Mailing List Archive

xen/arch/x86/mm/mem_sharing.c | 560 +++++++++++++++++++------------------
xen/include/asm-x86/mem_sharing.h | 19 +-
xen/include/asm-x86/mm.h | 11 +-
xen/include/public/domctl.h | 3 +
4 files changed, 322 insertions(+), 271 deletions(-)


The hashtable mechanism used by the sharing code is a bit odd. It seems
unnecessary and adds complexity. Instead, we replace this by storing a list
head directly in the page info for the case when the page is shared. This does
not add any extra space to the page_info and serves to remove significant
complexity from sharing.

Signed-off-by: Adin Scannell <adin@scannell.ca>
Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>

diff -r d29cba447de1 -r 4862cca21d3c xen/arch/x86/mm/mem_sharing.c
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -3,6 +3,7 @@
*
* Memory sharing support.
*
+ * Copyright (c) 2011 GridCentric, Inc. (Adin Scannell & Andres Lagar-Cavilla)
* Copyright (c) 2009 Citrix Systems, Inc. (Grzegorz Milos)
*
* This program is free software; you can redistribute it and/or modify
@@ -34,15 +35,29 @@

#include "mm-locks.h"

-/* Auditing of memory sharing code? */
-#define MEM_SHARING_AUDIT 0
-
#if MEM_SHARING_AUDIT
-static void mem_sharing_audit(void);
+static int mem_sharing_audit(void);
#define MEM_SHARING_DEBUG(_f, _a...) \
debugtrace_printk("mem_sharing_debug: %s(): " _f, __func__, ##_a)
+static struct list_head shr_audit_list;
+
+static inline void audit_add_list(struct page_info *page)
+{
+ list_add(&page->shared_info->entry, &shr_audit_list);
+}
+
+static inline void audit_del_list(struct page_info *page)
+{
+ list_del(&page->shared_info->entry);
+}
#else
-#define mem_sharing_audit() do {} while(0)
+static inline int mem_sharing_audit(void)
+{
+ return 0;
+}
+
+#define audit_add_list(p) ((void)0)
+#define audit_del_list(p) ((void)0)
#endif /* MEM_SHARING_AUDIT */

#define mem_sharing_enabled(d) \
@@ -58,17 +73,6 @@ static void mem_sharing_audit(void);
static shr_handle_t next_handle = 1;
static atomic_t nr_saved_mfns = ATOMIC_INIT(0);

-typedef struct shr_hash_entry
-{
- shr_handle_t handle;
- mfn_t mfn;
- struct shr_hash_entry *next;
- struct list_head gfns;
-} shr_hash_entry_t;
-
-#define SHR_HASH_LENGTH 1000
-static shr_hash_entry_t *shr_hash[SHR_HASH_LENGTH];
-
typedef struct gfn_info
{
unsigned long gfn;
@@ -89,36 +93,30 @@ static inline gfn_info_t *gfn_get_info(s
return list_entry(list->next, gfn_info_t, list);
}

-static void __init mem_sharing_hash_init(void)
+static inline gfn_info_t *mem_sharing_gfn_alloc(struct page_info *page,
+ struct domain *d,
+ unsigned long gfn)
{
- int i;
+ gfn_info_t *gfn_info = xmalloc(gfn_info_t);

- mm_lock_init(&shr_lock);
- for(i=0; i<SHR_HASH_LENGTH; i++)
- shr_hash[i] = NULL;
+ if ( gfn_info == NULL )
+ return NULL;
+
+ gfn_info->gfn = gfn;
+ gfn_info->domain = d->domain_id;
+ INIT_LIST_HEAD(&gfn_info->list);
+ list_add(&gfn_info->list, &page->shared_info->gfns);
+
+ return gfn_info;
}

