From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vitaly Kuznetsov Subject: Re: [PATCH v4] x86/arm/mm: use gfn instead of pfn in p2m_get_mem_access/p2m_set_mem_access Date: Thu, 02 Jul 2015 14:26:02 +0200 Message-ID: <87wpyirbj9.fsf@vitty.brq.redhat.com> References: <1435592708-26456-1-git-send-email-vkuznets@redhat.com> <559516F9.8050402@eu.citrix.com> <55951BDC.7010002@citrix.com> <20150702112549.GA87948@deinos.phlegethon.org> <55952138.3070501@eu.citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <55952138.3070501@eu.citrix.com> (George Dunlap's message of "Thu, 2 Jul 2015 12:32:08 +0100") List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: George Dunlap Cc: Keir Fraser , Ian Campbell , Razvan Cojocaru , Andrew Cooper , Tim Deegan , xen-devel@lists.xen.org, Stefano Stabellini , Jan Beulich , Tamas K Lengyel List-Id: xen-devel@lists.xenproject.org George Dunlap writes: > On 07/02/2015 12:25 PM, Tim Deegan wrote: >> At 12:09 +0100 on 02 Jul (1435838956), Andrew Cooper wrote: >>> On 02/07/15 11:48, George Dunlap wrote: >>>> Now in p2m_set_mem_access(), rather than just using an unsigned long in >>>> the loop iterating over gfns, you do this thing where you convert gfn_t >>>> to unsigned long, add one, and then convert it back to gfn_t again. >>>> >>>> I can't see any comments in v3 that suggest you doing that, and it seems >>>> a bit clunky. Is that really necessary? Wouldn't it be better to >>>> declare a local variable? >>>> >>>> I'm not strongly opinionated on this one, it just seems a bit strange. >>>> >>>> Everything else looks good, thanks. >>> >>> Looping over {g,m,p}fn_t's is indeed awkward, as the compiler tricks for >>> typesafety don't allow for simply adding 1 to a typesafe variable. >>> >>> In a cases like this, I think it is acceptable to keep a unsigned long >>> shadow variable and manipulate it is a plain integer. The eventual >>> _gfn() required to pass it further down the callchain will help to >>> visually re-enforce the appropriate type. >>> >>> After all, the entire point of these typesafes are to try and avoid >>> accidentally mixing up the different address spaces, but a function >>> which takes a typesafe, loops over a subset and passes the same typesafe >>> further down can probably be trusted to DTRT, catching errors at review >>> time. >>> >>> Off the top of my head, the only functions which would normally expect >>> to mix and match the typesafes are the pagetable walking ones. >> >> It should be easy enough to extend the macros to define a >> gfn_inc(&gfn_t) operator for this kind of thing. > > I was thinking that -- although in this case you'd still need to un-pack > it to do the loop exit conditional. To really make things pretty you'd > want a for_gfn_range() macro or something like that that takes a start > gfn and a number. > > But that's really starting to be feature creep for this patch, which is > why I didn't want to suggest it on v4. :-) Well, if you look at what I was fixing in v1 ... :-) I suggest we add a local unsigned long here and close the deal, when {g,m,p}fn_{inc,dec} macros are available we'll get rid of it. -- Vitaly