KVM: Call x86_decode_insn() only when needed

Move emulate_ctxt to kvm_vcpu to keep emulate context when we exit from kvm
module. Call x86_decode_insn() only when needed. Modify x86_emulate_insn() to
not modify the context if it must be re-entered.

Signed-off-by: Laurent Vivier <Laurent.Vivier@bull.net>
Signed-off-by: Avi Kivity <avi@qumranet.com>

5 files changed, 82 insertions, 45 deletions

diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
index da9c3aa1c08c..e885b190b798 100644
--- a/drivers/kvm/kvm.h
+++ b/drivers/kvm/kvm.h
@@ -207,6 +207,8 @@ enum {
         VCPU_SREG_LDTR,
 };
 
+#include "x86_emulate.h"
+
 struct kvm_pio_request {
         unsigned long count;
         int cur_count;
@@ -380,6 +382,10 @@ struct kvm_vcpu {
 
         int cpuid_nent;
         struct kvm_cpuid_entry cpuid_entries[KVM_MAX_CPUID_ENTRIES];
+
+        /* emulate context */
+
+        struct x86_emulate_ctxt emulate_ctxt;
 };
 
 struct kvm_mem_alias {
@@ -555,7 +561,7 @@ enum emulation_result {
 };
 
 int emulate_instruction(struct kvm_vcpu *vcpu, struct kvm_run *run,
-                        unsigned long cr2, u16 error_code);
+                        unsigned long cr2, u16 error_code, int no_decode);
 void kvm_report_emulation_failure(struct kvm_vcpu *cvpu, const char *context);
 void realmode_lgdt(struct kvm_vcpu *vcpu, u16 size, unsigned long address);
 void realmode_lidt(struct kvm_vcpu *vcpu, u16 size, unsigned long address);
diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index 800ab5028ed3..710483669f34 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -1251,45 +1251,56 @@ struct x86_emulate_ops emulate_ops = {
 int emulate_instruction(struct kvm_vcpu *vcpu,
                         struct kvm_run *run,
                         unsigned long cr2,
-                        u16 error_code)
+                        u16 error_code,
+                        int no_decode)
 {
-        struct x86_emulate_ctxt emulate_ctxt;
-        int r;
-        int cs_db, cs_l;
+        int r = 0;
 
         vcpu->mmio_fault_cr2 = cr2;
         kvm_x86_ops->cache_regs(vcpu);
 
-        kvm_x86_ops->get_cs_db_l_bits(vcpu, &cs_db, &cs_l);
-
-        emulate_ctxt.vcpu = vcpu;
-        emulate_ctxt.eflags = kvm_x86_ops->get_rflags(vcpu);
-        emulate_ctxt.cr2 = cr2;
-        emulate_ctxt.mode = (emulate_ctxt.eflags & X86_EFLAGS_VM)
-                ? X86EMUL_MODE_REAL : cs_l
-                ? X86EMUL_MODE_PROT64 : cs_db
-                ? X86EMUL_MODE_PROT32 : X86EMUL_MODE_PROT16;
-
-        if (emulate_ctxt.mode == X86EMUL_MODE_PROT64) {
-                emulate_ctxt.cs_base = 0;
-                emulate_ctxt.ds_base = 0;
-                emulate_ctxt.es_base = 0;
-                emulate_ctxt.ss_base = 0;
-        } else {
-                emulate_ctxt.cs_base = get_segment_base(vcpu, VCPU_SREG_CS);
-                emulate_ctxt.ds_base = get_segment_base(vcpu, VCPU_SREG_DS);
-                emulate_ctxt.es_base = get_segment_base(vcpu, VCPU_SREG_ES);
-                emulate_ctxt.ss_base = get_segment_base(vcpu, VCPU_SREG_SS);
-        }
-
-        emulate_ctxt.gs_base = get_segment_base(vcpu, VCPU_SREG_GS);
-        emulate_ctxt.fs_base = get_segment_base(vcpu, VCPU_SREG_FS);
-
         vcpu->mmio_is_write = 0;
         vcpu->pio.string = 0;
-        r = x86_decode_insn(&emulate_ctxt, &emulate_ops);
+
+        if (!no_decode) {
+                int cs_db, cs_l;
+                kvm_x86_ops->get_cs_db_l_bits(vcpu, &cs_db, &cs_l);
+
+                vcpu->emulate_ctxt.vcpu = vcpu;
+                vcpu->emulate_ctxt.eflags = kvm_x86_ops->get_rflags(vcpu);
+                vcpu->emulate_ctxt.cr2 = cr2;
+                vcpu->emulate_ctxt.mode =
+                        (vcpu->emulate_ctxt.eflags & X86_EFLAGS_VM)
+                        ? X86EMUL_MODE_REAL : cs_l
+                        ? X86EMUL_MODE_PROT64 : cs_db
+                        ? X86EMUL_MODE_PROT32 : X86EMUL_MODE_PROT16;
+
+                if (vcpu->emulate_ctxt.mode == X86EMUL_MODE_PROT64) {
+                        vcpu->emulate_ctxt.cs_base = 0;
+                        vcpu->emulate_ctxt.ds_base = 0;
+                        vcpu->emulate_ctxt.es_base = 0;
+                        vcpu->emulate_ctxt.ss_base = 0;
+                } else {
+                        vcpu->emulate_ctxt.cs_base =
+                                        get_segment_base(vcpu, VCPU_SREG_CS);
+                        vcpu->emulate_ctxt.ds_base =
+                                        get_segment_base(vcpu, VCPU_SREG_DS);
+                        vcpu->emulate_ctxt.es_base =
+                                        get_segment_base(vcpu, VCPU_SREG_ES);
+                        vcpu->emulate_ctxt.ss_base =
+                                        get_segment_base(vcpu, VCPU_SREG_SS);
+                }
+
+                vcpu->emulate_ctxt.gs_base =
+                                        get_segment_base(vcpu, VCPU_SREG_GS);
+                vcpu->emulate_ctxt.fs_base =
+                                        get_segment_base(vcpu, VCPU_SREG_FS);
+
+                r = x86_decode_insn(&vcpu->emulate_ctxt, &emulate_ops);
+        }
+
         if (r == 0)
-                r = x86_emulate_insn(&emulate_ctxt, &emulate_ops);
+                r = x86_emulate_insn(&vcpu->emulate_ctxt, &emulate_ops);
 
         if (vcpu->pio.string)
                 return EMULATE_DO_MMIO;
@@ -1313,7 +1324,7 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
         }
 
         kvm_x86_ops->decache_regs(vcpu);
-        kvm_x86_ops->set_rflags(vcpu, emulate_ctxt.eflags);
+        kvm_x86_ops->set_rflags(vcpu, vcpu->emulate_ctxt.eflags);
 
         if (vcpu->mmio_is_write) {
                 vcpu->mmio_needed = 0;
@@ -2055,7 +2066,7 @@ static int kvm_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
                 vcpu->mmio_read_completed = 1;
                 vcpu->mmio_needed = 0;
                 r = emulate_instruction(vcpu, kvm_run,
-                                        vcpu->mmio_fault_cr2, 0);
+                                        vcpu->mmio_fault_cr2, 0, 1);
                 if (r == EMULATE_DO_MMIO) {
                         /*
                          * Read-modify-write.  Back to userspace.
diff --git a/drivers/kvm/svm.c b/drivers/kvm/svm.c
index 794d95416f7b..f268bd51f337 100644
--- a/drivers/kvm/svm.c
+++ b/drivers/kvm/svm.c
@@ -960,7 +960,7 @@ static int pf_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
                 return 1;
         }
         er = emulate_instruction(&svm->vcpu, kvm_run, fault_address,
-                                 error_code);
+                                 error_code, 0);
         mutex_unlock(&kvm->lock);
 
         switch (er) {
@@ -984,7 +984,7 @@ static int ud_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
 {
         int er;
 
-        er = emulate_instruction(&svm->vcpu, kvm_run, 0, 0);
+        er = emulate_instruction(&svm->vcpu, kvm_run, 0, 0, 0);
         if (er != EMULATE_DONE)
                 inject_ud(&svm->vcpu);
 
@@ -1027,7 +1027,8 @@ static int io_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
         string = (io_info & SVM_IOIO_STR_MASK) != 0;
 
         if (string) {
-                if (emulate_instruction(&svm->vcpu, kvm_run, 0, 0) == EMULATE_DO_MMIO)
+                if (emulate_instruction(&svm->vcpu,
+                                        kvm_run, 0, 0, 0) == EMULATE_DO_MMIO)
                         return 0;
                 return 1;
         }
@@ -1086,7 +1087,7 @@ static int cpuid_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
 static int emulate_on_interception(struct vcpu_svm *svm,
                                    struct kvm_run *kvm_run)
 {
-        if (emulate_instruction(&svm->vcpu, NULL, 0, 0) != EMULATE_DONE)
+        if (emulate_instruction(&svm->vcpu, NULL, 0, 0, 0) != EMULATE_DONE)
                 pr_unimpl(&svm->vcpu, "%s: failed\n", __FUNCTION__);
         return 1;
 }
diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
index 47c827d3007c..91768d5dbfb9 100644
--- a/drivers/kvm/vmx.c
+++ b/drivers/kvm/vmx.c
@@ -1750,7 +1750,7 @@ static int handle_rmode_exception(struct kvm_vcpu *vcpu,
          * Cause the #SS fault with 0 error code in VM86 mode.
          */
         if (((vec == GP_VECTOR) || (vec == SS_VECTOR)) && err_code == 0)
-                if (emulate_instruction(vcpu, NULL, 0, 0) == EMULATE_DONE)
+                if (emulate_instruction(vcpu, NULL, 0, 0, 0) == EMULATE_DONE)
                         return 1;
         return 0;
 }
@@ -1787,7 +1787,7 @@ static int handle_exception(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
         }
 
         if (is_invalid_opcode(intr_info)) {
-                er = emulate_instruction(vcpu, kvm_run, 0, 0);
+                er = emulate_instruction(vcpu, kvm_run, 0, 0, 0);
                 if (er != EMULATE_DONE)
                         vmx_inject_ud(vcpu);
 
@@ -1812,7 +1812,7 @@ static int handle_exception(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
                         return 1;
                 }
 
-                er = emulate_instruction(vcpu, kvm_run, cr2, error_code);
+                er = emulate_instruction(vcpu, kvm_run, cr2, error_code, 0);
                 mutex_unlock(&vcpu->kvm->lock);
 
                 switch (er) {
@@ -1873,7 +1873,8 @@ static int handle_io(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
         string = (exit_qualification & 16) != 0;
 
         if (string) {
-                if (emulate_instruction(vcpu, kvm_run, 0, 0) == EMULATE_DO_MMIO)
+                if (emulate_instruction(vcpu,
+                                        kvm_run, 0, 0, 0) == EMULATE_DO_MMIO)
                         return 0;
                 return 1;
         }
diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
index c191093982d8..dc9d2a870fbc 100644
--- a/drivers/kvm/x86_emulate.c
+++ b/drivers/kvm/x86_emulate.c
@@ -913,10 +913,19 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
         unsigned long cr2 = ctxt->cr2;
         int no_wb = 0;
         u64 msr_data;
+        unsigned long saved_eip = 0;
         unsigned long _eflags = ctxt->eflags;
         struct decode_cache *c = &ctxt->decode;
         int rc = 0;
 
+        /* Shadow copy of register state. Committed on successful emulation.
+         * NOTE: we can copy them from vcpu as x86_decode_insn() doesn't
+         * modify them.
+         */
+
+        memcpy(c->regs, ctxt->vcpu->regs, sizeof c->regs);
+        saved_eip = c->eip;
+
         if ((c->d & ModRM) && (c->modrm_mod != 3))
                 cr2 = c->modrm_ea;
 
@@ -1250,7 +1259,11 @@ writeback:
         ctxt->vcpu->rip = c->eip;
 
 done:
-        return (rc == X86EMUL_UNHANDLEABLE) ? -1 : 0;
+        if (rc == X86EMUL_UNHANDLEABLE) {
+                c->eip = saved_eip;
+                return -1;
+        }
+        return 0;
 
 special_insn:
         if (c->twobyte)
@@ -1305,8 +1318,10 @@ push:
                                 register_address(ctxt->es_base,
                                                  c->regs[VCPU_REGS_RDI]),
                                 c->rep_prefix,
-                                c->regs[VCPU_REGS_RDX]) == 0)
+                                c->regs[VCPU_REGS_RDX]) == 0) {
+                        c->eip = saved_eip;
                         return -1;
+                }
                 return 0;
         case 0x6e:              /* outsb */
         case 0x6f:              /* outsw/outsd */
@@ -1321,8 +1336,10 @@ push:
                                                         ctxt->ds_base,
                                                  c->regs[VCPU_REGS_RSI]),
                                 c->rep_prefix,
-                                c->regs[VCPU_REGS_RDX]) == 0)
+                                c->regs[VCPU_REGS_RDX]) == 0) {
+                        c->eip = saved_eip;
                         return -1;
+                }
                 return 0;
         case 0x70 ... 0x7f: /* jcc (short) */ {
                 int rel = insn_fetch(s8, 1, c->eip);
@@ -1711,5 +1728,6 @@ twobyte_special_insn:
 
 cannot_emulate:
         DPRINTF("Cannot emulate %02x\n", c->b);
+        c->eip = saved_eip;
         return -1;
 }