-static shr_hash_entry_t *mem_sharing_hash_alloc(void)
-{
- return xmalloc(shr_hash_entry_t);
-}
-
-static void mem_sharing_hash_destroy(shr_hash_entry_t *e)
-{
- xfree(e);
-}
-
-static gfn_info_t *mem_sharing_gfn_alloc(void)
-{
- return xmalloc(gfn_info_t);
-}
-
-static void mem_sharing_gfn_destroy(gfn_info_t *gfn, int was_shared)
+static inline void mem_sharing_gfn_destroy(gfn_info_t *gfn_info,
+ int was_shared)
{
/* Decrement the number of pages, if the gfn was shared before */
if ( was_shared )
{
- struct domain *d = get_domain_by_id(gfn->domain);
+ struct domain *d = get_domain_by_id(gfn_info->domain);
/* Domain may have been destroyed by now *
* (if we are called from p2m_teardown) */
if ( d )
@@ -127,128 +125,127 @@ static void mem_sharing_gfn_destroy(gfn_
put_domain(d);
}
}
- xfree(gfn);
+
+ list_del(&gfn_info->list);
+ xfree(gfn_info);
}

-static shr_hash_entry_t* mem_sharing_hash_lookup(shr_handle_t handle)
+static struct page_info* mem_sharing_lookup(unsigned long mfn)
{
- shr_hash_entry_t *e;
-
- e = shr_hash[handle % SHR_HASH_LENGTH];
- while(e != NULL)
+ if ( mfn_valid(_mfn(mfn)) )
{
- if(e->handle == handle)
- return e;
- e = e->next;
+ struct page_info* page = mfn_to_page(_mfn(mfn));
+ if ( page_get_owner(page) == dom_cow )
+ {
+ ASSERT(page->u.inuse.type_info & PGT_type_mask);
+ ASSERT(get_gpfn_from_mfn(mfn) == SHARED_M2P_ENTRY);
+ return page;
+ }
}

return NULL;
}

-static shr_hash_entry_t* mem_sharing_hash_insert(shr_handle_t handle, mfn_t mfn)
+#if MEM_SHARING_AUDIT
+static int mem_sharing_audit(void)
{
- shr_hash_entry_t *e, **ee;
-
- e = mem_sharing_hash_alloc();
- if(e == NULL) return NULL;
- e->handle = handle;
- e->mfn = mfn;
- ee = &shr_hash[handle % SHR_HASH_LENGTH];
- e->next = *ee;
- *ee = e;
- return e;
-}
-
-static void mem_sharing_hash_delete(shr_handle_t handle)
-{
- shr_hash_entry_t **pprev, *e;
-
- pprev = &shr_hash[handle % SHR_HASH_LENGTH];
- e = *pprev;
- while(e != NULL)
- {
- if(e->handle == handle)
- {
- *pprev = e->next;
- mem_sharing_hash_destroy(e);
- return;
- }
- pprev = &e->next;
- e = e->next;
- }
- printk("Could not find shr entry for handle %"PRIx64"\n", handle);
- BUG();
-}
-
-#if MEM_SHARING_AUDIT
-static void mem_sharing_audit(void)
-{
- shr_hash_entry_t *e;
- struct list_head *le;
- gfn_info_t *g;
- int bucket;
- struct page_info *pg;
+ int errors = 0;
+ struct list_head *ae;

ASSERT(shr_locked_by_me());

- for(bucket=0; bucket < SHR_HASH_LENGTH; bucket++)
+ list_for_each(ae, &shr_audit_list)
{
- e = shr_hash[bucket];
- /* Loop over all shr_hash_entries */
- while(e != NULL)
+ struct page_sharing_info *shared_info;
+ unsigned long nr_gfns = 0;
+ struct page_info *pg;
+ struct list_head *le;
+ mfn_t mfn;
+
+ shared_info = list_entry(ae, struct page_sharing_info, entry);
+ pg = shared_info->pg;
+ mfn = page_to_mfn(pg);
+
+ /* Check if the MFN has correct type, owner and handle. */
+ if ( !(pg->u.inuse.type_info & PGT_shared_page) )
{
- int nr_gfns=0;
+ MEM_SHARING_DEBUG("mfn %lx in audit list, but not PGT_shared_page (%d)!\n",
+ mfn_x(mfn), pg->u.inuse.type_info & PGT_type_mask);
+ errors++;
+ continue;
+ }

