linux-kernel - [PATCH mm-unstable RFC 03/26] arc/mm: support __HAVE_ARCH_PTE_SWP

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Date:   Tue,  6 Dec 2022 15:47:07 +0100
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        John Hubbard <jhubbard@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Yang Shi <shy828301@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Nadav Amit <namit@...are.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Peter Xu <peterx@...hat.com>, linux-mm@...ck.org,
        x86@...nel.org, linux-alpha@...r.kernel.org,
        linux-snps-arc@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-csky@...r.kernel.org,
        linux-hexagon@...r.kernel.org, linux-ia64@...r.kernel.org,
        loongarch@...ts.linux.dev, linux-m68k@...ts.linux-m68k.org,
        linux-mips@...r.kernel.org, openrisc@...ts.librecores.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-um@...ts.infradead.org, linux-xtensa@...ux-xtensa.org,
        David Hildenbrand <david@...hat.com>,
        Vineet Gupta <vgupta@...nel.org>
Subject: [PATCH mm-unstable RFC 03/26] arc/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE

Let's support __HAVE_ARCH_PTE_SWP_EXCLUSIVE by using bit 5, which is yet
unused. The only important parts seems to be to not use _PAGE_PRESENT
(bit 9).

Cc: Vineet Gupta <vgupta@...nel.org>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 arch/arc/include/asm/pgtable-bits-arcv2.h | 27 ++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/arch/arc/include/asm/pgtable-bits-arcv2.h b/arch/arc/include/asm/pgtable-bits-arcv2.h
index 515e82db519f..611f412713b9 100644
--- a/arch/arc/include/asm/pgtable-bits-arcv2.h
+++ b/arch/arc/include/asm/pgtable-bits-arcv2.h
@@ -26,6 +26,9 @@
 #define _PAGE_GLOBAL		(1 << 8)  /* ASID agnostic (H) */
 #define _PAGE_PRESENT		(1 << 9)  /* PTE/TLB Valid (H) */
 
+/* We borrow bit 5 to store the exclusive marker in swap PTEs. */
+#define _PAGE_SWP_EXCLUSIVE	_PAGE_DIRTY
+
 #ifdef CONFIG_ARC_MMU_V4
 #define _PAGE_HW_SZ		(1 << 10)  /* Normal/super (H) */
 #else
@@ -106,9 +109,18 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
 void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
 		      pte_t *ptep);
 
-/* Encode swap {type,off} tuple into PTE
- * We reserve 13 bits for 5-bit @type, keeping bits 12-5 zero, ensuring that
- * PAGE_PRESENT is zero in a PTE holding swap "identifier"
+/*
+ * Encode/decode swap entries and swap PTEs. Swap PTEs are all PTEs that
+ * are !pte_none() && !pte_present().
+ *
+ * Format of swap PTEs:
+ *
+ *   3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1
+ *   1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+ *   <-------------- offset -------------> <--- zero --> E < type ->
+ *
+ *   E is the exclusive marker that is not stored in swap entries.
+ *   The zero'ed bits include _PAGE_PRESENT.
  */
 #define __swp_entry(type, off)		((swp_entry_t) \
 					{ ((type) & 0x1f) | ((off) << 13) })
@@ -120,6 +132,15 @@ void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
 #define __pte_to_swp_entry(pte)		((swp_entry_t) { pte_val(pte) })
 #define __swp_entry_to_pte(x)		((pte_t) { (x).val })
 
+#define __HAVE_ARCH_PTE_SWP_EXCLUSIVE
+static inline int pte_swp_exclusive(pte_t pte)
+{
+	return pte_val(pte) & _PAGE_SWP_EXCLUSIVE;
+}
+
+PTE_BIT_FUNC(swp_mkexclusive, |= (_PAGE_SWP_EXCLUSIVE));
+PTE_BIT_FUNC(swp_clear_exclusive, &= ~(_PAGE_SWP_EXCLUSIVE));
+
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 #include <asm/hugepage.h>
 #endif
-- 
2.38.1