linux-kernel - [PATCH v6 06/38] mm: Add default definition of set

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Message-Id: <20230802151406.3735276-7-willy@infradead.org>
Date:   Wed,  2 Aug 2023 16:13:34 +0100
From:   "Matthew Wilcox (Oracle)" <willy@...radead.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Mike Rapoport <rppt@...nel.org>
Subject: [PATCH v6 06/38] mm: Add default definition of set_ptes()

Most architectures can just define set_pte() and PFN_PTE_SHIFT to
use this definition.  It's also a handy spot to document the guarantees
provided by the MM.

Suggested-by: Mike Rapoport (IBM) <rppt@...nel.org>
Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Reviewed-by: Mike Rapoport (IBM) <rppt@...nel.org>
---
 include/linux/pgtable.h | 81 ++++++++++++++++++++++++++++++-----------
 1 file changed, 60 insertions(+), 21 deletions(-)

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index f34e0f2cb4d8..3fde0d5d1c29 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -182,6 +182,66 @@ static inline int pmd_young(pmd_t pmd)
 }
 #endif
 
+/*
+ * A facility to provide lazy MMU batching.  This allows PTE updates and
+ * page invalidations to be delayed until a call to leave lazy MMU mode
+ * is issued.  Some architectures may benefit from doing this, and it is
+ * beneficial for both shadow and direct mode hypervisors, which may batch
+ * the PTE updates which happen during this window.  Note that using this
+ * interface requires that read hazards be removed from the code.  A read
+ * hazard could result in the direct mode hypervisor case, since the actual
+ * write to the page tables may not yet have taken place, so reads though
+ * a raw PTE pointer after it has been modified are not guaranteed to be
+ * up to date.  This mode can only be entered and left under the protection of
+ * the page table locks for all page tables which may be modified.  In the UP
+ * case, this is required so that preemption is disabled, and in the SMP case,
+ * it must synchronize the delayed page table writes properly on other CPUs.
+ */
+#ifndef __HAVE_ARCH_ENTER_LAZY_MMU_MODE
+#define arch_enter_lazy_mmu_mode()	do {} while (0)
+#define arch_leave_lazy_mmu_mode()	do {} while (0)
+#define arch_flush_lazy_mmu_mode()	do {} while (0)
+#endif
+
+#ifndef set_ptes
+#ifdef PFN_PTE_SHIFT
+/**
+ * set_ptes - Map consecutive pages to a contiguous range of addresses.
+ * @mm: Address space to map the pages into.
+ * @addr: Address to map the first page at.
+ * @ptep: Page table pointer for the first entry.
+ * @pte: Page table entry for the first page.
+ * @nr: Number of pages to map.
+ *
+ * May be overridden by the architecture, or the architecture can define
+ * set_pte() and PFN_PTE_SHIFT.
+ *
+ * Context: The caller holds the page table lock.  The pages all belong
+ * to the same folio.  The PTEs are all in the same PMD.
+ */
+static inline void set_ptes(struct mm_struct *mm, unsigned long addr,
+		pte_t *ptep, pte_t pte, unsigned int nr)
+{
+	page_table_check_ptes_set(mm, ptep, pte, nr);
+
+	arch_enter_lazy_mmu_mode();
+	for (;;) {
+		set_pte(ptep, pte);
+		if (--nr == 0)
+			break;
+		ptep++;
+		pte = __pte(pte_val(pte) + (1UL << PFN_PTE_SHIFT));
+	}
+	arch_leave_lazy_mmu_mode();
+}
+#ifndef set_pte_at
+#define set_pte_at(mm, addr, ptep, pte) set_ptes(mm, addr, ptep, pte, 1)
+#endif
+#endif
+#else
+#define set_pte_at(mm, addr, ptep, pte) set_ptes(mm, addr, ptep, pte, 1)
+#endif
+
 #ifndef __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
 extern int ptep_set_access_flags(struct vm_area_struct *vma,
 				 unsigned long address, pte_t *ptep,
@@ -1051,27 +1111,6 @@ static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
 #define pgprot_decrypted(prot)	(prot)
 #endif
 
-/*
- * A facility to provide lazy MMU batching.  This allows PTE updates and
- * page invalidations to be delayed until a call to leave lazy MMU mode
- * is issued.  Some architectures may benefit from doing this, and it is
- * beneficial for both shadow and direct mode hypervisors, which may batch
- * the PTE updates which happen during this window.  Note that using this
- * interface requires that read hazards be removed from the code.  A read
- * hazard could result in the direct mode hypervisor case, since the actual
- * write to the page tables may not yet have taken place, so reads though
- * a raw PTE pointer after it has been modified are not guaranteed to be
- * up to date.  This mode can only be entered and left under the protection of
- * the page table locks for all page tables which may be modified.  In the UP
- * case, this is required so that preemption is disabled, and in the SMP case,
- * it must synchronize the delayed page table writes properly on other CPUs.
- */
-#ifndef __HAVE_ARCH_ENTER_LAZY_MMU_MODE
-#define arch_enter_lazy_mmu_mode()	do {} while (0)
-#define arch_leave_lazy_mmu_mode()	do {} while (0)
-#define arch_flush_lazy_mmu_mode()	do {} while (0)
-#endif
-
 /*
  * A facility to provide batching of the reload of page tables and
  * other process state with the actual context switch code for
-- 
2.40.1