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arm/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE 

Let's support __HAVE_ARCH_PTE_SWP_EXCLUSIVE by stealing one bit from the
offset.  This reduces the maximum swap space per file to 64 GiB (was 128
GiB).

While at it drop the PTE_TYPE_FAULT from __swp_entry_to_pte() which is
defined to be 0 and is rather confusing because we should be dealing with
"Linux PTEs" not "hardware PTEs".  Also, properly mask the type in
__swp_entry().

Link: https://lkml.kernel.org/r/20230113171026.582290-5-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2023-01-13 18:10:04 +01:00 committed by Andrew Morton
parent 4a446b3dd3
commit 20aae9eff5
3 changed files with 34 additions and 7 deletions
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3
arch/arm/include/asm/pgtable-2level.h
View File

@ -126,6 +126,9 @@
#define L_PTE_SHARED (_AT(pteval_t, 1) << 10) /* shared(v6), coherent(xsc3) */
#define L_PTE_NONE (_AT(pteval_t, 1) << 11)
/* We borrow bit 7 to store the exclusive marker in swap PTEs. */
#define L_PTE_SWP_EXCLUSIVE L_PTE_RDONLY
/*
* These are the memory types, defined to be compatible with
* pre-ARMv6 CPUs cacheable and bufferable bits: n/a,n/a,C,B

3
arch/arm/include/asm/pgtable-3level.h
View File

@ -76,6 +76,9 @@
#define L_PTE_NONE (_AT(pteval_t, 1) << 57) /* PROT_NONE */
#define L_PTE_RDONLY (_AT(pteval_t, 1) << 58) /* READ ONLY */
/* We borrow bit 7 to store the exclusive marker in swap PTEs. */
#define L_PTE_SWP_EXCLUSIVE (_AT(pteval_t, 1) << 7)
#define L_PMD_SECT_VALID (_AT(pmdval_t, 1) << 0)
#define L_PMD_SECT_DIRTY (_AT(pmdval_t, 1) << 55)
#define L_PMD_SECT_NONE (_AT(pmdval_t, 1) << 57)

35
arch/arm/include/asm/pgtable.h
View File

@ -271,27 +271,48 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
}
/*
* Encode and decode a swap entry. Swap entries are stored in the Linux
* page tables as follows:
* 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 ------------------------> < type -> 0 0
* <------------------- offset ------------------> E < type -> 0 0
*
* This gives us up to 31 swap files and 128GB per swap file. Note that
* E is the exclusive marker that is not stored in swap entries.
*
* This gives us up to 31 swap files and 64GB per swap file. Note that
* the offset field is always non-zero.
*/
#define __SWP_TYPE_SHIFT 2
#define __SWP_TYPE_BITS 5
#define __SWP_TYPE_MASK ((1 << __SWP_TYPE_BITS) - 1)
#define __SWP_OFFSET_SHIFT (__SWP_TYPE_BITS + __SWP_TYPE_SHIFT)
#define __SWP_OFFSET_SHIFT (__SWP_TYPE_BITS + __SWP_TYPE_SHIFT + 1)
#define __swp_type(x) (((x).val >> __SWP_TYPE_SHIFT) & __SWP_TYPE_MASK)
#define __swp_offset(x) ((x).val >> __SWP_OFFSET_SHIFT)
#define __swp_entry(type,offset) ((swp_entry_t) { ((type) << __SWP_TYPE_SHIFT) | ((offset) << __SWP_OFFSET_SHIFT) })
#define __swp_entry(type, offset) ((swp_entry_t) { (((type) & __SWP_TYPE_BITS) << __SWP_TYPE_SHIFT) | \
((offset) << __SWP_OFFSET_SHIFT) })
#define __pte_to_swp_entry(pte) ((swp_entry_t) { pte_val(pte) })
#define __swp_entry_to_pte(swp) __pte((swp).val | PTE_TYPE_FAULT)
#define __swp_entry_to_pte(swp) __pte((swp).val)
#define __HAVE_ARCH_PTE_SWP_EXCLUSIVE
static inline int pte_swp_exclusive(pte_t pte)
{
return pte_isset(pte, L_PTE_SWP_EXCLUSIVE);
}
static inline pte_t pte_swp_mkexclusive(pte_t pte)
{
return set_pte_bit(pte, __pgprot(L_PTE_SWP_EXCLUSIVE));
}
static inline pte_t pte_swp_clear_exclusive(pte_t pte)
{
return clear_pte_bit(pte, __pgprot(L_PTE_SWP_EXCLUSIVE));
}
/*
* It is an error for the kernel to have more swap files than we can