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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-changelog] [xen master] mm.h: add helper function to test-and-clear _PGC_allocated
commit ec83f8256276c6f99dfe13bb2b56d168c080f098
Author: Paul Durrant <paul.durrant@xxxxxxxxxx>
AuthorDate: Tue Jul 16 09:10:36 2019 +0200
Commit: Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jul 16 09:10:36 2019 +0200
mm.h: add helper function to test-and-clear _PGC_allocated
The _PGC_allocated flag is set on a page when it is assigned to a domain
along with an initial reference count of at least 1. To clear this
'allocation' reference it is necessary to test-and-clear _PGC_allocated and
then only drop the reference if the test-and-clear succeeds. This is open-
coded in many places. It is also unsafe to test-and-clear _PGC_allocated
unless the caller holds an additional reference.
This patch adds a helper function, put_page_alloc_ref(), to replace all the
open-coded test-and-clear/put_page occurrences. That helper function
incorporates a check that an additional page reference is held and will
BUG() if it is not.
Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
xen/arch/arm/domain.c | 4 +---
xen/arch/x86/domain.c | 3 +--
xen/arch/x86/hvm/ioreq.c | 11 ++---------
xen/arch/x86/mm.c | 3 +--
xen/arch/x86/mm/mem_sharing.c | 9 +++------
xen/arch/x86/mm/p2m-pod.c | 4 +---
xen/arch/x86/mm/p2m.c | 3 +--
xen/common/grant_table.c | 3 +--
xen/common/memory.c | 5 ++---
xen/common/xenoprof.c | 3 +--
xen/include/xen/mm.h | 14 ++++++++++++++
11 files changed, 28 insertions(+), 34 deletions(-)
diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index 4f44d5c742..941bbff4fe 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -926,9 +926,7 @@ static int relinquish_memory(struct domain *d, struct
page_list_head *list)
*/
continue;
- if ( test_and_clear_bit(_PGC_allocated, &page->count_info) )
- put_page(page);
-
+ put_page_alloc_ref(page);
put_page(page);
if ( hypercall_preempt_check() )
diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 147f96a09e..e791d86892 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1939,8 +1939,7 @@ static int relinquish_memory(
BUG();
}
- if ( test_and_clear_bit(_PGC_allocated, &page->count_info) )
- put_page(page);
+ put_page_alloc_ref(page);
/*
* Forcibly invalidate top-most, still valid page tables at this point
diff --git a/xen/arch/x86/hvm/ioreq.c b/xen/arch/x86/hvm/ioreq.c
index 7a80cfb28b..a79cabb680 100644
--- a/xen/arch/x86/hvm/ioreq.c
+++ b/xen/arch/x86/hvm/ioreq.c
@@ -398,8 +398,7 @@ static int hvm_alloc_ioreq_mfn(struct hvm_ioreq_server *s,
bool buf)
return 0;
fail:
- if ( test_and_clear_bit(_PGC_allocated, &page->count_info) )
- put_page(page);
+ put_page_alloc_ref(page);
put_page_and_type(page);
return -ENOMEM;
@@ -418,13 +417,7 @@ static void hvm_free_ioreq_mfn(struct hvm_ioreq_server *s,
bool buf)
unmap_domain_page_global(iorp->va);
iorp->va = NULL;
- /*
- * Check whether we need to clear the allocation reference before
- * dropping the explicit references taken by get_page_and_type().
