# HG changeset patch
# User Olaf Hering <olaf@xxxxxxxxx>
# Date 1318336551 -7200
# Node ID bdd49540f1e1c803d01c88adb67c6ce01e2d00d8
# Parent 4b0907c6a08c348962bd976c2976257b412408be
xenpaging: handle evict failures
Evict of a nominated gfn must fail if some other process mapped the
page without checking the p2mt of that gfn first.
Add a check to cancel eviction if the page usage count is not 1.
Handle the possible eviction failure in the page-in paths.
After nominate and before evict, something may check the p2mt and call
populate. Handle this case and let the gfn enter the page-in path. The
gfn may still be connected to a mfn, so there is no need to allocate a
new page in prep.
Adjust do_mmu_update to return -ENOENT only if the gfn has entered the
page-in path and if it is not yet connected to a mfn. Otherwise
linux_privcmd_map_foreign_bulk() may loop forever.
Add MEM_EVENT_FLAG_EVICT_FAIL to inform pager that a page-in request for
a possible not-evicted page was sent. xenpaging does currently not need
that flag because failure to evict a gfn will be caught.
Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
diff -r 4b0907c6a08c -r bdd49540f1e1 tools/xenpaging/xenpaging.c
--- a/tools/xenpaging/xenpaging.c
+++ b/tools/xenpaging/xenpaging.c
@@ -734,10 +734,12 @@ int main(int argc, char *argv[])
}
else
{
- DPRINTF("page already populated (domain = %d; vcpu = %d;"
- " gfn = %"PRIx64"; paused = %d)\n",
- paging->mem_event.domain_id, req.vcpu_id,
- req.gfn, req.flags & MEM_EVENT_FLAG_VCPU_PAUSED);
+ DPRINTF("page %s populated (domain = %d; vcpu = %d;"
+ " gfn = %"PRIx64"; paused = %d; evict_fail = %d)\n",
+ req.flags & MEM_EVENT_FLAG_EVICT_FAIL ? "not" :
"already",
+ paging->mem_event.domain_id, req.vcpu_id, req.gfn,
+ !!(req.flags & MEM_EVENT_FLAG_VCPU_PAUSED) ,
+ !!(req.flags & MEM_EVENT_FLAG_EVICT_FAIL) );
/* Tell Xen to resume the vcpu */
/* XXX: Maybe just check if the vcpu was paused? */
diff -r 4b0907c6a08c -r bdd49540f1e1 xen/arch/x86/mm.c
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -3532,7 +3532,7 @@ int do_mmu_update(
rc = -ENOENT;
break;
}
- else if ( p2m_ram_paging_in_start == l1e_p2mt )
+ else if ( p2m_ram_paging_in_start == l1e_p2mt &&
!mfn_valid(mfn) )
{
rc = -ENOENT;
break;
@@ -3572,7 +3572,7 @@ int do_mmu_update(
rc = -ENOENT;
break;
}
- else if ( p2m_ram_paging_in_start == l2e_p2mt )
+ else if ( p2m_ram_paging_in_start == l2e_p2mt &&
!mfn_valid(mfn) )
{
rc = -ENOENT;
break;
@@ -3600,7 +3600,7 @@ int do_mmu_update(
rc = -ENOENT;
break;
}
- else if ( p2m_ram_paging_in_start == l3e_p2mt )
+ else if ( p2m_ram_paging_in_start == l3e_p2mt &&
!mfn_valid(mfn) )
{
rc = -ENOENT;
break;
@@ -3628,7 +3628,7 @@ int do_mmu_update(
rc = -ENOENT;
break;
}
- else if ( p2m_ram_paging_in_start == l4e_p2mt )
+ else if ( p2m_ram_paging_in_start == l4e_p2mt &&
!mfn_valid(mfn) )
{
rc = -ENOENT;
break;
diff -r 4b0907c6a08c -r bdd49540f1e1 xen/arch/x86/mm/p2m.c
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -731,15 +731,24 @@ int p2m_mem_paging_evict(struct domain *
if ( unlikely(!mfn_valid(mfn)) )
goto out;
- if ( (p2mt == p2m_ram_paged) || (p2mt == p2m_ram_paging_in) ||
- (p2mt == p2m_ram_paging_in_start) )
+ /* Allow only nominated pages */
+ if ( p2mt != p2m_ram_paging_out )
goto out;
+ ret = -EBUSY;
/* Get the page so it doesn't get modified under Xen's feet */
page = mfn_to_page(mfn);
if ( unlikely(!get_page(page, d)) )
goto out;
