From: Tamas K Lengyel <tamas.lengyel@intel.com>
To: xen-devel@lists.xenproject.org
Cc: "Tamas K Lengyel" <tamas@tklengyel.com>,
"Tamas K Lengyel" <tamas.lengyel@intel.com>,
"Wei Liu" <wl@xen.org>,
"Andrew Cooper" <andrew.cooper3@citrix.com>,
"Ian Jackson" <ian.jackson@eu.citrix.com>,
"George Dunlap" <george.dunlap@citrix.com>,
"Stefano Stabellini" <sstabellini@kernel.org>,
"Jan Beulich" <jbeulich@suse.com>,
"Julien Grall" <julien@xen.org>,
"Roger Pau Monné" <roger.pau@citrix.com>
Subject: [Xen-devel] [PATCH v12 2/3] x86/mem_sharing: reset a fork
Date: Mon, 23 Mar 2020 10:04:36 -0700 [thread overview]
Message-ID: <46457bd6e877abe12a8c005c23f0f1aab13afd24.1584981438.git.tamas.lengyel@intel.com> (raw)
In-Reply-To: <cover.1584981438.git.tamas.lengyel@intel.com>
Implement hypercall that allows a fork to shed all memory that got allocated
for it during its execution and re-load its vCPU context from the parent VM.
This allows the forked VM to reset into the same state the parent VM is in a
faster way then creating a new fork would be. Measurements show about a 2x
speedup during normal fuzzing operations. Performance may vary depending how
much memory got allocated for the forked VM. If it has been completely
deduplicated from the parent VM then creating a new fork would likely be more
performant.
Signed-off-by: Tamas K Lengyel <tamas.lengyel@intel.com>
---
v12: remove continuation & add comment back
address style issues pointed out by Jan
---
xen/arch/x86/mm/mem_sharing.c | 77 +++++++++++++++++++++++++++++++++++
xen/include/public/memory.h | 1 +
2 files changed, 78 insertions(+)
diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
index 23deeddff2..930a5f58ef 100644
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -1775,6 +1775,60 @@ static int fork(struct domain *cd, struct domain *d)
return rc;
}
+/*
+ * The fork reset operation is intended to be used on short-lived forks only.
+ * There is no hypercall continuation operation implemented for this reason.
+ * For forks that obtain a larger memory footprint it is likely going to be
+ * more performant to create a new fork instead of resetting an existing one.
+ *
+ * TODO: In case this hypercall would become useful on forks with larger memory
+ * footprints the hypercall continuation should be implemented (or if this
+ * feature needs to be become "stable").
+ */
+static int mem_sharing_fork_reset(struct domain *d, struct domain *pd)
+{
+ int rc;
+ struct p2m_domain *p2m = p2m_get_hostp2m(d);
+ struct page_info *page, *tmp;
+
+ spin_lock(&d->page_alloc_lock);
+ domain_pause(d);
+
+ page_list_for_each_safe(page, tmp, &d->page_list)
+ {
+ p2m_type_t p2mt;
+ p2m_access_t p2ma;
+ mfn_t mfn = page_to_mfn(page);
+ gfn_t gfn = mfn_to_gfn(d, mfn);
+
+ mfn = __get_gfn_type_access(p2m, gfn_x(gfn), &p2mt, &p2ma,
+ 0, NULL, false);
+
+ /* only reset pages that are sharable */
+ if ( !p2m_is_sharable(p2mt) )
+ continue;
+
