linux-kernel - Re: [PATCH 2/9] KVM: x86: simplify read

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Date:	Fri, 20 Jul 2012 10:17:36 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 2/9] KVM: x86: simplify read_emulated

On 07/20/2012 07:58 AM, Marcelo Tosatti wrote:

>> -	}
>> +	rc = ctxt->ops->read_emulated(ctxt, addr, mc->data + mc->end, size,
>> +				      &ctxt->exception);
>> +	if (rc != X86EMUL_CONTINUE)
>> +		return rc;
>> +
>> +	mc->end += size;
>> +
>> +read_cached:
>> +	memcpy(dest, mc->data + mc->pos, size);
> 
> What prevents read_emulated(size > 8) call, with
> mc->pos == (mc->end - 8) now?

Marcelo,

The splitting has been done in emulator_read_write_onepage:

	while (bytes) {
		unsigned now = min(bytes, 8U);

		frag = &vcpu->mmio_fragments[vcpu->mmio_nr_fragments++];
		frag->gpa = gpa;
		frag->data = val;
		frag->len = now;
		frag->write_readonly_mem = (ret == -EPERM);

		gpa += now;
		val += now;
		bytes -= now;
	}

So i think it is safe to remove the splitting in read_emulated.

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