Re: [Xen-devel] [PATCH v6 06/10] domain: introduce XEN_DOMCTL_CDF_iommu flag

[Paul Durrant <Paul.Durrant@citrix.com>]

> -----Original Message-----
> From: Roger Pau Monne <roger.pau@citrix.com>
> Sent: 23 August 2019 11:33
> To: Paul Durrant <Paul.Durrant@citrix.com>
> Cc: xen-devel@lists.xenproject.org; Ian Jackson <Ian.Jackson@citrix.com>; Wei Liu <wl@xen.org>;
> Anthony Perard <anthony.perard@citrix.com>; Andrew Cooper <Andrew.Cooper3@citrix.com>; George Dunlap
> <George.Dunlap@citrix.com>; Jan Beulich <jbeulich@suse.com>; Julien Grall <julien.grall@arm.com>;
> Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>; Stefano Stabellini <sstabellini@kernel.org>; Tim
> (Xen.org) <tim@xen.org>; Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
> Subject: Re: [PATCH v6 06/10] domain: introduce XEN_DOMCTL_CDF_iommu flag
> 
> On Fri, Aug 16, 2019 at 06:19:57PM +0100, Paul Durrant wrote:
> > This patch introduces a common domain creation flag to determine whether
> > the domain is permitted to make use of the IOMMU. Currently the flag is
> > always set (for both dom0 and domU) if the IOMMU is globally enabled
> > (i.e. iommu_enabled == 1). sanitise_domain_config() is modified to reject
> > the flag if !iommu_enabled.
> >
> > A new helper function, is_iommu_enabled(), is added to test the flag and
> > iommu_domain_init() will return immediately if !is_iommu_enabled(). This is
> > slightly different to the previous behaviour based on !iommu_enabled where
> > the call to arch_iommu_domain_init() was made regardless, however it appears
> > that this call was only necessary to initialize the dt_devices list for ARM
> > such that iommu_release_dt_devices() can be called unconditionally by
> > domain_relinquish_resources(). Adding a simple check of is_iommu_enabled()
> > into iommu_release_dt_devices() keeps this unconditional call working.
> >
> > No functional change should be observed with this patch applied.
> >
> > Subsequent patches will allow the toolstack to control whether use of the
> > IOMMU is enabled for a domain.
> >
> > NOTE: The introduction of the is_iommu_enabled() helper function might
> >       seem excessive but its use is expected to increase with subsequent
> >       patches. Also, having iommu_domain_init() bail before calling
> >       arch_iommu_domain_init() is not strictly necessary, but I think the
> >       consequent addition of the call to is_iommu_enabled() in
> >       iommu_release_dt_devices() makes the code clearer.
> >
> > Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
> 
> I have one ARM-related question and one 'nice to have', but the code
> LGTM:
> 
> Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
> 
> > ---
> > Cc: Ian Jackson <ian.jackson@eu.citrix.com>
> > Cc: Wei Liu <wl@xen.org>
> > Cc: Anthony PERARD <anthony.perard@citrix.com>
> > Cc: Andrew Cooper <andrew.cooper3@citrix.com>
> > Cc: George Dunlap <George.Dunlap@eu.citrix.com>
> > Cc: Jan Beulich <jbeulich@suse.com>
> > Cc: Julien Grall <julien.grall@arm.com>
> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> > Cc: Stefano Stabellini <sstabellini@kernel.org>
> > Cc: Tim Deegan <tim@xen.org>
> > Cc: Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
> > Cc: "Roger Pau Monné" <roger.pau@citrix.com>
> >
> > Previously part of series https://lists.xenproject.org/archives/html/xen-devel/2019-07/msg02267.html
> >
> > v6:
> >  - Remove the toolstack parts as there's no nice method of testing whether
> >    the IOMMU is enabled in an architecture-neutral way
> >
> > v5:
> >  - Move is_iommu_enabled() check into iommu_domain_init()
> >  - Reject XEN_DOMCTL_CDF_iommu in sanitise_domain_config() if !iommu_enabled
> >  - Use evaluate_nospec() in defintion of is_iommu_enabled()
> > ---
> >  xen/arch/arm/setup.c                  | 3 +++
> >  xen/arch/x86/setup.c                  | 3 +++
> >  xen/common/domain.c                   | 9 ++++++++-
> >  xen/common/domctl.c                   | 8 ++++++++
> >  xen/drivers/passthrough/device_tree.c | 3 +++
> >  xen/drivers/passthrough/iommu.c       | 6 +++---
> >  xen/include/public/domctl.h           | 4 ++++
> >  xen/include/xen/sched.h               | 5 +++++
> >  8 files changed, 37 insertions(+), 4 deletions(-)
> >
> > diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> > index 2c5d1372c0..20021ee0ca 100644