+ /* Check page count and type once more */
+ if ( (page->count_info & (PGC_count_mask | PGC_allocated)) !=
+ (2 | PGC_allocated) )
+ goto out_put;
+
+ if ( (page->u.inuse.type_info & PGT_type_mask) != PGT_none )
+ 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);
@@ -751,14 +760,15 @@ int p2m_mem_paging_evict(struct domain *
/* Clear content before returning the page to Xen */
scrub_one_page(page);
- /* Put the page back so it gets freed */
- put_page(page);
-
/* Track number of paged gfns */
atomic_inc(&d->paged_pages);
ret = 0;
+ out_put:
+ /* Put the page back so it gets freed */
+ put_page(page);
+
out:
p2m_unlock(p2m);
return ret;
@@ -788,6 +798,7 @@ void p2m_mem_paging_populate(struct doma
mem_event_request_t req;
p2m_type_t p2mt;
p2m_access_t a;
+ mfn_t mfn;
struct p2m_domain *p2m = p2m_get_hostp2m(d);
/* Check that there's space on the ring for this request */
@@ -799,21 +810,26 @@ void p2m_mem_paging_populate(struct doma
/* Fix p2m mapping */
p2m_lock(p2m);
- p2m->get_entry(p2m, gfn, &p2mt, &a, p2m_query, NULL);
- if ( p2mt == p2m_ram_paged )
+ mfn = p2m->get_entry(p2m, gfn, &p2mt, &a, p2m_query, NULL);
+ /* Allow only nominated or evicted pages to enter page-in path */
+ if ( p2mt == p2m_ram_paging_out || p2mt == p2m_ram_paged )
{
- set_p2m_entry(p2m, gfn, _mfn(INVALID_MFN), 0,
- p2m_ram_paging_in_start, a);
+ /* Evict will fail now, tag this request for pager */
+ if ( p2mt == p2m_ram_paging_out )
+ req.flags |= MEM_EVENT_FLAG_EVICT_FAIL;
+
+ set_p2m_entry(p2m, gfn, mfn, 0, p2m_ram_paging_in_start, a);
audit_p2m(p2m, 1);
}
p2m_unlock(p2m);
- /* Pause domain */
- if ( v->domain->domain_id == d->domain_id )
+ /* Pause domain if request came from guest and gfn has paging type */
+ if ( p2m_is_paging(p2mt) && v->domain->domain_id == d->domain_id )
{
vcpu_pause_nosync(v);
req.flags |= MEM_EVENT_FLAG_VCPU_PAUSED;
}
+ /* No need to inform pager if the gfn is not in the page-out path */
else if ( p2mt != p2m_ram_paging_out && p2mt != p2m_ram_paged )
{
/* gfn is already on its way back and vcpu is not paused */
@@ -834,20 +850,26 @@ int p2m_mem_paging_prep(struct domain *d
struct page_info *page;
p2m_type_t p2mt;
p2m_access_t a;
+ mfn_t mfn;
struct p2m_domain *p2m = p2m_get_hostp2m(d);
int ret = -ENOMEM;
p2m_lock(p2m);
- p2m->get_entry(p2m, gfn, &p2mt, &a, p2m_query, NULL);
+ mfn = p2m->get_entry(p2m, gfn, &p2mt, &a, p2m_query, NULL);
- /* Get a free page */
- page = alloc_domheap_page(p2m->domain, 0);
- if ( unlikely(page == NULL) )
- goto out;
+ /* Allocate a page if the gfn does not have one yet */
+ if ( !mfn_valid(mfn) )
+ {
+ /* Get a free page */
+ page = alloc_domheap_page(p2m->domain, 0);
+ if ( unlikely(page == NULL) )
+ goto out;
+ mfn = page_to_mfn(page);
+ }
/* Fix p2m mapping */
- set_p2m_entry(p2m, gfn, page_to_mfn(page), 0, p2m_ram_paging_in, a);
+ set_p2m_entry(p2m, gfn, mfn, 0, p2m_ram_paging_in, a);
audit_p2m(p2m, 1);
atomic_dec(&d->paged_pages);
diff -r 4b0907c6a08c -r bdd49540f1e1 xen/include/public/mem_event.h
--- a/xen/include/public/mem_event.h
+++ b/xen/include/public/mem_event.h
@@ -38,6 +38,7 @@
/* Memory event flags */
#define MEM_EVENT_FLAG_VCPU_PAUSED (1 << 0)
#define MEM_EVENT_FLAG_DROP_PAGE (1 << 1)
+#define MEM_EVENT_FLAG_EVICT_FAIL (1 << 2)
/* Reasons for the memory event request */
#define MEM_EVENT_REASON_UNKNOWN 0 /* typical reason */
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