KVM: x86 emulator: check io permissions only once for string pio

Do not recheck io permission on every iteration.

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

3 files changed, 8 insertions, 0 deletions

diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
index 0f901c16cf1c..8762411fe9bb 100644
--- a/arch/x86/include/asm/kvm_emulate.h
+++ b/arch/x86/include/asm/kvm_emulate.h
@@ -224,6 +224,7 @@ struct x86_emulate_ctxt {
         int interruptibility;
 
         bool restart; /* restart string instruction after writeback */
+        bool perm_ok; /* do not check permissions if true */
 
         int exception; /* exception that happens during emulation or -1 */
         u32 error_code; /* error code for exception */
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 4d49514a919e..760e2b030e68 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1621,9 +1621,15 @@ static bool emulator_io_permited(struct x86_emulate_ctxt *ctxt,
                                  struct x86_emulate_ops *ops,
                                  u16 port, u16 len)
 {
+        if (ctxt->perm_ok)
+                return true;
+
         if (emulator_bad_iopl(ctxt, ops))
                 if (!emulator_io_port_access_allowed(ctxt, ops, port, len))
                         return false;
+
+        ctxt->perm_ok = true;
+
         return true;
 }
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3cbe8032394a..35c0f4e4a621 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3997,6 +3997,7 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
                 memcpy(c->regs, vcpu->arch.regs, sizeof c->regs);
                 vcpu->arch.emulate_ctxt.interruptibility = 0;
                 vcpu->arch.emulate_ctxt.exception = -1;
+                vcpu->arch.emulate_ctxt.perm_ok = false;
 
                 r = x86_decode_insn(&vcpu->arch.emulate_ctxt);
                 trace_kvm_emulate_insn_start(vcpu);