Re: [PATCH v4 1/2] xen/passthrough: Provide stub functions when !HAS_PASSTHROUGH

[Julien Grall <julien@xxxxxxx>]

Hi Luca,

On 07/03/2025 07:58, Luca Fancellu wrote:
> When Xen is built without HAS_PASSTHROUGH, there are some parts
> in arm where iommu_* functions are called in the codebase, but
> their implementation is under xen/drivers/passthrough that is
> not built.
>
> So provide some stub for these functions in order to build Xen
> when !HAS_PASSTHROUGH, which is the case for example on systems
> with MPU support.
>
> For gnttab_need_iommu_mapping() in the Arm part, modify the macro
> to use IS_ENABLED for the HAS_PASSTHROUGH Kconfig.
>
> Fixes: 0388a5979b21 ("xen/arm: mpu: Introduce choice between MMU and MPU")
> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
> ---
> v4 changes:
>   - re-introduced stub for iommu_use_hap_pt, Stefano suggested
>     it is ok to have it in iommu.h.
>   - Reworded comment in iommu_domain_init from Jan suggestion
>
> v3 Changes:
>   - removed stub for iommu_use_hap_pt, another solution will be
>     done for the instance in common arm code.
>   - Moved a comment close to the macro it was referred to
>   - add comment to iommu_domain_init() stub
>   - modified commit message
>   - Add fixes tag
>
> v2 Changes:
>   - modify gnttab_need_iommu_mapping to use IS_ENABLED
>   - removed macro that didn't allow some of the parameter to be
>     evaluated
>   - Changed commit message
> ---
> ---
>   xen/arch/arm/include/asm/grant_table.h |  5 +--
>   xen/include/xen/iommu.h                | 50 +++++++++++++++++++++++++-
>   2 files changed, 52 insertions(+), 3 deletions(-)
>
> diff --git a/xen/arch/arm/include/asm/grant_table.h 
> b/xen/arch/arm/include/asm/grant_table.h
> index d3c518a926b9..c5d87b60c4df 100644
> --- a/xen/arch/arm/include/asm/grant_table.h
> +++ b/xen/arch/arm/include/asm/grant_table.h
> @@ -73,8 +73,9 @@ int replace_grant_host_mapping(uint64_t gpaddr, mfn_t frame,
>   #define gnttab_status_gfn(d, t, i)                                       \
>       page_get_xenheap_gfn(gnttab_status_page(t, i))
>   
> -#define gnttab_need_iommu_mapping(d)                    \
> -    (is_domain_direct_mapped(d) && is_iommu_enabled(d))
> +#define gnttab_need_iommu_mapping(d)                                     \
> +    (IS_ENABLED(CONFIG_HAS_PASSTHROUGH) && is_domain_direct_mapped(d) && \
> +     is_iommu_enabled(d))
>   
>   #endif /* __ASM_GRANT_TABLE_H__ */
>   /*
> diff --git a/xen/include/xen/iommu.h b/xen/include/xen/iommu.h
> index 77a514019cc6..5ac038521e23 100644
> --- a/xen/include/xen/iommu.h
> +++ b/xen/include/xen/iommu.h
> @@ -110,6 +110,8 @@ extern int8_t iommu_hwdom_reserved;
>   
>   extern unsigned int iommu_dev_iotlb_timeout;
>   
> +#ifdef CONFIG_HAS_PASSTHROUGH
> +
>   int iommu_setup(void);
>   int iommu_hardware_setup(void);
>   
> @@ -122,6 +124,28 @@ int arch_iommu_domain_init(struct domain *d);
>   void arch_iommu_check_autotranslated_hwdom(struct domain *d);
>   void arch_iommu_hwdom_init(struct domain *d);
>   
> +#else
> +
> +static inline int iommu_setup(void)
> +{
> +    return -ENODEV;
> +}
> +
> +static inline int iommu_domain_init(struct domain *d, unsigned int opts)
> +{
> +    /*
> +     * Return as the real iommu_domain_init() would: Success when
> +     * !is_iommu_enabled(), following from !iommu_enabled when !HAS_PASSTHROUGH
> +     */
> +    return 0;
> +}
> +
> +static inline void iommu_hwdom_init(struct domain *d) {}
> +
> +static inline void iommu_domain_destroy(struct domain *d) {}
> +
> +#endif /* HAS_PASSTHROUGH */
> +
>   /*
>    * The following flags are passed to map (applicable ones also to unmap)
>    * operations, while some are passed back by lookup operations.
> @@ -209,6 +233,8 @@ struct msi_msg;
>   #ifdef CONFIG_HAS_DEVICE_TREE
>   #include <xen/device_tree.h>
>   
> +#ifdef CONFIG_HAS_PASSTHROUGH
> +
>   int iommu_assign_dt_device(struct domain *d, struct dt_device_node *dev);
>   int iommu_deassign_dt_device(struct domain *d, struct dt_device_node *dev);
>   int iommu_dt_domain_init(struct domain *d);
> @@ -238,6 +264,26 @@ int iommu_do_dt_domctl(struct xen_domctl *domctl, struct 
> domain *d,
>    */
>   int iommu_remove_dt_device(struct dt_device_node *np);
>   
> +#else
> +
> +static inline int iommu_assign_dt_device(struct domain *d,
> +                                         struct dt_device_node *dev)
> +{
> +    return -EINVAL;
> +}
> +
> +static inline int iommu_add_dt_device(struct dt_device_node *np)
> +{
> +    return 1;
I would suggest to add a comment explain what 1 means. IIRC, this means 
"no iommu" present.
Other than that:

Acked-by: Julien Grall <jgrall@xxxxxxxxxx>

Cheers,

--
Julien Grall