- /* Check if the MFN has correct type, owner and handle */
- pg = mfn_to_page(e->mfn);
- if((pg->u.inuse.type_info & PGT_type_mask) != PGT_shared_page)
- MEM_SHARING_DEBUG("mfn %lx not shared, but in the hash!\n",
- mfn_x(e->mfn));
- if(page_get_owner(pg) != dom_cow)
- MEM_SHARING_DEBUG("mfn %lx shared, but wrong owner (%d)!\n",
- mfn_x(e->mfn),
- page_get_owner(pg)->domain_id);
- if(e->handle != pg->shr_handle)
- MEM_SHARING_DEBUG("mfn %lx shared, but wrong handle "
- "(%ld != %ld)!\n",
- mfn_x(e->mfn), pg->shr_handle, e->handle);
- /* Check if all GFNs map to the MFN, and the p2m types */
- list_for_each(le, &e->gfns)
+ /* Check the page owner. */
+ if ( page_get_owner(pg) != dom_cow )
+ {
+ MEM_SHARING_DEBUG("mfn %lx shared, but wrong owner (%d)!\n",
+ mfn_x(mfn), page_get_owner(pg)->domain_id);
+ errors++;
+ }
+
+ /* Check the m2p entry */
+ if ( get_gpfn_from_mfn(mfn_x(mfn)) != SHARED_M2P_ENTRY )
+ {
+ MEM_SHARING_DEBUG("mfn %lx shared, but wrong m2p entry (%lx)!\n",
+ mfn_x(mfn), get_gpfn_from_mfn(mfn_x(mfn)));
+ errors++;
+ }
+
+ /* Check we have a list */
+ if ( (!pg->shared_info) || (list_empty(&pg->shared_info->gfns)) )
+ {
+ MEM_SHARING_DEBUG("mfn %lx shared, but empty gfn list!\n",
+ mfn_x(mfn));
+ errors++;
+ continue;
+ }
+
+ /* Check if all GFNs map to the MFN, and the p2m types */
+ list_for_each(le, &pg->shared_info->gfns)
+ {
+ struct domain *d;
+ p2m_type_t t;
+ mfn_t o_mfn;
+ gfn_info_t *g;
+
+ g = list_entry(le, gfn_info_t, list);
+ d = get_domain_by_id(g->domain);
+ if ( d == NULL )
{
- struct domain *d;
- p2m_type_t t;
- mfn_t mfn;
-
- g = list_entry(le, struct gfn_info, list);
- d = get_domain_by_id(g->domain);
- if(d == NULL)
- {
- MEM_SHARING_DEBUG("Unknow dom: %d, for PFN=%lx, MFN=%lx\n",
- g->domain, g->gfn, mfn_x(e->mfn));
- continue;
- }
- mfn = get_gfn_unlocked(d, g->gfn, &t);
- if(mfn_x(mfn) != mfn_x(e->mfn))
- MEM_SHARING_DEBUG("Incorrect P2M for d=%d, PFN=%lx."
- "Expecting MFN=%ld, got %ld\n",
- g->domain, g->gfn, mfn_x(e->mfn),
- mfn_x(mfn));
- if(t != p2m_ram_shared)
- MEM_SHARING_DEBUG("Incorrect P2M type for d=%d, PFN=%lx."
- "Expecting t=%d, got %d\n",
- g->domain, g->gfn, mfn_x(e->mfn),
- p2m_ram_shared, t);
- put_domain(d);
- nr_gfns++;
- }
- if(nr_gfns != (pg->u.inuse.type_info & PGT_count_mask))
- MEM_SHARING_DEBUG("Mismatched counts for MFN=%lx."
- "nr_gfns in hash %d, in type_info %d\n",
- mfn_x(e->mfn), nr_gfns,
- (pg->u.inuse.type_info & PGT_count_mask));
- e = e->next;
+ MEM_SHARING_DEBUG("Unknown dom: %d, for PFN=%lx, MFN=%lx\n",
+ g->domain, g->gfn, mfn);
+ errors++;
+ continue;
+ }
+ o_mfn = get_gfn_query_unlocked(d, g->gfn, &t);
+ if ( mfn_x(o_mfn) != mfn_x(mfn) )
+ {
+ MEM_SHARING_DEBUG("Incorrect P2M for d=%d, PFN=%lx."
+ "Expecting MFN=%ld, got %ld\n",
+ g->domain, g->gfn, mfn, mfn_x(o_mfn));
+ errors++;
+ }
+ if ( t != p2m_ram_shared )
+ {
+ MEM_SHARING_DEBUG("Incorrect P2M type for d=%d, PFN=%lx."
+ "Expecting t=%d, got %d\n",
+ g->domain, g->gfn, mfn, p2m_ram_shared, t);
+ errors++;
+ }
+ put_domain(d);
+ nr_gfns++;
+ }
+ if ( nr_gfns != (pg->u.inuse.type_info & PGT_count_mask) )
+ {
+ MEM_SHARING_DEBUG("Mismatched counts for MFN=%lx."
+ "nr_gfns in hash %d, in type_info %d\n",
+ mfn_x(mfn), nr_gfns,
+ (pg->u.inuse.type_info & PGT_count_mask));
+ errors++;
}
}
+
+ return errors;
}
#endif

