Hi Jan Sorry about the late reply, got sidetracked a few weeks.
> -----Original Message----- > From: Jan Beulich <jbeul...@suse.com> > Sent: Wednesday, May 18, 2022 2:36 PM > To: Penny Zheng <penny.zh...@arm.com> > Cc: Wei Chen <wei.c...@arm.com>; Stefano Stabellini > <sstabell...@kernel.org>; Julien Grall <jul...@xen.org>; Bertrand Marquis > <bertrand.marq...@arm.com>; Volodymyr Babchuk > <volodymyr_babc...@epam.com>; Andrew Cooper > <andrew.coop...@citrix.com>; George Dunlap <george.dun...@citrix.com>; > Wei Liu <w...@xen.org>; xen-devel@lists.xenproject.org > Subject: Re: [PATCH v4 2/8] xen/arm: allocate static shared memory to the > default owner dom_io > > On 18.05.2022 05:14, Penny Zheng wrote: > > Hi Jan > > > >> -----Original Message----- > >> From: Jan Beulich <jbeul...@suse.com> > >> Sent: Wednesday, May 18, 2022 12:01 AM > >> To: Penny Zheng <penny.zh...@arm.com> > >> Cc: Wei Chen <wei.c...@arm.com>; Stefano Stabellini > >> <sstabell...@kernel.org>; Julien Grall <jul...@xen.org>; Bertrand > >> Marquis <bertrand.marq...@arm.com>; Volodymyr Babchuk > >> <volodymyr_babc...@epam.com>; Andrew Cooper > >> <andrew.coop...@citrix.com>; George Dunlap > >> <george.dun...@citrix.com>; Wei Liu <w...@xen.org>; > >> xen-devel@lists.xenproject.org > >> Subject: Re: [PATCH v4 2/8] xen/arm: allocate static shared memory to > >> the default owner dom_io > >> > >> On 17.05.2022 11:05, Penny Zheng wrote: > >>> --- a/xen/common/domain.c > >>> +++ b/xen/common/domain.c > >>> @@ -780,6 +780,11 @@ void __init setup_system_domains(void) > >>> * This domain owns I/O pages that are within the range of the > page_info > >>> * array. Mappings occur at the priv of the caller. > >>> * Quarantined PCI devices will be associated with this domain. > >>> + * > >>> + * DOMID_IO could also be used for mapping memory when no explicit > >>> + * domain is specified. > >>> + * For instance, DOMID_IO is the owner of memory pre-shared among > >>> + * multiple domains at boot time, when no explicit owner is > >>> specified. > >>> */ > >>> dom_io = domain_create(DOMID_IO, NULL, 0); > >>> if ( IS_ERR(dom_io) ) > >> > >> I'm sorry: The comment change is definitely better now than it was, > >> but it is still written in a way requiring further knowledge to > >> understand what it talks about. Without further context, "when no > >> explicit domain is specified" only raises questions. I would have > >> tried to make a suggestion, but I can't really figure what it is that you > >> want > to get across here. > > > > How about I only retain the "For instance, xxx" and make it more in details. > > " > > DOMID_IO is also the default owner of memory pre-shared among multiple > > domains at boot time, when no explicit owner is specified with "owner" > > property in static shared memory device node. See section > > docs/misc/arm/device-tree/booting.txt: Static Shared Memory for more > details. > > " > > This reads quite a bit better. Yet I continue to be puzzled about the apparent > conflict of "pre-shared" and "no explicit owner": How can memory be (pre- > )shared when the owner isn't known? Shouldn't all memory have an owner? > Or alternatively if this sharing model doesn't require ownership, shouldn't > all > shared memory be owned by DomIO? In any event, to leave such details out of > here, perhaps the comment could consist of just the first part of what you > wrote, ending at where the first comma is? > We have a short discussion about the memory ownership on my design link( https://lore.kernel.org/all/a50d9fde-1d06-7cda-2779-9eea9e1c0...@xen.org/T/) , we have user cases for both scenario. Ok, I will modify the comment and only keep " DOMID_IO is also the default owner of memory pre-shared among multiple domains at boot time. " > Jan
