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Commit 5cd21917 authored by Gleb Natapov's avatar Gleb Natapov Committed by Avi Kivity
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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: default avatarGleb Natapov <gleb@redhat.com>
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
parent cb404fe0

arch/x86/include/asm/kvm_emulate.h

+1 −0
Original line number Diff line number Diff line
@@ -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;

};

arch/x86/kvm/emulate.c

+23 −11
Original line number Diff line number Diff line
@@ -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;

		}
@@ -2469,15 +2476,11 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops) 
		if ((c->b == 0xa6) || (c->b == 0xa7) ||

		    (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);

arch/x86/kvm/x86.c

+18 −1
Original line number Diff line number Diff line
@@ -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);