[PATCH 2/2] KVM: x86 emulator: check io permissions only once for string pio

Gleb Natapov
2010-07-29T12:11:54Z

Do not recheck io permission on every iteration.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
---
arch/x86/include/asm/kvm_emulate.h | 1 +
arch/x86/kvm/emulate.c | 6 ++++++
arch/x86/kvm/x86.c | 1 +
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 51cfd73..ded05cf 100644
--- a/arch/x86/include/asm/kvm_emulate.h
+++ b/arch/x86/include/asm/kvm_emulate.h
@@ -216,6 +216,7 @@ 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 b38bd8b..3996fb0 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2161,9 +2161,15 @@ 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 7e5f075..de54582 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, &emulate_ops);
trace_kvm_emulate_insn_start(vcpu);
--
1.7.1