+ /* take an extra reference or just skip if can't for whatever reason */
+ if ( !get_page(page, d) )
+ continue;
+
+ /* forked memory is 4k, not splitting large pages so this must work */
+ rc = p2m->set_entry(p2m, gfn, INVALID_MFN, PAGE_ORDER_4K,
+ p2m_invalid, p2m_access_rwx, -1);
+ ASSERT(!rc);
+
+ put_page_alloc_ref(page);
+ put_page(page);
+ }
+
+ rc = copy_settings(d, pd);
+
+ domain_unpause(d);
+ spin_unlock(&d->page_alloc_lock);
+
+ return rc;
+}
+
int mem_sharing_memop(XEN_GUEST_HANDLE_PARAM(xen_mem_sharing_op_t) arg)
{
int rc;
@@ -2066,6 +2120,29 @@ int mem_sharing_memop(XEN_GUEST_HANDLE_PARAM(xen_mem_sharing_op_t) arg)
break;
}
+ case XENMEM_sharing_op_fork_reset:
+ {
+ struct domain *pd;
+
+ rc = -EINVAL;
+ if ( mso.u.fork.pad[0] || mso.u.fork.pad[1] ||
+ mso.u.fork.pad[2] )
+ goto out;
+
+ rc = -ENOSYS;
+ if ( !d->parent )
+ goto out;
+
+ rc = rcu_lock_live_remote_domain_by_id(d->parent->domain_id, &pd);
+ if ( rc )
+ goto out;
+
+ rc = mem_sharing_fork_reset(d, pd);
+
+ rcu_unlock_domain(pd);
+ break;
+ }
+
default:
rc = -ENOSYS;
break;
diff --git a/xen/include/public/memory.h b/xen/include/public/memory.h
index 5ee4e0da12..d36d64b8dc 100644
--- a/xen/include/public/memory.h
+++ b/xen/include/public/memory.h
@@ -483,6 +483,7 @@ DEFINE_XEN_GUEST_HANDLE(xen_mem_access_op_t);
#define XENMEM_sharing_op_audit 7
#define XENMEM_sharing_op_range_share 8
#define XENMEM_sharing_op_fork 9
+#define XENMEM_sharing_op_fork_reset 10
#define XENMEM_SHARING_OP_S_HANDLE_INVALID (-10)
#define XENMEM_SHARING_OP_C_HANDLE_INVALID (-9)
--
2.20.1
next prev parent reply other threads:[~2020-03-23 17:05 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-23 17:04 [Xen-devel] [PATCH v12 0/3] VM forking Tamas K Lengyel
2020-03-23 17:04 ` [Xen-devel] [PATCH v12 1/3] xen/mem_sharing: " Tamas K Lengyel
2020-03-25 15:47 ` Roger Pau Monné
2020-03-25 16:04 ` Tamas K Lengyel
2020-03-25 16:16 ` Tamas K Lengyel
2020-03-25 16:34 ` Tamas K Lengyel
2020-03-25 16:42 ` Julien Grall
2020-03-25 16:47 ` Tamas K Lengyel
2020-03-25 16:51 ` Julien Grall
2020-03-25 17:00 ` Tamas K Lengyel
2020-03-25 17:16 ` Roger Pau Monné
2020-03-25 17:47 ` Tamas K Lengyel
2020-03-25 16:54 ` Roger Pau Monné
2020-03-26 7:02 ` Jan Beulich
2020-03-26 8:42 ` Roger Pau Monné
2020-03-26 7:07 ` Jan Beulich
2020-03-26 9:10 ` Roger Pau Monné
2020-03-26 17:01 ` Tamas K Lengyel
2020-03-26 12:33 ` Jan Beulich
2020-03-26 14:52 ` Tamas K Lengyel
2020-03-23 17:04 ` Tamas K Lengyel [this message]
2020-03-25 15:52 ` [Xen-devel] [PATCH v12 2/3] x86/mem_sharing: reset a fork Roger Pau Monné
2020-03-25 15:54 ` Tamas K Lengyel
2020-03-26 10:16 ` Jan Beulich
2020-03-26 14:48 ` Tamas K Lengyel
2020-03-26 14:52 ` Jan Beulich
2020-03-26 14:53 ` Tamas K Lengyel
2020-03-26 23:40 ` Tamas K Lengyel
2020-03-23 17:04 ` [Xen-devel] [PATCH v12 3/3] xen/tools: VM forking toolstack side Tamas K Lengyel
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