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

["Durrant, Paul" <pdurrant@xxxxxxxxxxxx>]

> -----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.

  Paul
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