- */
- if ( test_and_clear_bit(_PGC_allocated, &page->count_info) )
- put_page(page);
-
+ put_page_alloc_ref(page);
put_page_and_type(page);
}
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index df2c0130f1..138662e777 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -498,8 +498,7 @@ void share_xen_page_with_guest(struct page_info *page,
struct domain *d,
void free_shared_domheap_page(struct page_info *page)
{
- if ( test_and_clear_bit(_PGC_allocated, &page->count_info) )
- put_page(page);
+ put_page_alloc_ref(page);
if ( !test_and_clear_bit(_PGC_xen_heap, &page->count_info) )
ASSERT_UNREACHABLE();
page->u.inuse.type_info = 0;
diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
index f16a3f5324..58d9157fa8 100644
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -1000,8 +1000,7 @@ static int share_pages(struct domain *sd, gfn_t sgfn,
shr_handle_t sh,
mem_sharing_page_unlock(firstpg);
/* Free the client page */
- if(test_and_clear_bit(_PGC_allocated, &cpage->count_info))
- put_page(cpage);
+ put_page_alloc_ref(cpage);
put_page(cpage);
/* We managed to free a domain page. */
@@ -1082,8 +1081,7 @@ int mem_sharing_add_to_physmap(struct domain *sd,
unsigned long sgfn, shr_handle
ret = -EOVERFLOW;
goto err_unlock;
}
- if ( test_and_clear_bit(_PGC_allocated, &cpage->count_info) )
- put_page(cpage);
+ put_page_alloc_ref(cpage);
put_page(cpage);
}
}
@@ -1177,8 +1175,7 @@ int __mem_sharing_unshare_page(struct domain *d,
domain_crash(d);
return -EOVERFLOW;
}
- if ( test_and_clear_bit(_PGC_allocated, &page->count_info) )
- put_page(page);
+ put_page_alloc_ref(page);
put_page(page);
}
put_gfn(d, gfn);
diff --git a/xen/arch/x86/mm/p2m-pod.c b/xen/arch/x86/mm/p2m-pod.c
index 4313863066..096e2773fb 100644
--- a/xen/arch/x86/mm/p2m-pod.c
+++ b/xen/arch/x86/mm/p2m-pod.c
@@ -274,9 +274,7 @@ p2m_pod_set_cache_target(struct p2m_domain *p2m, unsigned
long pod_target, int p
if ( test_and_clear_bit(_PGT_pinned, &(page+i)->u.inuse.type_info)
)
put_page_and_type(page + i);
- if ( test_and_clear_bit(_PGC_allocated, &(page+i)->count_info) )
- put_page(page + i);
-
+ put_page_alloc_ref(page + i);
put_page(page + i);
if ( preemptible && pod_target != p2m->pod.count &&
diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 4c9954867c..883352da7d 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -1609,8 +1609,7 @@ int p2m_mem_paging_evict(struct domain *d, unsigned long
gfn_l)
goto out_put;
/* Decrement guest domain's ref count of the page */
- if ( test_and_clear_bit(_PGC_allocated, &page->count_info) )
- put_page(page);
+ put_page_alloc_ref(page);
/* Remove mapping from p2m table */
ret = p2m_set_entry(p2m, gfn, INVALID_MFN, PAGE_ORDER_4K,
diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
index e6a0f30a4b..f0ca10a7fa 100644
--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -1707,8 +1707,7 @@ gnttab_unpopulate_status_frames(struct domain *d, struct
grant_table *gt)
}
BUG_ON(page_get_owner(pg) != d);
- if ( test_and_clear_bit(_PGC_allocated, &pg->count_info) )
- put_page(pg);
+ put_page_alloc_ref(pg);
if ( pg->count_info & ~PGC_xen_heap )
{
diff --git a/xen/common/memory.c b/xen/common/memory.c
index 03db7bfa9e..30d210fc08 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -388,9 +388,8 @@ int guest_remove_page(struct domain *d, unsigned long gmfn)
* For this purpose (and to match populate_physmap() behavior), the page
* is kept allocated.
*/
- if ( !rc && !is_domain_direct_mapped(d) &&
- test_and_clear_bit(_PGC_allocated, &page->count_info) )
- put_page(page);
+ if ( !rc && !is_domain_direct_mapped(d) )
+ put_page_alloc_ref(page);
put_page(page);
diff --git a/xen/common/xenoprof.c b/xen/common/xenoprof.c
index 8a72e382e6..4f3e799ebb 100644
--- a/xen/common/xenoprof.c
+++ b/xen/common/xenoprof.c
@@ -173,8 +173,7 @@ unshare_xenoprof_page_with_guest(struct xenoprof *x)
struct page_info *page = mfn_to_page(mfn_add(mfn, i));
BUG_ON(page_get_owner(page) != current->domain);
- if ( test_and_clear_bit(_PGC_allocated, &page->count_info) )
- put_page(page);
+ put_page_alloc_ref(page);
}
}
diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h
index a57974ae51..5d0c19f011 100644
--- a/xen/include/xen/mm.h
+++ b/xen/include/xen/mm.h
@@ -658,4 +658,18 @@ static inline void share_xen_page_with_privileged_guests(
share_xen_page_with_guest(page, dom_xen, flags);
}
+static inline void put_page_alloc_ref(struct page_info *page)
+{
+ /*
+ * Whenever a page is assigned to a domain then the _PGC_allocated bit
+ * is set and the reference count is set to at least 1. This function
+ * clears that 'allocation reference' but it is unsafe to do so without
+ * the caller holding an additional reference. I.e. the allocation
+ * reference must never be the last reference held.
+ */
+ BUG_ON((page->count_info & PGC_count_mask) <= 1);
+ if ( test_and_clear_bit(_PGC_allocated, &page->count_info) )
+ put_page(page);
+}
+
#endif /* __XEN_MM_H__ */
--
generated by git-patchbot for /home/xen/git/xen.git#master
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