3E) && defined(CONFIG_HUGETLB_PAGE)
-void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
-		      pte_t *ptep)
-{
-	if (is_vm_hugetlb_page(vma))
-		book3e_hugetlb_preload(vma, address, *ptep);
-}
-#endif
 
 /*
  * System memory should not be in /proc/iomem but various tools expect it
diff --git a/arch/powerpc/mm/nohash/book3e_hugetlbpage.c b/arch/powerpc/mm/nohash/book3e_hugetlbpage.c
index 61915f4d3c7f..8b88be91b622 100644
--- a/arch/powerpc/mm/nohash/book3e_hugetlbpage.c
+++ b/arch/powerpc/mm/nohash/book3e_hugetlbpage.c
@@ -122,8 +122,8 @@ static inline int book3e_tlb_exists(unsigned long ea, unsigned long pid)
 	return found;
 }
 
-void book3e_hugetlb_preload(struct vm_area_struct *vma, unsigned long ea,
-			    pte_t pte)
+static void
+book3e_hugetlb_preload(struct vm_area_struct *vma, unsigned long ea, pte_t pte)
 {
 	unsigned long mas1, mas2;
 	u64 mas7_3;
@@ -183,6 +183,18 @@ void book3e_hugetlb_preload(struct vm_area_struct *vma, unsigned long ea,
 	local_irq_restore(flags);
 }
 
+/*
+ * This is called at the end of handling a user page fault, when the
+ * fault has been handled by updating a PTE in the linux page tables.
+ *
+ * This must always be called with the pte lock held.
+ */
+void update_mmu_cache(struct vm_area_struct *vma, unsigned long address, pte_t *ptep)
+{
+	if (is_vm_hugetlb_page(vma))
+		book3e_hugetlb_preload(vma, address, *ptep);
+}
+
 void flush_hugetlb_page(struct vm_area_struct *vma, unsigned long vmaddr)
 {
 	struct hstate *hstate = hstate_file(vma->vm_file);
-- 
2.13.3

[PATCH 3/5] powerpc/mm: move update_mmu_cache() into book3s hash utils.

[Christophe Leroy]

update_mmu_cache() is only for BOOK3S, and can be simplified
for BOOK3S32.

Move it out of mem.c into respective BOOK3S32 and BOOK3S64
files containing hash utils.

BOOK3S64 version of hash_preload() is only used locally,
declare it static.

Remove the radix_enabled() stuff in BOOK3S32 version.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 arch/powerpc/mm/book3s32/mmu.c        | 45 +++++++++++++++++++++++++++++
 arch/powerpc/mm/book3s64/hash_utils.c | 54 +++++++++++++++++++++++++++++++++--
 arch/powerpc/mm/mem.c                 | 52 ---------------------------------
 arch/powerpc/mm/mmu_decl.h            |  7 ++---
 4 files changed, 100 insertions(+), 58 deletions(-)

diff --git a/arch/powerpc/mm/book3s32/mmu.c b/arch/powerpc/mm/book3s32/mmu.c
index e249fbf6b9c3..3e3c4077cdb7 100644
--- a/arch/powerpc/mm/book3s32/mmu.c
+++ b/arch/powerpc/mm/book3s32/mmu.c
@@ -310,6 +310,51 @@ void hash_preload(struct mm_struct *mm, unsigned long ea,
 }
 
 /*
+ * This is called at the end of handling a user page fault, when the
+ * fault has been handled by updating a PTE in the linux page tables.
+ * We use it to preload an HPTE into the hash table corresponding to
+ * the updated linux PTE.
+ *
+ * This must always be called with the pte lock held.
+ */
+void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
+		      pte_t *ptep)
+{
+	/*
+	 * We don't need to worry about _PAGE_PRESENT here because we are
+	 * called with either mm->page_table_lock held or ptl lock held
+	 */
+	unsigned long trap;
+	bool is_exec;
+
+	/* We only want HPTEs for linux PTEs that have _PAGE_ACCESSED set */
+	if (!pte_young(*ptep) || address >= TASK_SIZE)
+		return;
+
+	/* We try to figure out if we are coming from an instruction
+	 * access fault and pass that down to __hash_page so we avoid
+	 * double-faulting on execution of fresh text. We have to test
+	 * for regs NULL since init will get here first thing at boot
+	 *
+	 * We also avoid filling the hash if not coming from a fault
+	 */
+
+	trap = current->thread.regs ? TRAP(current->thread.regs) : 0UL;
+	switch (trap) {
+	case 0x300:
+		is_exec = false;
+		break;
+	case 0x400:
+		is_exec = true;
+		break;
+	default:
+		return;
+	}
+
+	hash_preload(vma->vm_mm, address, is_exec, trap);
+}
+
+/*
  * Initialize the hash table and patch the instructions in hashtable.S.
  */
 void __init MMU_init_hw(void)
diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
index e6d471058597..fdad5bc07d79 100644
--- a/arch/powerpc/mm/book3s64/hash_utils.c
+++ b/arch/powerpc/mm/book3s64/hash_utils.c
@@ -1518,8 +1518,8 @@ static bool should_hash_preload(struct mm_struct *mm, unsigned long ea)
 }
 #endif
 
-void hash_preload(struct mm_struct *mm, unsigned long ea,
-		  bool is_exec, unsigned long trap)
+static void hash_preload(struct mm_struct *mm, unsigned long ea,
+			 bool is_exec, unsigned long trap)
 {
 	int hugepage_shift;
 	unsigned long vsid;
@@ -1599,6 +1599,56 @@ void hash_preload(struct mm_struct *mm, unsigned long ea,
 	local_irq_restore(flags);
 }
 
+/*
+ * This is called at the end of handling a user page fault, when the
+ * fault has been handled by updating a PTE in the linux page tables.
+ * We use it to preload an HPTE into the hash table corresponding to
+ * the updated linux PTE.
+ *
+ * This must always be called with the pte lock held.
+ */
+void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
+		      pte_t *ptep)
+{
+	/*
+	 * We don't need to worry about _PAGE_PRESENT here because we are
+	 * called with either mm->page_table_lock held or ptl lock held
+	 */
+	unsigned long trap;
+	bool is_exec;
+
+	if (radix_enabled()) {
+		prefetch((void *)address);
+		return;
+	}
+
+	/* We only want HPTEs for linux PTEs that have _PAGE_ACCESSED set */
+	if (!pte_young(*ptep) || address >= TASK_SIZE)
+		return;
+
+	/* We try to figure out if we are coming from an instruction
+	 * access fault and pass that down to __hash_page so we avoid
+	 * double-faulting on execution of fresh text. We have to test
+	 * for regs NULL since init will get here first thing at boot
+	 *
+	 * We also avoid filling the hash if not coming from a fault
+	 */
+
+	trap = current->thread.regs ? TRAP(current->thread.regs) : 0UL;
+	switch (trap) {
+	case 0x300:
+		is_exec = false;
+		break;
+	case 0x400:
+		is_exec = true;
+		break;
+	default:
+		return;
+	}
+
+	hash_preload(vma->vm_mm, address, is_exec, trap);
+}
+
 #ifdef CONFIG_PPC_MEM_KEYS
 /*
  * Return the protection key associated with the given address and the
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index c45d44538ddb..3e9e9a051c93 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -407,58 +407,6 @@ void flush_icache_user_range(struct vm_area_struct *vma, struct page *page,
 EXPORT_SYMBOL(flush_icache_user_range);
 