@@ -391,36 +388,6 @@ static int mem_sharing_gref_to_gfn(struc
return 0;
}

-/* Account for a GFN being shared/unshared.
- * When sharing this function needs to be called _before_ gfn lists are merged
- * together, but _after_ gfn is removed from the list when unsharing.
- */
-static int mem_sharing_gfn_account(struct gfn_info *gfn, int sharing)
-{
- struct domain *d;
-
- /* A) When sharing:
- * if the gfn being shared is in > 1 long list, its already been
- * accounted for
- * B) When unsharing:
- * if the list is longer than > 1, we don't have to account yet.
- */
- if(list_has_one_entry(&gfn->list))
- {
- d = get_domain_by_id(gfn->domain);
- BUG_ON(!d);
- if(sharing)
- atomic_inc(&d->shr_pages);
- else
- atomic_dec(&d->shr_pages);
- put_domain(d);
-
- return 1;
- }
- mem_sharing_audit();
-
- return 0;
-}

int mem_sharing_debug_gref(struct domain *d, grant_ref_t ref)
{
@@ -458,8 +425,6 @@ int mem_sharing_nominate_page(struct dom
mfn_t mfn;
struct page_info *page;
int ret;
- shr_handle_t handle;
- shr_hash_entry_t *hash_entry;
struct gfn_info *gfn_info;

*phandle = 0UL;
@@ -475,7 +440,7 @@ int mem_sharing_nominate_page(struct dom
/* Return the handle if the page is already shared */
page = mfn_to_page(mfn);
if ( p2m_is_shared(p2mt) ) {
- *phandle = page->shr_handle;
+ *phandle = page->shared_info->handle;
ret = 0;
goto out;
}
@@ -489,16 +454,29 @@ int mem_sharing_nominate_page(struct dom
if ( ret )
goto out;

- /* Create the handle */
+ /* Initialize the shared state */
ret = -ENOMEM;
- handle = next_handle++;
- if((hash_entry = mem_sharing_hash_insert(handle, mfn)) == NULL)
+ if ( (page->shared_info =
+ xmalloc(struct page_sharing_info)) == NULL )
{
+ BUG_ON(page_make_private(d, page) != 0);
goto out;
}
- if((gfn_info = mem_sharing_gfn_alloc()) == NULL)
+ page->shared_info->pg = page;
+ INIT_LIST_HEAD(&page->shared_info->gfns);
+#if MEM_SHARING_AUDIT
+ INIT_LIST_HEAD(&page->shared_info->entry);
+#endif
+
+ /* Create the handle */
+ page->shared_info->handle = next_handle++;
+
+ /* Create the local gfn info */
+ if ( (gfn_info = mem_sharing_gfn_alloc(page, d, gfn)) == NULL )
{
- mem_sharing_hash_destroy(hash_entry);
+ xfree(page->shared_info);
+ page->shared_info = NULL;
+ BUG_ON(page_make_private(d, page) != 0);
goto out;
}

