[PATCH 4/5] x86: don't pointlessly use get_domain_by_id()

[Jan Beulich <jbeulich@xxxxxxxx>]

For short-lived references rcu_lock_domain_by_id() is the better
(slightly cheaper) alternative.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/cpu/mcheck/mcaction.c
+++ b/xen/arch/x86/cpu/mcheck/mcaction.c
@@ -87,7 +87,7 @@ mc_memerr_dhandler(struct mca_binfo *bin
             BUG_ON( bank->mc_domid == DOMID_COW );
             if ( bank->mc_domid != DOMID_XEN )
             {
-                d = get_domain_by_id(bank->mc_domid);
+                d = rcu_lock_domain_by_id(bank->mc_domid);
                 ASSERT(d);
                 gfn = get_gpfn_from_mfn((bank->mc_addr) >> PAGE_SHIFT);
 
@@ -132,6 +132,8 @@ mc_memerr_dhandler(struct mca_binfo *bin
                     goto vmce_failed;
                 }
 
+                rcu_unlock_domain(d);
+
                 /*
                  * Impacted domain go on with domain's recovery job
                  * if the domain has its own MCA handler.
@@ -139,12 +141,11 @@ mc_memerr_dhandler(struct mca_binfo *bin
                  * its own recovery job.
                  */
                 *result = MCER_RECOVERED;
-                put_domain(d);
 
                 return;
 vmce_failed:
-                put_domain(d);
                 domain_crash(d);
+                rcu_unlock_domain(d);
             }
         }
     }
--- a/xen/arch/x86/cpu/mcheck/mce.c
+++ b/xen/arch/x86/cpu/mcheck/mce.c
@@ -1497,7 +1497,6 @@ long do_mca(XEN_GUEST_HANDLE_PARAM(xen_m
 
         if ( mc_msrinject->mcinj_flags & MC_MSRINJ_F_GPADDR )
         {
-            domid_t domid;
             struct domain *d;
             struct mcinfo_msr *msr;
             unsigned int i;
@@ -1505,17 +1504,17 @@ long do_mca(XEN_GUEST_HANDLE_PARAM(xen_m
             unsigned long gfn, mfn;
             p2m_type_t t;
 
-            domid = (mc_msrinject->mcinj_domid == DOMID_SELF) ?
-                    current->domain->domain_id : mc_msrinject->mcinj_domid;
-            if ( domid >= DOMID_FIRST_RESERVED )
-                return x86_mcerr("do_mca inject: incompatible flag "
-                                 "MC_MSRINJ_F_GPADDR with domain %d",
-                                 -EINVAL, domid);
-
-            d = get_domain_by_id(domid);
+            d = rcu_lock_domain_by_any_id(mc_msrinject->mcinj_domid);
             if ( d == NULL )
+            {
+                if ( mc_msrinject->mcinj_domid >= DOMID_FIRST_RESERVED )
+                    return x86_mcerr("do_mca inject: incompatible flag "
+                                     "MC_MSRINJ_F_GPADDR with domain %d",
+                                     -EINVAL, domid);
+
                 return x86_mcerr("do_mca inject: bad domain id %d",
                                  -EINVAL, domid);
+            }
 
             for ( i = 0, msr = &mc_msrinject->mcinj_msr[0];
                   i < mc_msrinject->mcinj_count;
@@ -1528,7 +1527,7 @@ long do_mca(XEN_GUEST_HANDLE_PARAM(xen_m
                 if ( mfn == mfn_x(INVALID_MFN) )
                 {
                     put_gfn(d, gfn);
-                    put_domain(d);
+                    rcu_unlock_domain(d);
                     return x86_mcerr("do_mca inject: bad gfn %#lx of domain 
%d",
                                      -EINVAL, gfn, domid);
                 }
@@ -1538,7 +1537,7 @@ long do_mca(XEN_GUEST_HANDLE_PARAM(xen_m
                 put_gfn(d, gfn);
             }
 
-            put_domain(d);
+            rcu_unlock_domain(d);
         }
 
         if ( !x86_mc_msrinject_verify(mc_msrinject) )
--- a/xen/arch/x86/debug.c
+++ b/xen/arch/x86/debug.c
@@ -164,13 +164,13 @@ unsigned int dbg_rw_mem(void * __user ad
                         unsigned int len, domid_t domid, bool toaddr,
                         uint64_t pgd3)
 {
-        struct domain *d = get_domain_by_id(domid);
+    struct domain *d = rcu_lock_domain_by_id(domid);
 
     if ( d )
     {
         if ( !d->is_dying )
             len = dbg_rw_guest_mem(d, addr, buf, len, toaddr, pgd3);
-        put_domain(d);
+        rcu_unlock_domain(d);
     }
 
     return len;
--- a/xen/arch/x86/irq.c
+++ b/xen/arch/x86/irq.c
@@ -323,7 +323,7 @@ void destroy_irq(unsigned int irq)
 
     if ( desc->arch.creator_domid != DOMID_INVALID )
     {
-        struct domain *d = get_domain_by_id(desc->arch.creator_domid);
+        struct domain *d = rcu_lock_domain_by_id(desc->arch.creator_domid);
 
         if ( d )
         {
@@ -334,7 +334,7 @@ void destroy_irq(unsigned int irq)
                        "Could not revoke %pd access to IRQ%u (error %d)\n",
                        d, irq, err);
 
-            put_domain(d);
+            rcu_unlock_domain(d);
         }
 
         desc->arch.creator_domid = DOMID_INVALID;