[Xen-devel] [PATCH 4/6] xen/hypercall: Cope with -ERESTART on more hypercall paths

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

These hypercalls each use continue_hypercall_on_cpu(), whose API is about to
switch to use -ERESTART.  Update the soon-to-be affected paths to cope,
folding existing contination logic where applicable.

In addition:
 * For platform op and sysctl, insert a cpu_relax() into what is otherwise a
   tight spinlock loop, and make the continuation logic common at the
   epilogue.
 * Contrary to the comment in the code, kexec_exec() does return in the
   KEXEC_REBOOT case, needs to pass ret back to the caller.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Julien Grall <julien@xxxxxxx>
CC: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
---
 xen/arch/x86/platform_hypercall.c | 14 ++++++++++++--
 xen/common/compat/domain.c        |  9 ++++-----
 xen/common/domain.c               |  8 ++++----
 xen/common/kexec.c                | 20 ++++++++++++++++----
 xen/common/sysctl.c               | 13 +++++++++++--
 5 files changed, 47 insertions(+), 17 deletions(-)

diff --git a/xen/arch/x86/platform_hypercall.c 
b/xen/arch/x86/platform_hypercall.c
index b19f6ec4ed..c0c209baac 100644
--- a/xen/arch/x86/platform_hypercall.c
+++ b/xen/arch/x86/platform_hypercall.c
@@ -201,9 +201,12 @@ ret_t 
do_platform_op(XEN_GUEST_HANDLE_PARAM(xen_platform_op_t) u_xenpf_op)
      * with this vcpu.
      */
     while ( !spin_trylock(&xenpf_lock) )
+    {
+        cpu_relax();
+
         if ( hypercall_preempt_check() )
-            return hypercall_create_continuation(
-                __HYPERVISOR_platform_op, "h", u_xenpf_op);
+            goto create_continuation;
+    }
 
     switch ( op->cmd )
     {
@@ -816,6 +819,13 @@ ret_t 
do_platform_op(XEN_GUEST_HANDLE_PARAM(xen_platform_op_t) u_xenpf_op)
  out:
     spin_unlock(&xenpf_lock);
 
+    if ( ret == -ERESTART )
+    {
+    create_continuation:
+        ret = hypercall_create_continuation(__HYPERVISOR_platform_op,
+                                            "h", u_xenpf_op);
+    }
+
     return ret;
 }
 
diff --git a/xen/common/compat/domain.c b/xen/common/compat/domain.c
index 11c6afc463..1a14403672 100644
--- a/xen/common/compat/domain.c
+++ b/xen/common/compat/domain.c
@@ -79,11 +79,6 @@ int compat_vcpu_op(int cmd, unsigned int vcpuid, 
XEN_GUEST_HANDLE_PARAM(void) ar
 
             xfree(ctxt);
         }
-
-        if ( rc == -ERESTART )
-            rc = hypercall_create_continuation(__HYPERVISOR_vcpu_op, "iih",
-                                               cmd, vcpuid, arg);
-
         break;
     }
 
@@ -130,6 +125,10 @@ int compat_vcpu_op(int cmd, unsigned int vcpuid, 
XEN_GUEST_HANDLE_PARAM(void) ar
         break;
     }
 
+    if ( rc == -ERESTART )
+        rc = hypercall_create_continuation(__HYPERVISOR_vcpu_op, "iih",
+                                           cmd, vcpuid, arg);
+
     return rc;
 }
 
diff --git a/xen/common/domain.c b/xen/common/domain.c
index 865a1cb9d7..ab7e4d09c0 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -1422,10 +1422,6 @@ long do_vcpu_op(int cmd, unsigned int vcpuid, 
XEN_GUEST_HANDLE_PARAM(void) arg)
             return -EINVAL;
 
         rc = arch_initialise_vcpu(v, arg);
-        if ( rc == -ERESTART )
-            rc = hypercall_create_continuation(__HYPERVISOR_vcpu_op, "iih",
-                                               cmd, vcpuid, arg);
-
         break;
 
     case VCPUOP_up:
@@ -1598,6 +1594,10 @@ long do_vcpu_op(int cmd, unsigned int vcpuid, 
XEN_GUEST_HANDLE_PARAM(void) arg)
         break;
     }
 
+    if ( rc == -ERESTART )
+        rc = hypercall_create_continuation(__HYPERVISOR_vcpu_op, "iih",
+                                           cmd, vcpuid, arg);
+
     return rc;
 }
 
diff --git a/xen/common/kexec.c b/xen/common/kexec.c
index a262cc5a18..2fca75cec0 100644
--- a/xen/common/kexec.c
+++ b/xen/common/kexec.c
@@ -842,7 +842,7 @@ static int kexec_exec(XEN_GUEST_HANDLE_PARAM(void) uarg)
         break;
     }
 
-    return -EINVAL; /* never reached */
+    return ret;
 }
 
 static int kexec_swap_images(int type, struct kexec_image *new,
@@ -1220,7 +1220,7 @@ static int do_kexec_op_internal(unsigned long op,
         return ret;
 
     if ( test_and_set_bit(KEXEC_FLAG_IN_HYPERCALL, &kexec_flags) )
-        return hypercall_create_continuation(__HYPERVISOR_kexec_op, "lh", op, 
uarg);
+        return -ERESTART;
 
     switch ( op )
     {
@@ -1263,13 +1263,25 @@ static int do_kexec_op_internal(unsigned long op,
 
 long do_kexec_op(unsigned long op, XEN_GUEST_HANDLE_PARAM(void) uarg)
 {
-    return do_kexec_op_internal(op, uarg, 0);
+    int ret = do_kexec_op_internal(op, uarg, 0);
+
+    if ( ret == -ERESTART )
+        ret = hypercall_create_continuation(__HYPERVISOR_kexec_op,
+                                            "lh", op, uarg);
+
+    return ret;
 }
 
 #ifdef CONFIG_COMPAT
 int compat_kexec_op(unsigned long op, XEN_GUEST_HANDLE_PARAM(void) uarg)
 {
-    return do_kexec_op_internal(op, uarg, 1);
+    int ret = do_kexec_op_internal(op, uarg, 1);
+
+    if ( ret == -ERESTART )
+        ret = hypercall_create_continuation(__HYPERVISOR_kexec_op,
+                                            "lh", op, uarg);
+
+    return ret;
 }
 #endif
 
diff --git a/xen/common/sysctl.c b/xen/common/sysctl.c
index f88a285e7f..7b55047bb9 100644
--- a/xen/common/sysctl.c
+++ b/xen/common/sysctl.c
@@ -51,9 +51,12 @@ long do_sysctl(XEN_GUEST_HANDLE_PARAM(xen_sysctl_t) u_sysctl)
      * with this vcpu.
      */
     while ( !spin_trylock(&sysctl_lock) )
+    {
+        cpu_relax();
+
         if ( hypercall_preempt_check() )
-            return hypercall_create_continuation(
-                __HYPERVISOR_sysctl, "h", u_sysctl);
+            goto create_continuation;
+    }
 
     switch ( op->cmd )
     {
@@ -516,6 +519,12 @@ long do_sysctl(XEN_GUEST_HANDLE_PARAM(xen_sysctl_t) 
u_sysctl)
          __copy_to_guest(u_sysctl, op, 1) )
         ret = -EFAULT;
 
+    if ( ret == -ERESTART )
+    {
+    create_continuation:
+        ret = hypercall_create_continuation(__HYPERVISOR_sysctl, "h", 
u_sysctl);
+    }
+
     return ret;
 }
 
-- 
2.11.0


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