Re: [Xen-devel] [PATCH 4/5] mm: Don't request scrubbing until dom0 is running

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Aug 30, 2017 at 10:19:49AM -0400, Boris Ostrovsky wrote:
> On 08/30/2017 04:42 AM, Wei Liu wrote:
> > On Tue, Aug 29, 2017 at 01:09:16PM -0400, Boris Ostrovsky wrote:
> >> There is no need to scrub pages freed during dom0 construction
> >> since heap will be scrubbed once dom0 is ready (by scrub_heap_pages()).
> >>
> >> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> >> ---
> >> Changes in v2:
> >> * Removed '#ifdef CONFIG_SCRUB_DEBUG'
> >>
> >>  xen/common/page_alloc.c | 6 +-----
> >>  1 file changed, 1 insertion(+), 5 deletions(-)
> >>
> >> diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
> >> index 3db77c5..6c08983 100644
> >> --- a/xen/common/page_alloc.c
> >> +++ b/xen/common/page_alloc.c
> >> @@ -2247,16 +2247,12 @@ void free_domheap_pages(struct page_info *pg, 
> >> unsigned int order)
> >>  
> >>              spin_unlock_recursive(&d->page_alloc_lock);
> >>  
> >> -#ifndef CONFIG_SCRUB_DEBUG
> >>              /*
> >>               * Normally we expect a domain to clear pages before freeing 
> >> them,
> >>               * if it cares about the secrecy of their contents. However, 
> >> after
> >>               * a domain has died we assume responsibility for erasure.
> >>               */
> >> -            scrub = !!d->is_dying;
> >> -#else
> >> -            scrub = true;
> >> -#endif
> >> +            scrub = !!d->is_dying | scrub_debug;
> > Use logical or here please. And the !! for is_dying is not necessary.
> 
> Yes, I'll change this.
> 
> >
> > Also please expand the comment to say why scrub_debug is also checked.
> 
> TBH, I think variable name (scrub_debug) should be sufficient. I could
> say something like "when scrub debugging is on we always scrub" but I am
> not sure how useful that would be. (Previous name, boot_scrub_done,
> would have indeed be helped by a comment).
> 

Hmm... OK, I won't insist on this.

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