Re: [PATCH 5/6] x86/pv: map and unmap page tables in mark_pv_pt_pages_rdonly

[Hongyan Xia <hx242@xxxxxxx>]

On Tue, 2020-04-28 at 16:55 +0100, Hongyan Xia wrote:
> On Tue, 2020-04-28 at 17:33 +0200, Jan Beulich wrote:
> > On 17.04.2020 11:52, Hongyan Xia wrote:
> > > --- a/xen/arch/x86/pv/dom0_build.c
> > > +++ b/xen/arch/x86/pv/dom0_build.c
> > > @@ -50,17 +50,17 @@ static __init void
> > > mark_pv_pt_pages_rdonly(struct domain *d,
> > >      unsigned long count;
> > >      struct page_info *page;
> > >      l4_pgentry_t *pl4e;
> > > -    l3_pgentry_t *pl3e;
> > > -    l2_pgentry_t *pl2e;
> > > -    l1_pgentry_t *pl1e;
> > > +    l3_pgentry_t *pl3e, *l3t;
> > > +    l2_pgentry_t *pl2e, *l2t;
> > > +    l1_pgentry_t *pl1e, *l1t;
> > 
> > I don't quite see why the new local variables get introduced:
> > unmap_domain_page(), iirc, is quite fine with a non-page-
> > aligned argument.
> 
> You are right, although in this function, where plXe points to may
> not
> be the page we want to unmap. When plXe becomes aligned and points to
> a
> new page, we actually want to unmap the page before it increments to
> an
> aligned value.

Hmm, we can just unmap(plXe - 1) if my logic is correct, and save 3
local variables.

Hongyan