@@ -509,23 +487,19 @@ int mem_sharing_nominate_page(struct dom
* it a few lines above.
* The mfn needs to revert back to rw type. This should never fail,
* since no-one knew that the mfn was temporarily sharable */
+ mem_sharing_gfn_destroy(gfn_info, 0);
+ xfree(page->shared_info);
+ page->shared_info = NULL;
+ /* NOTE: We haven't yet added this to the audit list. */
BUG_ON(page_make_private(d, page) != 0);
- mem_sharing_hash_destroy(hash_entry);
- mem_sharing_gfn_destroy(gfn_info, 0);
goto out;
}

/* Update m2p entry to SHARED_M2P_ENTRY */
set_gpfn_from_mfn(mfn_x(mfn), SHARED_M2P_ENTRY);

- INIT_LIST_HEAD(&hash_entry->gfns);
- INIT_LIST_HEAD(&gfn_info->list);
- list_add(&gfn_info->list, &hash_entry->gfns);
- gfn_info->gfn = gfn;
- gfn_info->domain = d->domain_id;
- page->shr_handle = handle;
- *phandle = handle;
-
+ *phandle = page->shared_info->handle;
+ audit_add_list(page);
ret = 0;

out:
@@ -534,54 +508,92 @@ out:
return ret;
}

-int mem_sharing_share_pages(shr_handle_t sh, shr_handle_t ch)
+int mem_sharing_share_pages(struct domain *sd, unsigned long sgfn, shr_handle_t sh,
+ struct domain *cd, unsigned long cgfn, shr_handle_t ch)
{
- shr_hash_entry_t *se, *ce;
struct page_info *spage, *cpage;
struct list_head *le, *te;
- struct gfn_info *gfn;
+ gfn_info_t *gfn;
struct domain *d;
- int ret;
+ int ret = -EINVAL, single_client_gfn, single_source_gfn;
+ mfn_t smfn, cmfn;
+ p2m_type_t smfn_type, cmfn_type;

shr_lock();