 /*
- * This is called at the end of handling a user page fault, when the
- * fault has been handled by updating a PTE in the linux page tables.
- * We use it to preload an HPTE into the hash table corresponding to
- * the updated linux PTE.
- * 
- * This must always be called with the pte lock held.
- */
-#ifdef CONFIG_PPC_BOOK3S
-void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
-		      pte_t *ptep)
-{
-	/*
-	 * We don't need to worry about _PAGE_PRESENT here because we are
-	 * called with either mm->page_table_lock held or ptl lock held
-	 */
-	unsigned long trap;
-	bool is_exec;
-
-	if (radix_enabled()) {
-		prefetch((void *)address);
-		return;
-	}
-
-	/* We only want HPTEs for linux PTEs that have _PAGE_ACCESSED set */
-	if (!pte_young(*ptep) || address >= TASK_SIZE)
-		return;
-
-	/* We try to figure out if we are coming from an instruction
-	 * access fault and pass that down to __hash_page so we avoid
-	 * double-faulting on execution of fresh text. We have to test
-	 * for regs NULL since init will get here first thing at boot
-	 *
-	 * We also avoid filling the hash if not coming from a fault
-	 */
-
-	trap = current->thread.regs ? TRAP(current->thread.regs) : 0UL;
-	switch (trap) {
-	case 0x300:
-		is_exec = false;
-		break;
-	case 0x400:
-		is_exec = true;
-		break;
-	default:
-		return;
-	}
-
-	hash_preload(vma->vm_mm, address, is_exec, trap);
-}
-#endif /* CONFIG_PPC_BOOK3S */
-
-/*
  * System memory should not be in /proc/iomem but various tools expect it
  * (eg kdump).
  */
diff --git a/arch/powerpc/mm/mmu_decl.h b/arch/powerpc/mm/mmu_decl.h
index 32c1a191c28a..9f325a7a09cb 100644
--- a/arch/powerpc/mm/mmu_decl.h
+++ b/arch/powerpc/mm/mmu_decl.h
@@ -82,10 +82,6 @@ static inline void print_system_hash_info(void) {}
 
 #else /* CONFIG_PPC_MMU_NOHASH */
 
-extern void hash_preload(struct mm_struct *mm, unsigned long ea,
-			 bool is_exec, unsigned long trap);
-
-
 extern void _tlbie(unsigned long address);
 extern void _tlbia(void);
 
@@ -95,6 +91,9 @@ void print_system_hash_info(void);
 
 #ifdef CONFIG_PPC32
 
+void hash_preload(struct mm_struct *mm, unsigned long ea,
+		  bool is_exec, unsigned long trap);
+
 extern void mapin_ram(void);
 extern void setbat(int index, unsigned long virt, phys_addr_t phys,
 		   unsigned int size, pgprot_t prot);
-- 
2.13.3

[PATCH 4/5] powerpc/mm: Simplify update_mmu_cache() on BOOK3S32

[Christophe Leroy]

On BOOK3S32, hash_preload() neither use is_exec nor trap,
so drop those parameters and simplify update_mmu_cached().

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 arch/powerpc/mm/book3s32/mmu.c | 29 +++++++----------------------
 arch/powerpc/mm/mmu_decl.h     |  3 +--
 arch/powerpc/mm/pgtable_32.c   |  2 +-
 3 files changed, 9 insertions(+), 25 deletions(-)

diff --git a/arch/powerpc/mm/book3s32/mmu.c b/arch/powerpc/mm/book3s32/mmu.c
index 3e3c4077cdb7..3a62bf99f93f 100644
--- a/arch/powerpc/mm/book3s32/mmu.c
+++ b/arch/powerpc/mm/book3s32/mmu.c
@@ -297,8 +297,7 @@ void __init setbat(int index, unsigned long virt, phys_addr_t phys,
 /*
  * Preload a translation in the hash table
  */
-void hash_preload(struct mm_struct *mm, unsigned long ea,
-		  bool is_exec, unsigned long trap)
+void hash_preload(struct mm_struct *mm, unsigned long ea)
 {
 	pmd_t *pmd;
 
@@ -324,34 +323,20 @@ void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
 	 * We don't need to worry about _PAGE_PRESENT here because we are
 	 * called with either mm->page_table_lock held or ptl lock held
 	 */
-	unsigned long trap;
-	bool is_exec;
 
 	/* We only want HPTEs for linux PTEs that have _PAGE_ACCESSED set */
 	if (!pte_young(*ptep) || address >= TASK_SIZE)
 		return;
 
