Re: [PATCH 2/2] KVM: x86 emulator: Discard CR2 in x86 emulator

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Sheng Yang wrote:
> From 9cd9d5cde7341d5e9de41b1070cea7a98e7d8cc9 Mon Sep 17 00:00:00 2001
> From: Sheng Yang <sheng.yang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
> Date: Thu, 15 Nov 2007 15:11:58 +0800
> Subject: [PATCH 2/2] KVM: x86 emulator: Discard CR2 in x86 emulator
>
> For CR2 is unreliable and unavailable in many condition, this patch
> completely decode memory operand instead of using CR2 in x86 emulator.
>
>
>   

One of my innermost wishes...

> diff --git a/drivers/kvm/x86.c b/drivers/kvm/x86.c
> index aa6c3d8..85a0776 100644
> --- a/drivers/kvm/x86.c
> +++ b/drivers/kvm/x86.c
> @@ -1293,7 +1293,7 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
>  
>  		vcpu->emulate_ctxt.vcpu = vcpu;
>  		vcpu->emulate_ctxt.eflags = kvm_x86_ops->get_rflags(vcpu);
> -		vcpu->emulate_ctxt.cr2 = cr2;
> +		vcpu->emulate_ctxt.memop = 0;
>   

We have c->modrm_ea which can be used for the memory operand.

> diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
> index c020010..95536a8 100644
> --- a/drivers/kvm/x86_emulate.c
> +++ b/drivers/kvm/x86_emulate.c
> @@ -880,6 +880,8 @@ done_prefixes:
>  			break;
>  		}
>  		c->src.type = OP_MEM;
> +		ctxt->memop = insn_fetch(u32, c->src.bytes, c->eip);
> +		c->eip -= c->src.bytes; /* keep the page fault ip */
>   

I don't understand this.  In the cases where the memory operand address 
is encoded in the instruction, we fetch it explicity.  When it isn't, 
this is broken.

>  		break;
>  	case SrcImm:
>  		c->src.type = OP_IMM;
> @@ -918,14 +920,18 @@ done_prefixes:
>  			 c->twobyte && (c->b == 0xb6 || c->b == 0xb7));
>  		break;
>  	case DstMem:
> +		c->dst.bytes = (c->d & ByteOp) ? 1 : c->op_bytes;
>   

This seems unrelated; needs a separate patch.  Please check that movzx 
and movsx aren't affected by this.

>  		/*
>  		 * For instructions with a ModR/M byte, switch to register
>  		 * access if Mod = 3.
>  		 */
> -		if ((c->d & ModRM) && c->modrm_mod == 3)
> +		if ((c->d & ModRM) && c->modrm_mod == 3) {
>  			c->dst.type = OP_REG;
> -		else
> -			c->dst.type = OP_MEM;
> +			break;
> +		}
> +		c->dst.type = OP_MEM;
> +		ctxt->memop = insn_fetch(u32, c->dst.bytes, c->eip);
> +		c->eip -= c->dst.bytes; /* keep the page fault ip */
>   

Ditto.

 	


-- 
error compiling committee.c: too many arguments to function


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