+ /* XXX if sd == cd handle potential deadlock by ordering
+ * the get_ and put_gfn's */
+ smfn = get_gfn(sd, sgfn, &smfn_type);
+ cmfn = get_gfn(cd, cgfn, &cmfn_type);
+
ret = XEN_DOMCTL_MEM_SHARING_S_HANDLE_INVALID;
- se = mem_sharing_hash_lookup(sh);
- if(se == NULL) goto err_out;
+ spage = mem_sharing_lookup(mfn_x(smfn));
+ if ( spage == NULL )
+ goto err_out;
+ ASSERT(smfn_type == p2m_ram_shared);
ret = XEN_DOMCTL_MEM_SHARING_C_HANDLE_INVALID;
- ce = mem_sharing_hash_lookup(ch);
- if(ce == NULL) goto err_out;
- spage = mfn_to_page(se->mfn);
- cpage = mfn_to_page(ce->mfn);
- /* gfn lists always have at least one entry => save to call list_entry */
- mem_sharing_gfn_account(gfn_get_info(&ce->gfns), 1);
- mem_sharing_gfn_account(gfn_get_info(&se->gfns), 1);
- list_for_each_safe(le, te, &ce->gfns)
+ cpage = mem_sharing_lookup(mfn_x(cmfn));
+ if ( cpage == NULL )
+ goto err_out;
+ ASSERT(cmfn_type == p2m_ram_shared);
+
+ /* Check that the handles match */
+ if ( spage->shared_info->handle != sh )
{
- gfn = list_entry(le, struct gfn_info, list);
- /* Get the source page and type, this should never fail
- * because we are under shr lock, and got non-null se */
+ ret = XEN_DOMCTL_MEM_SHARING_S_HANDLE_INVALID;
+ goto err_out;
+ }
+ if ( cpage->shared_info->handle != ch )
+ {
+ ret = XEN_DOMCTL_MEM_SHARING_C_HANDLE_INVALID;
+ goto err_out;
+ }
+
+ /* Merge the lists together */
+ single_source_gfn = list_has_one_entry(&spage->shared_info->gfns);
+ single_client_gfn = list_has_one_entry(&cpage->shared_info->gfns);
+ list_for_each_safe(le, te, &cpage->shared_info->gfns)
+ {
+ gfn = list_entry(le, gfn_info_t, list);
+ /* Get the source page and type, this should never fail:
+ * we are under shr lock, and got a successful lookup */
BUG_ON(!get_page_and_type(spage, dom_cow, PGT_shared_page));
- /* Move the gfn_info from ce list to se list */
+ /* Move the gfn_info from client list to source list */
list_del(&gfn->list);
+ list_add(&gfn->list, &spage->shared_info->gfns);
+ put_page_and_type(cpage);
d = get_domain_by_id(gfn->domain);
BUG_ON(!d);
- BUG_ON(set_shared_p2m_entry(d, gfn->gfn, se->mfn) == 0);
+ BUG_ON(set_shared_p2m_entry(d, gfn->gfn, smfn) == 0);
+ if ( single_client_gfn )
+ {
+ /* Only increase the per-domain count when we are actually
+ * sharing. And don't increase it should we ever re-share */
+ atomic_inc(&d->shr_pages);
+ ASSERT( cd == d );
+ }
put_domain(d);
- list_add(&gfn->list, &se->gfns);
- put_page_and_type(cpage);
- }
- ASSERT(list_empty(&ce->gfns));
- mem_sharing_hash_delete(ch);
- atomic_inc(&nr_saved_mfns);
+ }
+ ASSERT(list_empty(&cpage->shared_info->gfns));
+ if ( single_source_gfn )
+ atomic_inc(&sd->shr_pages);
+
+ /* Clear the rest of the shared state */
+ audit_del_list(cpage);
+ xfree(cpage->shared_info);
+ cpage->shared_info = NULL;
+
/* Free the client page */
if(test_and_clear_bit(_PGC_allocated, &cpage->count_info))
put_page(cpage);
+
+ atomic_inc(&nr_saved_mfns);
ret = 0;

err_out:
+ put_gfn(cd, cgfn);
+ put_gfn(sd, sgfn);
shr_unlock();
-
return ret;
}

@@ -593,13 +605,9 @@ int mem_sharing_unshare_page(struct doma
mfn_t mfn;
struct page_info *page, *old_page;
void *s, *t;
- int ret, last_gfn;
- shr_hash_entry_t *hash_entry;
- struct gfn_info *gfn_info = NULL;
- shr_handle_t handle;
+ int last_gfn;
+ gfn_info_t *gfn_info = NULL;
struct list_head *le;
-
- /* Remove the gfn_info from the list */

/* This is one of the reasons why we can't enforce ordering
* between shr_lock and p2m fine-grained locks in mm-lock.
@@ -615,56 +623,74 @@ int mem_sharing_unshare_page(struct doma
return 0;
}

- page = mfn_to_page(mfn);
- handle = page->shr_handle;
-
- hash_entry = mem_sharing_hash_lookup(handle);
- list_for_each(le, &hash_entry->gfns)
+ page = mem_sharing_lookup(mfn_x(mfn));
+ if ( page == NULL )
{
- gfn_info = list_entry(le, struct gfn_info, list);
+ gdprintk(XENLOG_ERR, "Domain p2m is shared, but page is not: "
+ "%lx\n", gfn);
+ BUG();
+ }
+
+ list_for_each(le, &page->shared_info->gfns)
+ {
+ gfn_info = list_entry(le, gfn_info_t, list);
if ( (gfn_info->gfn == gfn) && (gfn_info->domain == d->domain_id) )
goto gfn_found;
}
gdprintk(XENLOG_ERR, "Could not find gfn_info for shared gfn: "
"%lx\n", gfn);
BUG();
-gfn_found:
- /* Delete gfn_info from the list, but hold on to it, until we've allocated
- * memory to make a copy */
- list_del(&gfn_info->list);
- last_gfn = list_empty(&hash_entry->gfns);
+
+gfn_found:
+ /* Do the accounting first. If anything fails below, we have bigger
+ * bigger fish to fry. First, remove the gfn from the list. */
+ last_gfn = list_has_one_entry(&page->shared_info->gfns);
+ mem_sharing_gfn_destroy(gfn_info, !last_gfn);
+ if ( !last_gfn )
+ {
+ atomic_dec(&nr_saved_mfns);
+ /* Update stats if only one gfn is left for this shared page.
+ * This really isn't a shared page anymore. */
+ if ( list_has_one_entry(&page->shared_info->gfns) )
+ {
+ struct list_head *pos = page->shared_info->gfns.next;
+ gfn_info_t *gfn_info = list_entry(pos, gfn_info_t, list);
+ struct domain *d = get_domain_by_id(gfn_info->domain);
+ BUG_ON(!d);
+ atomic_dec(&d->shr_pages);
+ put_domain(d);
+ }
+ } else {
+ /* Clean up shared state */
+ audit_del_list(page);
+ xfree(page->shared_info);
+ page->shared_info = NULL;
+ }

