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

From: "Durrant, Paul" <pdurrant@amazon.co.uk>
To: Jan Beulich <jbeulich@suse.com>
Cc: "Kevin Tian" <kevin.tian@intel.com>, "Wei Liu" <wl@xen.org>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Jun Nakajima" <jun.nakajima@intel.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH 2/3] x86 / hvm: add domain_relinquish_resources() method
Date: Wed, 22 Jan 2020 15:56:42 +0000	[thread overview]
Message-ID: <9ad0b7eec02945dba00017f3bfe85730@EX13D32EUC003.ant.amazon.com> (raw)
In-Reply-To: <018a1293-ad4f-44e3-ab73-90491077e434@suse.com>

> -----Original Message-----
> From: Jan Beulich <jbeulich@suse.com>
> Sent: 22 January 2020 15:51
> To: Durrant, Paul <pdurrant@amazon.co.uk>
> Cc: xen-devel@lists.xenproject.org; Andrew Cooper
> <andrew.cooper3@citrix.com>; Wei Liu <wl@xen.org>; Roger Pau Monné
> <roger.pau@citrix.com>; Jun Nakajima <jun.nakajima@intel.com>; Kevin Tian
> <kevin.tian@intel.com>
> 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
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel