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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH v4 5/7] mm: make MEMF_no_refcount pages safe to assign
Currently it is unsafe to assign a domheap page allocated with
MEMF_no_refcount to a domain because the domain't 'tot_pages' will not
be incremented, but will be decrement when the page is freed (since
free_domheap_pages() has no way of telling that the increment was skipped).
This patch allocates a new 'count_info' bit for a PGC_no_refcount flag
which is then used to mark domheap pages allocated with MEMF_no_refcount.
This then allows free_domheap_pages() to skip decrementing tot_pages when
appropriate and hence makes the pages safe to assign.
NOTE: The patch sets MEMF_no_refcount directly in alloc_domheap_pages()
rather than in assign_pages() because the latter is called with
MEMF_no_refcount by memory_exchange() as an optimization, to avoid
too many calls to domain_adjust_tot_pages() (which acquires and
releases the global 'heap_lock').
Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
---
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Julien Grall <julien@xxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Wei Liu <wl@xxxxxxx>
Cc: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
Cc: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>
v4:
- New in v4
---
xen/common/page_alloc.c | 39 ++++++++++++++++++++++++++++-----------
xen/include/asm-arm/mm.h | 5 ++++-
xen/include/asm-x86/mm.h | 7 +++++--
3 files changed, 37 insertions(+), 14 deletions(-)
diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 919a270587..6103f14a4e 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -460,6 +460,9 @@ unsigned long domain_adjust_tot_pages(struct domain *d,
long pages)
{
long dom_before, dom_after, dom_claimed, sys_before, sys_after;
+ if ( !pages )
+ goto out;
+
ASSERT(spin_is_locked(&d->page_alloc_lock));
d->tot_pages += pages;
@@ -1389,6 +1392,8 @@ static void free_heap_pages(
for ( i = 0; i < (1 << order); i++ )
{
+ ASSERT(!(pg[i].count_info & PGC_no_refcount));
+
/*
* Cannot assume that count_info == 0, as there are some corner cases
* where it isn't the case and yet it isn't a bug:
@@ -2314,11 +2319,6 @@ struct page_info *alloc_domheap_pages(
if ( memflags & MEMF_no_owner )
memflags |= MEMF_no_refcount;
- else if ( (memflags & MEMF_no_refcount) && d )
- {
- ASSERT(!(memflags & MEMF_no_refcount));
- return NULL;
- }
if ( !dma_bitsize )
memflags &= ~MEMF_no_dma;
@@ -2331,11 +2331,20 @@ struct page_info *alloc_domheap_pages(
memflags, d)) == NULL)) )
return NULL;
- if ( d && !(memflags & MEMF_no_owner) &&
- assign_pages(d, pg, order, memflags) )
+ if ( d && !(memflags & MEMF_no_owner) )
{
- free_heap_pages(pg, order, memflags & MEMF_no_scrub);
- return NULL;
+ if ( assign_pages(d, pg, order, memflags) )
+ {
+ free_heap_pages(pg, order, memflags & MEMF_no_scrub);
+ return NULL;
+ }
+ if ( memflags & MEMF_no_refcount )
+ {
+ unsigned long i;
+
+ for ( i = 0; i < (1 << order); i++ )
+ pg[i].count_info |= PGC_no_refcount;
+ }
}
return pg;
@@ -2368,24 +2377,32 @@ void free_domheap_pages(struct page_info *pg, unsigned
int order)
if ( likely(d) && likely(d != dom_cow) )
{
+ long pages = 0;
+
/* NB. May recursively lock from relinquish_memory(). */
spin_lock_recursive(&d->page_alloc_lock);
for ( i = 0; i < (1 << order); i++ )
{
+ unsigned long count_info = pg[i].count_info;
+
if ( pg[i].u.inuse.type_info & PGT_count_mask )
{
printk(XENLOG_ERR
"pg[%u] MFN %"PRI_mfn" c=%#lx o=%u v=%#lx t=%#x\n",
i, mfn_x(page_to_mfn(pg + i)),
- pg[i].count_info, pg[i].v.free.order,
+ count_info, pg[i].v.free.order,
pg[i].u.free.val, pg[i].tlbflush_timestamp);
BUG();
}
arch_free_heap_page(d, &pg[i]);
+ if ( count_info & PGC_no_refcount )
+ pg[i].count_info &= ~PGC_no_refcount;
+ else
+ pages--;
}
- drop_dom_ref = !domain_adjust_tot_pages(d, -(1 << order));
+ drop_dom_ref = !domain_adjust_tot_pages(d, pages);
spin_unlock_recursive(&d->page_alloc_lock);
diff --git a/xen/include/asm-arm/mm.h b/xen/include/asm-arm/mm.h
index 333efd3a60..1076cc9713 100644
--- a/xen/include/asm-arm/mm.h
+++ b/xen/include/asm-arm/mm.h
@@ -119,9 +119,12 @@ struct page_info
#define PGC_state_offlined PG_mask(2, 9)
#define PGC_state_free PG_mask(3, 9)
#define page_state_is(pg, st) (((pg)->count_info&PGC_state) == PGC_state_##st)
+/* Page is not reference counted */
+#define _PGC_no_refcount PG_shift(10)
+#define PGC_no_refcount PG_mask(1, 10)
/* Count of references to this frame. */
-#define PGC_count_width PG_shift(9)
+#define PGC_count_width PG_shift(10)
#define PGC_count_mask ((1UL<<PGC_count_width)-1)
/*
diff --git a/xen/include/asm-x86/mm.h b/xen/include/asm-x86/mm.h
index 2ca8882ad0..e75feea15e 100644
--- a/xen/include/asm-x86/mm.h
+++ b/xen/include/asm-x86/mm.h
@@ -77,9 +77,12 @@
#define PGC_state_offlined PG_mask(2, 9)
#define PGC_state_free PG_mask(3, 9)
#define page_state_is(pg, st) (((pg)->count_info&PGC_state) == PGC_state_##st)
+/* Page is not reference counted */
+#define _PGC_no_refcount PG_shift(10)
+#define PGC_no_refcount PG_mask(1, 10)
- /* Count of references to this frame. */
-#define PGC_count_width PG_shift(9)
+/* Count of references to this frame. */
+#define PGC_count_width PG_shift(10)
#define PGC_count_mask ((1UL<<PGC_count_width)-1)
/*
--
2.20.1
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