/* If the GFN is getting destroyed drop the references to MFN
* (possibly freeing the page), and exit early */
if ( flags & MEM_SHARING_DESTROY_GFN )
{
- mem_sharing_gfn_destroy(gfn_info, !last_gfn);
- if(last_gfn)
- mem_sharing_hash_delete(handle);
- else
- /* Even though we don't allocate a private page, we have to account
- * for the MFN that originally backed this PFN. */
- atomic_dec(&nr_saved_mfns);
put_gfn(d, gfn);
shr_unlock();
put_page_and_type(page);
- if(last_gfn &&
- test_and_clear_bit(_PGC_allocated, &page->count_info))
+ if( last_gfn &&
+ test_and_clear_bit(_PGC_allocated, &page->count_info))
put_page(page);
+
return 0;
}

- ret = page_make_private(d, page);
- BUG_ON(last_gfn & ret);
- if(ret == 0) goto private_page_found;
+ if ( last_gfn )
+ {
+ BUG_ON(page_make_private(d, page) != 0);
+ goto private_page_found;
+ }

old_page = page;
page = mem_sharing_alloc_page(d, gfn);
- if(!page)
+ if ( !page )
{
- /* We've failed to obtain memory for private page. Need to re-add the
- * gfn_info to relevant list */
- list_add(&gfn_info->list, &hash_entry->gfns);
put_gfn(d, gfn);
shr_unlock();
return -ENOMEM;
@@ -676,30 +702,18 @@ gfn_found:
unmap_domain_page(s);
unmap_domain_page(t);

- /* NOTE: set_shared_p2m_entry will switch the underlying mfn. If
- * we do get_page withing get_gfn, the correct sequence here
- * should be
- get_page(page);
- put_page(old_page);
- * so that the ref to the old page is dropped, and a ref to
- * the new page is obtained to later be dropped in put_gfn */
BUG_ON(set_shared_p2m_entry(d, gfn, page_to_mfn(page)) == 0);
put_page_and_type(old_page);

private_page_found:
- /* We've got a private page, we can commit the gfn destruction */
- mem_sharing_gfn_destroy(gfn_info, !last_gfn);
- if(last_gfn)
- mem_sharing_hash_delete(handle);
- else
- atomic_dec(&nr_saved_mfns);
-
if ( p2m_change_type(d, gfn, p2m_ram_shared, p2m_ram_rw) !=
p2m_ram_shared )
{
- printk("Could not change p2m type.\n");
+ gdprintk(XENLOG_ERR, "Could not change p2m type d %hu gfn %lx.\n",
+ d->domain_id, gfn);
BUG();
}
+
/* Update m2p entry */
set_gpfn_from_mfn(mfn_x(page_to_mfn(page)), gfn);

