[Xen-devel] [PATCH 3/6] xen/domctl: Consolidate hypercall continuation handling at the top level

[Andrew Cooper <andrew.cooper3@citrix.com>]

More paths are going start using hypercall continuations.  We could add extra
calls to hypercall_create_continuation() but it is much easier to handle
-ERESTART once at the top level.

One complication is XEN_DOMCTL_shadow_op, which for XSA-97 and ABI
compatibility in a security fix, turn a DOMCTL continuation into
__HYPERVISOR_arch_1.  This remains as it was, gaining a comment explaining
what is going on.

With -ERESTART handling in place, the !domctl_lock_acquire() path can use the
normal exit path, instead of opencoding a subset of it locally.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wl@xen.org>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Julien Grall <julien@xen.org>
CC: Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
---
 xen/arch/x86/domctl.c           |  5 ++++-
 xen/arch/x86/mm/hap/hap.c       |  3 +--
 xen/arch/x86/mm/shadow/common.c |  3 +--
 xen/common/domctl.c             | 19 +++++--------------
 4 files changed, 11 insertions(+), 19 deletions(-)

diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index b461aadbd6..2fa0e7dda5 100644
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -326,9 +326,12 @@ long arch_do_domctl(
 
     switch ( domctl->cmd )
     {
-
     case XEN_DOMCTL_shadow_op:
         ret = paging_domctl(d, &domctl->u.shadow_op, u_domctl, 0);
+        /*
+         * Continuations from paging_domctl() switch index to arch_1, and
+         * can't use the common domctl continuation path.
+         */
         if ( ret == -ERESTART )
             return hypercall_create_continuation(__HYPERVISOR_arch_1,
                                                  "h", u_domctl);
diff --git a/xen/arch/x86/mm/hap/hap.c b/xen/arch/x86/mm/hap/hap.c
index 3d93f3451c..3996e17b7e 100644
--- a/xen/arch/x86/mm/hap/hap.c
+++ b/xen/arch/x86/mm/hap/hap.c
@@ -600,8 +600,7 @@ int hap_domctl(struct domain *d, struct xen_domctl_shadow_op *sc,
         paging_unlock(d);
         if ( preempted )
             /* Not finished.  Set up to re-run the call. */
-            rc = hypercall_create_continuation(__HYPERVISOR_domctl, "h",
-                                               u_domctl);
+            rc = -ERESTART;
         else
             /* Finished.  Return the new allocation */
             sc->mb = hap_get_allocation(d);
diff --git a/xen/arch/x86/mm/shadow/common.c b/xen/arch/x86/mm/shadow/common.c
index 6212ec2c4a..17ca21104f 100644
--- a/xen/arch/x86/mm/shadow/common.c
+++ b/xen/arch/x86/mm/shadow/common.c
@@ -3400,8 +3400,7 @@ int shadow_domctl(struct domain *d,
         paging_unlock(d);
         if ( preempted )
             /* Not finished.  Set up to re-run the call. */
-            rc = hypercall_create_continuation(
-                __HYPERVISOR_domctl, "h", u_domctl);
+            rc = -ERESTART;
         else
             /* Finished.  Return the new allocation */
             sc->mb = shadow_get_allocation(d);
diff --git a/xen/common/domctl.c b/xen/common/domctl.c
index 03d0226039..cb0295085d 100644
--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -415,10 +415,8 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
 
     if ( !domctl_lock_acquire() )
     {
-        if ( d && d != dom_io )
-            rcu_unlock_domain(d);
-        return hypercall_create_continuation(
-            __HYPERVISOR_domctl, "h", u_domctl);
+        ret = -ERESTART;
+        goto domctl_out_unlock_domonly;
     }
 
     switch ( op->cmd )
@@ -438,9 +436,6 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
         if ( guest_handle_is_null(op->u.vcpucontext.ctxt) )
         {
             ret = vcpu_reset(v);
-            if ( ret == -ERESTART )
-                ret = hypercall_create_continuation(
-                          __HYPERVISOR_domctl, "h", u_domctl);
             break;
         }
 
@@ -469,10 +464,6 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
             domain_pause(d);
             ret = arch_set_info_guest(v, c);
             domain_unpause(d);
-
-            if ( ret == -ERESTART )
-                ret = hypercall_create_continuation(
-                          __HYPERVISOR_domctl, "h", u_domctl);
         }
 
         free_vcpu_guest_context(c.nat);
@@ -585,9 +576,6 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
         domain_lock(d);
         ret = domain_kill(d);
         domain_unlock(d);
-        if ( ret == -ERESTART )
-            ret = hypercall_create_continuation(
-                __HYPERVISOR_domctl, "h", u_domctl);
         goto domctl_out_unlock_domonly;
 
     case XEN_DOMCTL_setnodeaffinity:
@@ -1080,6 +1068,9 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
     if ( copyback && __copy_to_guest(u_domctl, op, 1) )
         ret = -EFAULT;
 
+    if ( ret == -ERESTART )
+        ret = hypercall_create_continuation(__HYPERVISOR_domctl,
+                                            "h", u_domctl);
     return ret;
 }
 
-- 
2.11.0


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