Re: [Xen-devel] [PATCH 2/3] x86 / hvm: add domain_relinquish_resources() method

[Jan Beulich <jbeulich@xxxxxxxx>]

On 22.01.2020 16:56, Durrant, Paul wrote:
>> -----Original Message-----
>> From: Jan Beulich <jbeulich@xxxxxxxx>
>> Sent: 22 January 2020 15:51
>> To: Durrant, Paul <pdurrant@xxxxxxxxxxxx>
>> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; Andrew Cooper
>> <andrew.cooper3@xxxxxxxxxx>; Wei Liu <wl@xxxxxxx>; Roger Pau Monné
>> <roger.pau@xxxxxxxxxx>; Jun Nakajima <jun.nakajima@xxxxxxxxx>; Kevin Tian
>> <kevin.tian@xxxxxxxxx>
>> Subject: Re: [PATCH 2/3] x86 / hvm: add domain_relinquish_resources()
>> method
>>
>> On 21.01.2020 13:00, Paul Durrant wrote:
>>> There are two functions in hvm.c to deal with tear-down and a domain:
>>> hvm_domain_relinquish_resources() and hvm_domain_destroy(). However,
>> only
>>> the latter has an associated method in 'hvm_funcs'. This patch adds
>>> a method for the former and stub definitions for SVM and VMX.
>>
>> Why the stubs? Simply ...
>>
>>> --- a/xen/arch/x86/hvm/hvm.c
>>> +++ b/xen/arch/x86/hvm/hvm.c
>>> @@ -715,6 +715,8 @@ int hvm_domain_initialise(struct domain *d)
>>>
>>>  void hvm_domain_relinquish_resources(struct domain *d)
>>>  {
>>> +    hvm_funcs.domain_relinquish_resources(d);
>>
>> ... stick a NULL check around this one. I also wonder whether, it
>> being entirely new, this wouldn't better use alternative call
>> patching right from the beginning. It's not the hottest path, but
>> avoiding indirect calls seems quite desirable, especially when
>> doing so is relatively cheap.
>>
> 
> I'd like it to align with the rest of the hvm_funcs so I'll add the
> NULL check, but alternatives patch for all hvm_funcs seems like a
> good thing I the longer term.

The frequently used ones have been converted already. Hence my
suggestion to make new ones use that model from the beginning.

Jan

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