Re: [Xen-devel] [PATCH v4 05/18] x86/mem_sharing: don't try to unshare twice during page fault

[Tamas K Lengyel <tamas.k.lengyel@xxxxxxxxx>]

On Thu, Jan 16, 2020 at 7:55 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>
> On 08.01.2020 18:14, Tamas K Lengyel wrote:
> > @@ -1702,11 +1703,14 @@ int hvm_hap_nested_page_fault(paddr_t gpa, unsigned 
> > long gla,
> >      struct domain *currd = curr->domain;
> >      struct p2m_domain *p2m, *hostp2m;
> >      int rc, fall_through = 0, paged = 0;
> > -    int sharing_enomem = 0;
> >      vm_event_request_t *req_ptr = NULL;
> >      bool sync = false;
> >      unsigned int page_order;
> >
> > +#ifdef CONFIG_MEM_SHARING
> > +    bool sharing_enomem = false;
> > +#endif
>
> To reduce #ifdef-ary, could you leave this alone (or convert to
> bool in place, without #ifdef) and ...
>
> > @@ -1955,19 +1961,21 @@ int hvm_hap_nested_page_fault(paddr_t gpa, unsigned 
> > long gla,
> >       */
> >      if ( paged )
> >          p2m_mem_paging_populate(currd, gfn);
> > +
> > +#ifdef CONFIG_MEM_SHARING
> >      if ( sharing_enomem )
> >      {
> > -        int rv;
> > -
> > -        if ( (rv = mem_sharing_notify_enomem(currd, gfn, true)) < 0 )
> > +        if ( !vm_event_check_ring(currd->vm_event_share) )
> >          {
> > -            gdprintk(XENLOG_ERR, "Domain %hu attempt to unshare "
> > -                     "gfn %lx, ENOMEM and no helper (rc %d)\n",
> > -                     currd->domain_id, gfn, rv);
> > +            gprintk(XENLOG_ERR, "Domain %pd attempt to unshare "
> > +                    "gfn %lx, ENOMEM and no helper\n",
> > +                    currd, gfn);
> >              /* Crash the domain */
> >              rc = 0;
> >          }
> >      }
> > +#endif
>
> ... move the #ifdef inside the braces here? With this
> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

SGTM, I assume you are counting on the compiler to just get rid of the
variable when it sees its never used?

Thanks,
Tamas

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