KVM: x86 emulator: drop unneeded call to get_segment()

setup_syscalls_segments() calls get_segment() and than overwrites all
but one of the structure fields and this one should also be overwritten
anyway, so we can drop call to get_segment() and avoid a couple of vmreads
on vmx. Also drop zeroing ss/cs structures since most of the fields are
set anyway. Just set those that were not set explicitly.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 2c5d1e6..10f0136 100644 (file)
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2035,12 +2035,6 @@ static void
 setup_syscalls_segments(struct x86_emulate_ctxt *ctxt,
                        struct desc_struct *cs, struct desc_struct *ss)
 {
-       u16 selector;
-
-       memset(cs, 0, sizeof(struct desc_struct));
-       ctxt->ops->get_segment(ctxt, &selector, cs, NULL, VCPU_SREG_CS);
-       memset(ss, 0, sizeof(struct desc_struct));
-
        cs->l = 0;              /* will be adjusted later */
        set_desc_base(cs, 0);   /* flat segment */
        cs->g = 1;              /* 4kb granularity */
@@ -2050,6 +2044,7 @@ setup_syscalls_segments(struct x86_emulate_ctxt *ctxt,
        cs->dpl = 0;            /* will be adjusted later */
        cs->p = 1;
        cs->d = 1;
+       cs->avl = 0;
 
        set_desc_base(ss, 0);   /* flat segment */
        set_desc_limit(ss, 0xfffff);    /* 4GB limit */
@@ -2059,6 +2054,8 @@ setup_syscalls_segments(struct x86_emulate_ctxt *ctxt,
        ss->d = 1;              /* 32bit stack segment */
        ss->dpl = 0;
        ss->p = 1;
+       ss->l = 0;
+       ss->avl = 0;
 }
 
 static bool vendor_intel(struct x86_emulate_ctxt *ctxt)