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mm, virt: merge AS_UNMOVABLE and AS_INACCESSIBLE

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The flags AS_UNMOVABLE and AS_INACCESSIBLE were both added just for guest_memfd;
AS_UNMOVABLE is already in existing versions of Linux, while AS_INACCESSIBLE was
acked for inclusion in 6.11.

But really, they are the same thing: only guest_memfd uses them, at least for
now, and guest_memfd pages are unmovable because they should not be
accessed by the CPU.

So merge them into one; use the AS_INACCESSIBLE name which is more comprehensive.
At the same time, this fixes an embarrassing bug where AS_INACCESSIBLE was used
as a bit mask, despite it being just a bit index.

The bug was mostly benign, because AS_INACCESSIBLE's bit representation (1010)
corresponded to setting AS_UNEVICTABLE (which is already set) and AS_ENOSPC
(except no async writes can happen on the guest_memfd).  So the AS_INACCESSIBLE
flag simply had no effect.

Fixes: 1d23040caa ("KVM: guest_memfd: Use AS_INACCESSIBLE when creating guest_memfd inode")
Fixes: c72ceafbd1 ("mm: Introduce AS_INACCESSIBLE for encrypted/confidential memory")
Cc: linux-mm@kvack.org
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Hildenbrand <david@redhat.com>
Tested-by: Michael Roth <michael.roth@amd.com>
Reviewed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2024-07-11 13:56:54 -04:00
parent 02b0d3b9d4
commit 27e6a24a4c
5 changed files with 16 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
include/linux/pagemap.h
View File

@ -208,8 +208,8 @@ enum mapping_flags {
AS_RELEASE_ALWAYS, /* Call ->release_folio(), even if no private data */
AS_STABLE_WRITES, /* must wait for writeback before modifying
folio contents */
AS_UNMOVABLE, /* The mapping cannot be moved, ever */
AS_INACCESSIBLE, /* Do not attempt direct R/W access to the mapping */
AS_INACCESSIBLE, /* Do not attempt direct R/W access to the mapping,
including to move the mapping */
};
/**
@ -310,20 +310,20 @@ static inline void mapping_clear_stable_writes(struct address_space *mapping)
clear_bit(AS_STABLE_WRITES, &mapping->flags);
}
static inline void mapping_set_unmovable(struct address_space *mapping)
static inline void mapping_set_inaccessible(struct address_space *mapping)
{
/*
* It's expected unmovable mappings are also unevictable. Compaction
* It's expected inaccessible mappings are also unevictable. Compaction
* migrate scanner (isolate_migratepages_block()) relies on this to
* reduce page locking.
*/
set_bit(AS_UNEVICTABLE, &mapping->flags);
set_bit(AS_UNMOVABLE, &mapping->flags);
set_bit(AS_INACCESSIBLE, &mapping->flags);
}
static inline bool mapping_unmovable(struct address_space *mapping)
static inline bool mapping_inaccessible(struct address_space *mapping)
{
return test_bit(AS_UNMOVABLE, &mapping->flags);
return test_bit(AS_INACCESSIBLE, &mapping->flags);
}
static inline gfp_t mapping_gfp_mask(struct address_space * mapping)

12
mm/compaction.c
View File

@ -1172,22 +1172,22 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
if (((mode & ISOLATE_ASYNC_MIGRATE) && is_dirty) ||
(mapping && is_unevictable)) {
bool migrate_dirty = true;
bool is_unmovable;
bool is_inaccessible;
/*
* Only folios without mappings or that have
* a ->migrate_folio callback are possible to migrate
* without blocking.
*
* Folios from unmovable mappings are not migratable.
* Folios from inaccessible mappings are not migratable.
*
* However, we can be racing with truncation, which can
* free the mapping that we need to check. Truncation
* holds the folio lock until after the folio is removed
* from the page so holding it ourselves is sufficient.
*
* To avoid locking the folio just to check unmovable,
* assume every unmovable folio is also unevictable,
* To avoid locking the folio just to check inaccessible,
* assume every inaccessible folio is also unevictable,
* which is a cheaper test. If our assumption goes
* wrong, it's not a correctness bug, just potentially
* wasted cycles.
@ -1200,9 +1200,9 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
migrate_dirty = !mapping ||
mapping->a_ops->migrate_folio;
}
is_unmovable = mapping && mapping_unmovable(mapping);
is_inaccessible = mapping && mapping_inaccessible(mapping);
folio_unlock(folio);
if (!migrate_dirty || is_unmovable)
if (!migrate_dirty || is_inaccessible)
goto isolate_fail_put;
}

2
mm/migrate.c
View File

@ -965,7 +965,7 @@ static int move_to_new_folio(struct folio *dst, struct folio *src,
if (!mapping)
rc = migrate_folio(mapping, dst, src, mode);
else if (mapping_unmovable(mapping))
else if (mapping_inaccessible(mapping))
rc = -EOPNOTSUPP;
else if (mapping->a_ops->migrate_folio)
/*

2
mm/truncate.c
View File

@ -233,7 +233,7 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end)
* doing a complex calculation here, and then doing the zeroing
* anyway if the page split fails.
*/
if (!(folio->mapping->flags & AS_INACCESSIBLE))
if (!mapping_inaccessible(folio->mapping))
folio_zero_range(folio, offset, length);
if (folio_has_private(folio))

3
virt/kvm/guest_memfd.c
View File

@ -416,11 +416,10 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
inode->i_private = (void *)(unsigned long)flags;
inode->i_op = &kvm_gmem_iops;
inode->i_mapping->a_ops = &kvm_gmem_aops;
inode->i_mapping->flags |= AS_INACCESSIBLE;
inode->i_mode |= S_IFREG;
inode->i_size = size;
mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
mapping_set_unmovable(inode->i_mapping);
mapping_set_inaccessible(inode->i_mapping);
/* Unmovable mappings are supposed to be marked unevictable as well. */
WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping));