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KVM: x86 emulator: restart string instruction without going back to a guest. 

Currently when string instruction is only partially complete we go back
to a guest mode, guest tries to reexecute instruction and exits again
and at this point emulation continues. Avoid all of this by restarting
instruction without going back to a guest mode, but return to a guest
mode each 1024 iterations to allow interrupt injection. Pending
exception causes immediate guest entry too.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Gleb Natapov 2010-03-18 15:20:26 +02:00 committed by Avi Kivity
parent cb404fe089
commit 5cd21917da
3 changed files with 42 additions and 12 deletions
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1
arch/x86/include/asm/kvm_emulate.h
View File

@ -193,6 +193,7 @@ struct x86_emulate_ctxt {
/* interruptibility state, as a result of execution of STI or MOV SS */
int interruptibility;
bool restart; /* restart string instruction after writeback */
/* decode cache */
struct decode_cache decode;
};

34
arch/x86/kvm/emulate.c
View File

@ -927,8 +927,11 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
int mode = ctxt->mode;
int def_op_bytes, def_ad_bytes, group;
/* Shadow copy of register state. Committed on successful emulation. */
/* we cannot decode insn before we complete previous rep insn */
WARN_ON(ctxt->restart);
/* Shadow copy of register state. Committed on successful emulation. */
memset(c, 0, sizeof(struct decode_cache));
c->eip = ctxt->eip;
ctxt->cs_base = seg_base(ctxt, VCPU_SREG_CS);
@ -2426,6 +2429,7 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
u64 msr_data;
struct decode_cache *c = &ctxt->decode;
int rc = X86EMUL_CONTINUE;
int saved_dst_type = c->dst.type;
ctxt->interruptibility = 0;
@ -2454,8 +2458,11 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
}
if (c->rep_prefix && (c->d & String)) {
ctxt->restart = true;
/* All REP prefixes have the same first termination condition */
if (address_mask(c, c->regs[VCPU_REGS_RCX]) == 0) {
string_done:
ctxt->restart = false;
kvm_rip_write(ctxt->vcpu, c->eip);
goto done;
}
@ -2467,17 +2474,13 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
* - if REPNE/REPNZ and ZF = 1 then done
*/
if ((c->b == 0xa6) || (c->b == 0xa7) ||
(c->b == 0xae) || (c->b == 0xaf)) {
(c->b == 0xae) || (c->b == 0xaf)) {
if ((c->rep_prefix == REPE_PREFIX) &&
((ctxt->eflags & EFLG_ZF) == 0)) {
kvm_rip_write(ctxt->vcpu, c->eip);
goto done;
}
((ctxt->eflags & EFLG_ZF) == 0))
goto string_done;
if ((c->rep_prefix == REPNE_PREFIX) &&
((ctxt->eflags & EFLG_ZF) == EFLG_ZF)) {
kvm_rip_write(ctxt->vcpu, c->eip);
goto done;
}
((ctxt->eflags & EFLG_ZF) == EFLG_ZF))
goto string_done;
}
c->eip = ctxt->eip;
}
@ -2911,6 +2914,12 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
if (rc != X86EMUL_CONTINUE)
goto done;
/*
* restore dst type in case the decoding will be reused
* (happens for string instruction )
*/
c->dst.type = saved_dst_type;
if ((c->d & SrcMask) == SrcSI)
string_addr_inc(ctxt, seg_override_base(ctxt, c), VCPU_REGS_RSI,
&c->src);
@ -2918,8 +2927,11 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
if ((c->d & DstMask) == DstDI)
string_addr_inc(ctxt, es_base(ctxt), VCPU_REGS_RDI, &c->dst);
if (c->rep_prefix && (c->d & String))
if (c->rep_prefix && (c->d & String)) {
register_address_increment(c, &c->regs[VCPU_REGS_RCX], -1);
if (!(c->regs[VCPU_REGS_RCX] & 0x3ff))
ctxt->restart = false;
}
/* Commit shadow register state. */
memcpy(ctxt->vcpu->arch.regs, c->regs, sizeof c->regs);

19
arch/x86/kvm/x86.c
View File

@ -3755,6 +3755,7 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
return EMULATE_DONE;
}
restart:
r = x86_emulate_insn(&vcpu->arch.emulate_ctxt, &emulate_ops);
shadow_mask = vcpu->arch.emulate_ctxt.interruptibility;
@ -3777,7 +3778,7 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
if (r) {
if (kvm_mmu_unprotect_page_virt(vcpu, cr2))
return EMULATE_DONE;
goto done;
if (!vcpu->mmio_needed) {
kvm_report_emulation_failure(vcpu, "mmio");
return EMULATE_FAIL;
@ -3792,6 +3793,13 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
return EMULATE_DO_MMIO;
}
done:
if (vcpu->arch.exception.pending)
vcpu->arch.emulate_ctxt.restart = false;
if (vcpu->arch.emulate_ctxt.restart)
goto restart;
return EMULATE_DONE;
}
EXPORT_SYMBOL_GPL(emulate_instruction);
@ -4560,6 +4568,15 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
goto out;
}
}
if (vcpu->arch.emulate_ctxt.restart) {
vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
r = emulate_instruction(vcpu, 0, 0, EMULTYPE_NO_DECODE);
srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
if (r == EMULATE_DO_MMIO) {
r = 0;
goto out;
}
}
if (kvm_run->exit_reason == KVM_EXIT_HYPERCALL)
kvm_register_write(vcpu, VCPU_REGS_RAX,
kvm_run->hypercall.ret);