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

[Julien Grall <julien.grall@arm.com>]

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.

> +
>           /* Ultimately, handle is an array of 16 uint8_t, same as uuid */
>           libxl_uuid_copy(ctx, (libxl_uuid *)&create.handle, &info->uuid);
>   
> diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
> index 941bbff4fe..3ff19bc1ca 100644
> --- a/xen/arch/arm/domain.c
> +++ b/xen/arch/arm/domain.c
> @@ -673,7 +673,6 @@ int arch_domain_create(struct domain *d,
>   
>       ASSERT(config != NULL);
>   
> -    /* p2m_init relies on some value initialized by the IOMMU subsystem */

Even with this patch, I still think iommu_domain_init() is required before 
calling p2m_init(). For instance, this function will set the features flag.

>       if ( (rc = iommu_domain_init(d)) != 0 )
>           goto fail;

Cheers,

-- 
Julien Grall

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