From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [RFC PATCH 2/3] KVM: x86: use memory_prepare in fetch helper
 function
Date: Tue, 06 May 2014 11:46:02 +0200
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Cc: Marcelo Tosatti <mtosatti@redhat.com>,
	Gleb Natapov <gleb@kernel.org>, linux-kernel@vger.kernel.org
To: Bandan Das <bsd@redhat.com>, kvm@vger.kernel.org
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Il 06/05/2014 02:40, Bandan Das ha scritto:
> +		ret = ctxt->ops->memory_prepare(ctxt, addr, toread,
> +						exception, false,
> +						NULL, &uaddr);
> +		if (ret != X86EMUL_CONTINUE)
> +			return ret;
> +
> +		if (unlikely(kvm_is_error_hva(uaddr))) {
> +			r = X86EMUL_PROPAGATE_FAULT;
> +			return r;
> +		}

What you are doing here is basically optimizing 
kvm_read_guest_virt_helper because you know that all reads will be 
single-page and you do not need the "next_segment" in kvm_read_guest.
Good catch, but you can use kvm_read_guest_page instead of going through 
ctxt->ops->memory_prepare. :)

Paolo

> +		ret = __copy_from_user(data, (void __user *)uaddr, toread);