-	/* We try to figure out if we are coming from an instruction
-	 * access fault and pass that down to __hash_page so we avoid
-	 * double-faulting on execution of fresh text. We have to test
-	 * for regs NULL since init will get here first thing at boot
-	 *
-	 * We also avoid filling the hash if not coming from a fault
-	 */
+	/* We have to test for regs NULL since init will get here first thing at boot */
+	if (!current->thread.regs)
+		return;
 
-	trap = current->thread.regs ? TRAP(current->thread.regs) : 0UL;
-	switch (trap) {
-	case 0x300:
-		is_exec = false;
-		break;
-	case 0x400:
-		is_exec = true;
-		break;
-	default:
+	/* We also avoid filling the hash if not coming from a fault */
+	if (TRAP(current->thread.regs) != 0x300 && TRAP(current->thread.regs) != 0x400)
 		return;
-	}
 
-	hash_preload(vma->vm_mm, address, is_exec, trap);
+	hash_preload(vma->vm_mm, address);
 }
 
 /*
diff --git a/arch/powerpc/mm/mmu_decl.h b/arch/powerpc/mm/mmu_decl.h
index 9f325a7a09cb..adbaf2167214 100644
--- a/arch/powerpc/mm/mmu_decl.h
+++ b/arch/powerpc/mm/mmu_decl.h
@@ -91,8 +91,7 @@ void print_system_hash_info(void);
 
 #ifdef CONFIG_PPC32
 
-void hash_preload(struct mm_struct *mm, unsigned long ea,
-		  bool is_exec, unsigned long trap);
+void hash_preload(struct mm_struct *mm, unsigned long ea);
 
 extern void mapin_ram(void);
 extern void setbat(int index, unsigned long virt, phys_addr_t phys,
diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
index 35cb96cfc258..97f401a06fcc 100644
--- a/arch/powerpc/mm/pgtable_32.c
+++ b/arch/powerpc/mm/pgtable_32.c
@@ -252,7 +252,7 @@ static void __init __mapin_ram_chunk(unsigned long offset, unsigned long top)
 		map_kernel_page(v, p, ktext ? PAGE_KERNEL_TEXT : PAGE_KERNEL);
 #ifdef CONFIG_PPC_BOOK3S_32
 		if (ktext)
-			hash_preload(&init_mm, v, false, 0x300);
+			hash_preload(&init_mm, v);
 #endif
 		v += PAGE_SIZE;
 		p += PAGE_SIZE;
-- 
2.13.3

[PATCH 5/5] powerpc/mm: ppc 603 doesn't need update_mmu_cache()

[Christophe Leroy]

On powerpc 603, there is no hash table so get out of
update_mmu_cache() early.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 arch/powerpc/mm/book3s32/mmu.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/powerpc/mm/book3s32/mmu.c b/arch/powerpc/mm/book3s32/mmu.c
index 3a62bf99f93f..c20269be79ec 100644
--- a/arch/powerpc/mm/book3s32/mmu.c
+++ b/arch/powerpc/mm/book3s32/mmu.c
@@ -319,6 +319,8 @@ void hash_preload(struct mm_struct *mm, unsigned long ea)
 void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
 		      pte_t *ptep)
 {
+	if (!mmu_has_feature(MMU_FTR_HPTE_TABLE))
+		return;
 	/*
 	 * We don't need to worry about _PAGE_PRESENT here because we are
 	 * called with either mm->page_table_lock held or ptl lock held
-- 
2.13.3

Re: [PATCH 1/5] powerpc/mm: define empty update_mmu_cache() as static inline

[Michael Ellerman]

On Fri, 2019-08-16 at 05:41:40 UTC, Christophe Leroy wrote:
> Only BOOK3S and FSL_BOOK3E have a usefull update_mmu_cache().
> 
> For the others, just define it static inline.
> 
> In the meantime, simplify the FSL_BOOK3E related ifdef as
> book3e_hugetlb_preload() only exists when CONFIG_PPC_FSL_BOOK3E
> is selected.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>

Series applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/d9642117914c9d3f800b3bacc19d7e388b04edb4

cheers