Re: [Xen-devel] [PATCH v2 17/19] x86/hvm: Avoid __hvm_copy() raising #PF behind the emulators back

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 28/11/16 13:01, Paul Durrant wrote:
>> -----Original Message-----
>> From: Andrew Cooper
>> Sent: 28 November 2016 12:58
>> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>; Xen-devel <xen-
>> devel@xxxxxxxxxxxxx>
>> Cc: Jan Beulich <JBeulich@xxxxxxxx>; Tim (Xen.org) <tim@xxxxxxx>; Jun
>> Nakajima <jun.nakajima@xxxxxxxxx>; Kevin Tian <kevin.tian@xxxxxxxxx>
>> Subject: Re: [PATCH v2 17/19] x86/hvm: Avoid __hvm_copy() raising #PF
>> behind the emulators back
>>
>> On 28/11/16 11:56, Paul Durrant wrote:
>>>> -----Original Message-----
>>>> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
>>>> Sent: 28 November 2016 11:14
>>>> To: Xen-devel <xen-devel@xxxxxxxxxxxxx>
>>>> Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Jan Beulich
>>>> <JBeulich@xxxxxxxx>; Paul Durrant <Paul.Durrant@xxxxxxxxxx>; Tim
>>>> (Xen.org) <tim@xxxxxxx>; Jun Nakajima <jun.nakajima@xxxxxxxxx>;
>> Kevin
>>>> Tian <kevin.tian@xxxxxxxxx>
>>>> Subject: [PATCH v2 17/19] x86/hvm: Avoid __hvm_copy() raising #PF
>> behind
>>>> the emulators back
>>>>
>>>> Drop the call to hvm_inject_page_fault() in __hvm_copy(), and require
>>>> callers
>>>> to inject the pagefault themselves.
>>>>
>>>> No functional change.
>>> That's not the way it looks on the face of it. You've indeed removed the 
>>> call
>> to hvm_inject_page_fault() but some of the callers now call
>> x86_emul_pagefault(). I'd call that a functional change... clearly the change
>> you intended, but still a functional change.
>>
>> Hmm - I suppose I am confusing no functional change in the hypervisor
>> with no functional change as observed by a guest.
>>
> Yes, I was thinking from the PoV of someone looking at this patch years later 
> and saying 'hang on a minute...'. Saying 'no guest-observable behavioural 
> change' is much clearer I think.

I will double check all of the patches and clarify it in the commit
messages.

~Andrew

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