x86 shadow: Reduce scope of shadow lock.

emulate_map_dest doesn't require holding lock, since
only shadow related operation possibly involved is to
remove shadow which is less frequent and can acquire
lock inside. Rest are either guest table walk or
per-vcpu monitor table manipulation

Signed-off-by Kevin Tian <kevin.tian@intel.com>

diff --git a/xen/arch/x86/mm/shadow/multi.c b/xen/arch/x86/mm/shadow/multi.c
index 1be74c70d639ddd683631898fa50ba42a7d6837a..8407beacf753424c97a676a524a20500094b70e6 100644 (file)
--- a/xen/arch/x86/mm/shadow/multi.c
+++ b/xen/arch/x86/mm/shadow/multi.c
@@ -4216,15 +4216,12 @@ sh_x86_emulate_write(struct vcpu *v, unsigned long vaddr, void *src,
     if ( (vaddr & (bytes - 1)) && !is_hvm_vcpu(v)  )
         return X86EMUL_UNHANDLEABLE;
 
-    shadow_lock(v->domain);
     addr = emulate_map_dest(v, vaddr, bytes, sh_ctxt);
     if ( emulate_map_dest_failed(addr) )
-    {
-        shadow_unlock(v->domain);
         return ((addr == MAPPING_EXCEPTION) ?
                 X86EMUL_EXCEPTION : X86EMUL_UNHANDLEABLE);
-    }
 
+    shadow_lock(v->domain);
     memcpy(addr, src, bytes);
 
     emulate_unmap_dest(v, addr, bytes, sh_ctxt);
@@ -4246,16 +4243,12 @@ sh_x86_emulate_cmpxchg(struct vcpu *v, unsigned long vaddr,
     if ( (vaddr & (bytes - 1)) && !is_hvm_vcpu(v)  )
         return X86EMUL_UNHANDLEABLE;
 
-    shadow_lock(v->domain);
-
     addr = emulate_map_dest(v, vaddr, bytes, sh_ctxt);
     if ( emulate_map_dest_failed(addr) )
-    {
-        shadow_unlock(v->domain);
         return ((addr == MAPPING_EXCEPTION) ?
                 X86EMUL_EXCEPTION : X86EMUL_UNHANDLEABLE);
-    }
 
+    shadow_lock(v->domain);
     switch ( bytes )
     {
     case 1: prev = cmpxchg(((u8 *)addr), old, new);  break;
@@ -4294,18 +4287,15 @@ sh_x86_emulate_cmpxchg8b(struct vcpu *v, unsigned long vaddr,
     if ( (vaddr & 7) && !is_hvm_vcpu(v) )
         return X86EMUL_UNHANDLEABLE;
 
-    shadow_lock(v->domain);
-
     addr = emulate_map_dest(v, vaddr, 8, sh_ctxt);
     if ( emulate_map_dest_failed(addr) )
-    {
-        shadow_unlock(v->domain);
         return ((addr == MAPPING_EXCEPTION) ?
                 X86EMUL_EXCEPTION : X86EMUL_UNHANDLEABLE);
-    }
 
     old = (((u64) old_hi) << 32) | (u64) old_lo;
     new = (((u64) new_hi) << 32) | (u64) new_lo;
+
+    shadow_lock(v->domain);
     prev = cmpxchg(((u64 *)addr), old, new);
 
     if ( prev != old )