Re: [Xen-devel] [PATCH v5 05/10] domain: introduce XEN_DOMCTL_CDF_iommu flag

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

> -----Original Message-----
> From: Julien Grall <julien.grall@arm.com>
> Sent: 14 August 2019 18:15
> To: Paul Durrant <Paul.Durrant@citrix.com>; xen-devel@lists.xenproject.org
> Cc: 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>; Konrad Rzeszutek Wilk
> <konrad.wilk@oracle.com>; Stefano Stabellini <sstabellini@kernel.org>; Tim (Xen.org) <tim@xen.org>;
> Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>; Roger Pau Monne <roger.pau@citrix.com>
> Subject: Re: [PATCH v5 05/10] domain: introduce XEN_DOMCTL_CDF_iommu flag
> 
> Hi Paul,
> 
> On 14/08/2019 15:26, Paul Durrant wrote:
> >> -----Original Message-----
> >> From: Julien Grall <julien.grall@arm.com>
> >> Sent: 14 August 2019 15:00
> >> To: Paul Durrant <Paul.Durrant@citrix.com>; xen-devel@lists.xenproject.org
> >> Cc: 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>; Konrad Rzeszutek Wilk
> >> <konrad.wilk@oracle.com>; Stefano Stabellini <sstabellini@kernel.org>; Tim (Xen.org) <tim@xen.org>;
> >> Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>; Roger Pau Monne <roger.pau@citrix.com>
> >> Subject: Re: [PATCH v5 05/10] domain: introduce XEN_DOMCTL_CDF_iommu flag
> >>
> >> Hi Paul,
> >>
> >> On 14/08/2019 14:38, 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>
> >>> ---
> >>> 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
> >>>
> >>> 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()
> >>> ---
> >>>    tools/libxl/libxl_create.c            | 8 ++++++++
> >>>    xen/arch/arm/domain.c                 | 1 -
> >>>    xen/arch/arm/setup.c                  | 3 +++
> >>>    xen/arch/x86/setup.c                  | 3 +++
> >>>    xen/common/domain.c                   | 9 ++++++++-
> >>>    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 +++++
> >>>    9 files changed, 37 insertions(+), 5 deletions(-)
> >>>
> >>> diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
> >>> index 03ce166f4f..050ef042cd 100644
> >>> --- a/tools/libxl/libxl_create.c
> >>> +++ b/tools/libxl/libxl_create.c
> >>> @@ -555,6 +555,7 @@ int libxl__domain_make(libxl__gc *gc, libxl_domain_config *d_config,
> >>>                .max_grant_frames = b_info->max_grant_frames,
> >>>                .max_maptrack_frames = b_info->max_maptrack_frames,
> >>>            };
> >>> +        libxl_physinfo physinfo;
> >>>
> >>>            if (info->type != LIBXL_DOMAIN_TYPE_PV) {
> >>>                create.flags |= XEN_DOMCTL_CDF_hvm_guest;
> >>> @@ -564,6 +565,13 @@ int libxl__domain_make(libxl__gc *gc, libxl_domain_config *d_config,
> >>>                    libxl_defbool_val(info->oos) ? 0 : XEN_DOMCTL_CDF_oos_off;
> >>>            }
> >>>
> >>> +        rc = libxl_get_physinfo(ctx, &physinfo);
> >>> +        if (rc < 0)
> >>> +            goto out;
> >>> +
> >>> +        if (physinfo.cap_hvm_directio)
> >>> +            create.flags |= XEN_DOMCTL_CDF_iommu;
> >>
> >> This is not going to work well on Arm as XEN_SYSCTL_PHYSCAP_directio is never set.
> >
> > Oh, that's true. I need to pull that into the common sysctl handler. It also looks like
> XEN_SYSCTL_PHYSCAP_hvm should always be set for too, but ARMs arch_do_physinfo() is completely empty
> at the moment.
> 
> Looking at the header (include/public/sysctl.h) it is pretty clear that the two
> PHYSCAP are x86 specific.
> 
> Even if Arm guests are based on the same concept as HVM/PVH guest. They are just
> called "Arm guest". We have always taken action so far to say they are HVM/PVH
> guest when presenting to the user. For instance, we strongly recommend to have
> the guest type in your configuration.
> 
> So I am not entirely sure we want to expose the capability for Arm. Otherwise a
> user may think it is fine to use "hvm" guest type.

Ok, yes I see the directio flag is listed as x86 too... I guess I'll have to forget this mechanism and hardcode the flag to the global iommu_enabled flag inside the hypervisor.

  Paul

> 
> Cheers,
> 
> --
> Julien Grall
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