@@ -756,9 +770,18 @@ int mem_sharing_domctl(struct domain *d,

case XEN_DOMCTL_MEM_EVENT_OP_SHARING_SHARE:
{
- shr_handle_t sh = mec->u.share.source_handle;
- shr_handle_t ch = mec->u.share.client_handle;
- rc = mem_sharing_share_pages(sh, ch);
+ unsigned long sgfn = mec->u.share.source_gfn;
+ shr_handle_t sh = mec->u.share.source_handle;
+ struct domain *cd = get_domain_by_id(mec->u.share.client_domain);
+ if ( cd )
+ {
+ unsigned long cgfn = mec->u.share.client_gfn;
+ shr_handle_t ch = mec->u.share.client_handle;
+ rc = mem_sharing_share_pages(d, sgfn, sh, cd, cgfn, ch);
+ put_domain(cd);
+ }
+ else
+ return -EEXIST;
}
break;

@@ -806,6 +829,9 @@ int mem_sharing_domctl(struct domain *d,
void __init mem_sharing_init(void)
{
printk("Initing memory sharing.\n");
- mem_sharing_hash_init();
+ mm_lock_init(&shr_lock);
+#if MEM_SHARING_AUDIT
+ INIT_LIST_HEAD(&shr_audit_list);
+#endif
}

diff -r d29cba447de1 -r 4862cca21d3c xen/include/asm-x86/mem_sharing.h
--- a/xen/include/asm-x86/mem_sharing.h
+++ b/xen/include/asm-x86/mem_sharing.h
@@ -22,13 +22,28 @@
#ifndef __MEM_SHARING_H__
#define __MEM_SHARING_H__

+#include <public/domctl.h>
+
+/* Auditing of memory sharing code? */
+#define MEM_SHARING_AUDIT 0
+
+typedef uint64_t shr_handle_t;
+
+struct page_sharing_info
+{
+ struct page_info *pg; /* Back pointer to the page. */
+ shr_handle_t handle; /* Globally unique version / handle. */
+#if MEM_SHARING_AUDIT
+ struct list_head entry; /* List of all shared pages (entry). */
+#endif
+ struct list_head gfns; /* List of domains and gfns for this page (head). */
+};
+
#ifdef __x86_64__

#define sharing_supported(_d) \
(is_hvm_domain(_d) && paging_mode_hap(_d))

-typedef uint64_t shr_handle_t;
-
unsigned int mem_sharing_get_nr_saved_mfns(void);
int mem_sharing_nominate_page(struct domain *d,
unsigned long gfn,
diff -r d29cba447de1 -r 4862cca21d3c xen/include/asm-x86/mm.h
--- a/xen/include/asm-x86/mm.h
+++ b/xen/include/asm-x86/mm.h
@@ -31,6 +31,8 @@ struct page_list_entry
__pdx_t next, prev;
};

+struct page_sharing_info;
+
struct page_info
{
union {
@@ -49,8 +51,13 @@ struct page_info
/* For non-pinnable single-page shadows, a higher entry that points
* at us. */
paddr_t up;
- /* For shared/sharable pages the sharing handle */
- uint64_t shr_handle;
+ /* For shared/sharable pages, we use a doubly-linked list
+ * of all the {pfn,domain} pairs that map this page. We also include
+ * an opaque handle, which is effectively a version, so that clients
+ * of sharing share the version they expect to.
+ * This list is allocated and freed when a page is shared/unshared.
+ */
+ struct page_sharing_info *shared_info;
};

/* Reference count and various PGC_xxx flags and fields. */
diff -r d29cba447de1 -r 4862cca21d3c xen/include/public/domctl.h
--- a/xen/include/public/domctl.h
+++ b/xen/include/public/domctl.h
@@ -789,7 +789,10 @@ struct xen_domctl_mem_sharing_op {
uint64_aligned_t handle; /* OUT: the handle */
} nominate;
struct mem_sharing_op_share { /* OP_SHARE */
+ uint64_aligned_t source_gfn; /* IN: the gfn of the source page */
uint64_aligned_t source_handle; /* IN: handle to the source page */
+ uint64_aligned_t client_domain; /* IN: the client domain id */
+ uint64_aligned_t client_gfn; /* IN: the client gfn */
uint64_aligned_t client_handle; /* IN: handle to the client page */
} share;
struct mem_sharing_op_debug { /* OP_DEBUG_xxx */

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