On 08/01/2020 17:14, Tamas K Lengyel wrote:
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.leng...@intel.com>
---
xen/arch/x86/mm/mem_sharing.c | 79 +++++++++++++++++++++++++++++++++++
xen/include/public/memory.h | 1 +
2 files changed, 80 insertions(+)
diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
index d544801681..aaa678da14 100644
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -1607,6 +1607,62 @@ static int mem_sharing_fork(struct domain *d, struct
domain *cd)
return 0;
}
+/*
+ * 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.
+ */
+static int mem_sharing_fork_reset(struct domain *d, struct domain *cd)
+{
+ int rc;
+ struct p2m_domain* p2m = p2m_get_hostp2m(cd);
+ struct page_info *page, *tmp;
+
+ if ( !d->controller_pause_count &&
+ (rc = domain_pause_by_systemcontroller(d)) )
+ return rc;
Similar question as patch #15 here.
+
+ page_list_for_each_safe(page, tmp, &cd->page_list)
+ {
+ p2m_type_t p2mt;
+ p2m_access_t p2ma;
+ gfn_t gfn;
+ mfn_t mfn = page_to_mfn(page);
+
+ if ( !mfn_valid(mfn) )
+ continue;
+
+ gfn = mfn_to_gfn(cd, mfn);
+ mfn = __get_gfn_type_access(p2m, gfn_x(gfn), &p2mt, &p2ma,
+ 0, NULL, false);
+
+ if ( !p2m_is_ram(p2mt) || p2m_is_shared(p2mt) )
+ continue;
+
+ /* take an extra reference */
+ if ( !get_page(page, cd) )
+ continue;
+
+ 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);
+ }
+
+ if ( (rc = hvm_copy_context_and_params(d, cd)) )
+ return rc;
+
+ fork_tsc(d, cd);
+
+ return 0;
+}
+
int mem_sharing_memop(XEN_GUEST_HANDLE_PARAM(xen_mem_sharing_op_t) arg)
{
int rc;
@@ -1909,6 +1965,29 @@ 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(pd, d);
+
+ rcu_unlock_domain(pd);
+ break;
+ }
+
default:
rc = -ENOSYS;
break;
diff --git a/xen/include/public/memory.h b/xen/include/public/memory.h
index 90a3f4498e..e3d063e22e 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)
--
Julien Grall
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