Re: [Xen-devel] [PATCH v3 2/4] x86/mem_sharing: introduce and use page_lock_memshr instead of page_lock

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Tue, Apr 30, 2019 at 2:44 AM Jan Beulich <JBeulich@xxxxxxxx> wrote:
>
> >>> On 30.04.19 at 10:28, <tamas@xxxxxxxxxxxxx> wrote:
> > On Tue, Apr 30, 2019 at 1:15 AM Jan Beulich <JBeulich@xxxxxxxx> wrote:
> >>
> >> >>> On 29.04.19 at 18:35, <tamas@xxxxxxxxxxxxx> wrote:
> >> > On Mon, Apr 29, 2019 at 9:18 AM Jan Beulich <JBeulich@xxxxxxxx> wrote:
> >> >> >>> On 26.04.19 at 19:21, <tamas@xxxxxxxxxxxxx> wrote:
> >> >> > --- a/xen/arch/x86/mm.c
> >> >> > +++ b/xen/arch/x86/mm.c
> >> >> > @@ -2030,12 +2030,11 @@ static inline bool
> > current_locked_page_ne_check(struct page_info *page) {
> >> >> >  #define current_locked_page_ne_check(x) true
> >> >> >  #endif
> >> >> >
> >> >> > -int page_lock(struct page_info *page)
> >> >> > +#if defined(CONFIG_PV) || defined(CONFIG_HAS_MEM_SHARING)
> >> >> > +static int _page_lock(struct page_info *page)
> >> >>
> >> >> As per above, personally I'm against introducing
> >> >> page_{,un}lock_memshr(), as that makes the abuse even more
> >> >> look like proper use. But if this was to be kept this way, may I
> >> >> ask that you switch int -> bool in the return types at this occasion?
> >> >
> >> > Switching them to bool would be fine. Replacing them with something
> >> > saner is unfortunately out-of-scope at the moment. Unless someone has
> >> > a specific solution that can be put in place. I don't have one.
> >>
> >> I've outlined a solution already: Make a mem-sharing private variant
> >> of page_{,un}lock(), derived from the PV ones (but with pieces
> >> dropped you don't want/need).
> >
> > Well, that's what I already did here in this patch. No?
>
> No - you've retained a shared _page_{,un}lock(), whereas my
> suggestion was to have a completely independent pair of
> functions in mem_sharing.c. The only thing needed by both PV
> and HVM would then be the PGT_locked flag.

I see. Sure.

Tamas

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