> > --- a/xen/arch/arm/setup.c
> > +++ b/xen/arch/arm/setup.c
> > @@ -914,6 +914,9 @@ void __init start_xen(unsigned long boot_phys_offset,
> >      dom0_cfg.arch.tee_type = tee_get_type();
> >      dom0_cfg.max_vcpus = dom0_max_vcpus();
> >
> > +    if ( iommu_enabled )
> > +        dom0_cfg.flags |= XEN_DOMCTL_CDF_iommu;
> > +
> >      dom0 = domain_create(0, &dom0_cfg, true);
> >      if ( IS_ERR(dom0) || (alloc_dom0_vcpu0(dom0) == NULL) )
> >          panic("Error creating domain 0\n");
> > diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
> > index d0b35b0ce2..fa226a2bab 100644
> > --- a/xen/arch/x86/setup.c
> > +++ b/xen/arch/x86/setup.c
> > @@ -1733,6 +1733,9 @@ void __init noreturn __start_xen(unsigned long mbi_p)
> >      }
> >      dom0_cfg.max_vcpus = dom0_max_vcpus();
> >
> > +    if ( iommu_enabled )
> > +        dom0_cfg.flags |= XEN_DOMCTL_CDF_iommu;
> > +
> >      /* Create initial domain 0. */
> >      dom0 = domain_create(get_initial_domain_id(), &dom0_cfg, !pv_shim);
> >      if ( IS_ERR(dom0) || (alloc_dom0_vcpu0(dom0) == NULL) )
> > diff --git a/xen/common/domain.c b/xen/common/domain.c
> > index 76e6976617..e832a5c4aa 100644
> > --- a/xen/common/domain.c
> > +++ b/xen/common/domain.c
> > @@ -301,7 +301,8 @@ static int sanitise_domain_config(struct xen_domctl_createdomain *config)
> >                             XEN_DOMCTL_CDF_hap |
> >                             XEN_DOMCTL_CDF_s3_integrity |
> >                             XEN_DOMCTL_CDF_oos_off |
> > -                           XEN_DOMCTL_CDF_xs_domain) )
> > +                           XEN_DOMCTL_CDF_xs_domain |
> > +                           XEN_DOMCTL_CDF_iommu) )
> >      {
> >          dprintk(XENLOG_INFO, "Unknown CDF flags %#x\n", config->flags);
> >          return -EINVAL;
> > @@ -328,6 +329,12 @@ static int sanitise_domain_config(struct xen_domctl_createdomain *config)
> >          config->flags |= XEN_DOMCTL_CDF_oos_off;
> >      }
> >
> > +    if ( (config->flags & XEN_DOMCTL_CDF_iommu) && !iommu_enabled )
> > +    {
> > +        dprintk(XENLOG_INFO, "IOMMU is not enabled\n");
> > +        return -EINVAL;
> > +    }
> > +
> >      return arch_sanitise_domain_config(config);
> >  }
> >
> > diff --git a/xen/common/domctl.c b/xen/common/domctl.c
> > index 6e6e9b9866..fddf20f1b5 100644
> > --- a/xen/common/domctl.c
> > +++ b/xen/common/domctl.c
> > @@ -515,6 +515,14 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
> >              rover = dom;
> >          }
> >
> > +        /*
> > +         * For now, make sure the createdomain IOMMU flag is set if the
> > +         * IOMMU is enabled. When the flag comes under toolstack control
> > +         * this can go away.
> > +         */
> > +        if ( iommu_enabled )
> > +            op->u.createdomain.flags |= XEN_DOMCTL_CDF_iommu;
> 
> Can you add some kind of safety check here to make sure this bodge is
> removed when the toolstack takes control of the flag, ie:
> 
> BUG_ON(op->u.createdomain.flags & XEN_DOMCTL_CDF_iommu);
> 
> Or maybe an ASSERT_UNREACHABLE() followed by returning EINVAL?

Ok, the former is a bit severe so I think I'll go for the latter.

> 
> > +
> >          d = domain_create(dom, &op->u.createdomain, false);
> >          if ( IS_ERR(d) )
> >          {
> > diff --git a/xen/drivers/passthrough/device_tree.c b/xen/drivers/passthrough/device_tree.c
> > index b6eaae7283..d32b172664 100644
> > --- a/xen/drivers/passthrough/device_tree.c
> > +++ b/xen/drivers/passthrough/device_tree.c
> > @@ -119,6 +119,9 @@ int iommu_release_dt_devices(struct domain *d)
> >      struct dt_device_node *dev, *_dev;
> >      int rc;
> >
> > +    if ( !is_iommu_enabled(d) )
> > +        return 0;
> 
> How could you get here? If the domain doesn't have an iommu how did it
> got the devices assigned in the first place?
> 

As I say in the commit comment, iommu_release_dt_device() is called unconditionally from domain_relinquish_resources().

> The hardware domain on ARM would be an exception here, since it uses
> an identity second stage translation, but I don't think
> iommu_release_dt_devices is ever used against the hardware domain.
> 

No, it is only called from domain_relinquish_resources() so should not apply to the h/w domain.

  Paul

> Thanks, Roger.

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