Re: [PATCH 1/2] xen/arm: Convert runstate address during hypcall

From: Julien Grall <julien.grall.oss@gmail.com>
To: Stefano Stabellini <sstabellini@kernel.org>
Cc: "Wei Liu" <wl@xen.org>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Ian Jackson" <ian.jackson@eu.citrix.com>,
	"George Dunlap" <george.dunlap@citrix.com>,
	"Bertrand Marquis" <bertrand.marquis@arm.com>,
	"Jan Beulich" <jbeulich@suse.com>,
	xen-devel <xen-devel@lists.xenproject.org>, nd <nd@arm.com>,
	"Volodymyr Babchuk" <Volodymyr_Babchuk@epam.com>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [PATCH 1/2] xen/arm: Convert runstate address during hypcall
Date: Thu, 11 Jun 2020 19:24:35 +0100	[thread overview]
Message-ID: <CAJ=z9a3u7ztgSmJbhjVATrfJEBBVkHbZei6ydBQeV8nzdDFA3Q@mail.gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.21.2006111055360.2815@sstabellini-ThinkPad-T480s>

> > +        return -EINVAL;
> >      }
> >
> > -    __copy_to_guest(runstate_guest(v), &runstate, 1);
> > +    v->arch.runstate_guest.page = page;
> > +    v->arch.runstate_guest.offset = offset;
> > +
> > +    spin_unlock(&v->arch.runstate_guest.lock);
> > +
> > +    return 0;
> > +}
> > +
> > +
> > +/* Update per-VCPU guest runstate shared memory area (if registered). */
> > +static void update_runstate_area(struct vcpu *v)
> > +{
> > +    struct vcpu_runstate_info *guest_runstate;
> > +    void *p;
> > +
> > +    spin_lock(&v->arch.runstate_guest.lock);
> >
> > -    if ( guest_handle )
> > +    if ( v->arch.runstate_guest.page )
> >      {
> > -        runstate.state_entry_time &= ~XEN_RUNSTATE_UPDATE;
> > +        p = __map_domain_page(v->arch.runstate_guest.page);
> > +        guest_runstate = p + v->arch.runstate_guest.offset;
> > +
> > +        if ( VM_ASSIST(v->domain, runstate_update_flag) )
> > +        {
> > +            v->runstate.state_entry_time |= XEN_RUNSTATE_UPDATE;
> > +            guest_runstate->state_entry_time |= XEN_RUNSTATE_UPDATE;
>
> I think that this write to guest_runstate should use write_atomic or
> another atomic write operation.

I thought about suggesting the same, but  guest_copy_* helpers may not
do a single memory write to state_entry_time.
What are you trying to prevent with the write_atomic()?

Cheers,