linux-kernel - Re: [PATCH v2 10/12] KVM: selftests / xen: map shared

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Message-ID: <f75f1a112c58e072d05ca671100438587295e089.camel@infradead.org>
Date:   Mon, 18 Sep 2023 14:30:05 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     paul@....org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Paul Durrant <pdurrant@...zon.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v2 10/12] KVM: selftests / xen: map shared_info using
 HVA rather than GFN

On Mon, 2023-09-18 at 14:24 +0100, Paul Durrant wrote:
> On 18/09/2023 14:19, David Woodhouse wrote:
> > On Mon, 2023-09-18 at 11:21 +0000, Paul Durrant wrote:
> > > 
> > > -                               ret = pthread_create(&thread, NULL, &juggle_shinfo_state, (void *)vm);
> > > +                               if (has_shinfo_hva)
> > > +                                       ret = pthread_create(&thread, NULL,
> > > +                                                            &juggle_shinfo_state_hva, (void *)vm);
> > > +                               else
> > > +                                       ret = pthread_create(&thread, NULL,
> > > +                                                            &juggle_shinfo_state_gfn, (void *)vm);
> > >                                  TEST_ASSERT(ret == 0, "pthread_create() failed: %s", strerror(ret));
> > >   
> > 
> > 
> > This means you don't exercise the GFN-based path (which all current VMM
> > implementations use) on newer kernels. Could you have a single
> > juggle_shinfo_state() function as before, but make it repeatedly set
> > and clear the shinfo using *both* HVA and GFN (if the former is
> > available, of course).
> 
> The guidance is to use HVA if the feature is available; a VMM should not 
> really be mixing and matching. That said, setting it either way should 
> be equivalent.

Sure, but this isn't really a VMM; it's a test harness to exercise a
bunch of ioctls. One of which it no longer bothers to test now, if the
new variant exists.

If we're going to keep the old API we should also continue to *test*
the old API. (And we should).


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