Re: [PATCH v5 3/8] xen/arm: allocate static shared memory to a specific owner domain

[Julien Grall <julien@xxxxxxx>]

Hi Penny,

On 20/06/2022 06:11, Penny Zheng wrote:
> If owner property is defined, then owner domain of a static shared memory
> region is not the default dom_io anymore, but a specific domain.
>
> This commit implements allocating static shared memory to a specific domain
> when owner property is defined.
>
> Coding flow for dealing borrower domain will be introduced later in the
> following commits.
>
> Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
> Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> ---
> v5 change:
> - no change
> ---
> v4 change:
> - no changes
> ---
> v3 change:
> - simplify the code since o_gbase is not used if the domain is dom_io
> ---
> v2 change:
> - P2M mapping is restricted to normal domain
> - in-code comment fix
> ---
>   xen/arch/arm/domain_build.c | 44 +++++++++++++++++++++++++++----------
>   1 file changed, 33 insertions(+), 11 deletions(-)
>
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index 91a5ace851..d4fd64e2bd 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -805,9 +805,11 @@ static mfn_t __init acquire_shared_memory_bank(struct 
> domain *d,
>    */
>   static int __init allocate_shared_memory(struct domain *d,
>                                            u32 addr_cells, u32 size_cells,
> -                                         paddr_t pbase, paddr_t psize)
> +                                         paddr_t pbase, paddr_t psize,
> +                                         paddr_t gbase)
>   {
>       mfn_t smfn;
> +    int ret = 0;
>   
>       dprintk(XENLOG_INFO,
>               "Allocate static shared memory BANK %#"PRIpaddr"-%#"PRIpaddr".\n",
> @@ -822,8 +824,18 @@ static int __init allocate_shared_memory(struct domain *d,
>        * DOMID_IO is the domain, like DOMID_XEN, that is not auto-translated.
>        * It sees RAM 1:1 and we do not need to create P2M mapping for it
>        */
> -    ASSERT(d == dom_io);
> -    return 0;
> +    if ( d != dom_io )
> +    {
> +        ret = guest_physmap_add_pages(d, gaddr_to_gfn(gbase), smfn, 
> PFN_DOWN(psize));
Coding style: this line is over 80 characters. And...

> +        if ( ret )
> +        {
> +            printk(XENLOG_ERR
> +                   "Failed to map shared memory to %pd.\n", d);
... this line could be merged with the previous one.

> +            return ret;
> +        }
> +    }
> +
> +    return ret;
>   }
>   
>   static int __init process_shm(struct domain *d,
> @@ -836,6 +848,8 @@ static int __init process_shm(struct domain *d,
>       u32 shm_id;
>       u32 addr_cells, size_cells;
>       paddr_t gbase, pbase, psize;
> +    const char *role_str;
> +    bool owner_dom_io = true;
I think it would be best if role_str and owner_dom_io are defined within 
the loop. Same goes for all the other declarations.
>   
>       dt_for_each_child_node(node, shm_node)
>       {
> @@ -862,19 +876,27 @@ static int __init process_shm(struct domain *d,
>           ASSERT(IS_ALIGNED(pbase, PAGE_SIZE) && IS_ALIGNED(psize, PAGE_SIZE));
>           gbase = dt_read_number(cells, addr_cells);
>   
> -        /* TODO: Consider owner domain is not the default dom_io. */
> +        /*
> +         * "role" property is optional and if it is defined explicitly,
> +         * then the owner domain is not the default "dom_io" domain.
> +         */
> +        if ( dt_property_read_string(shm_node, "role", &role_str) == 0 )
> +            owner_dom_io = false
IIUC, the role is per-region. However, owner_dom_io is first initialized 
to false outside the loop. Therefore, the variable may not be correct on 
the next region.
So I think you want to write:

owner_dom_io = !dt_property_read_string(...);

This can also be avoided if you reduce the scope of the variable (it is 
meant to only be used in the loop).
> +
>           /*
>            * Per static shared memory region could be shared between multiple
>            * domains.
> -         * In case re-allocating the same shared memory region, we check
> -         * if it is already allocated to the default owner dom_io before
> -         * the actual allocation.
> +         * So when owner domain is the default dom_io, in case re-allocating
> +         * the same shared memory region, we check if it is already allocated
> +         * to the default owner dom_io before the actual allocation.
>            */
> -        if ( !is_shm_allocated_to_domio(pbase) )
> +        if ( (owner_dom_io && !is_shm_allocated_to_domio(pbase)) ||
> +             (!owner_dom_io && strcmp(role_str, "owner") == 0) )
>           {
> -            /* Allocate statically shared pages to the default owner dom_io. */
> -            ret = allocate_shared_memory(dom_io, addr_cells, size_cells,
> -                                         pbase, psize);
> +            /* Allocate statically shared pages to the owner domain. */
> +            ret = allocate_shared_memory(owner_dom_io ? dom_io : d,
> +                                         addr_cells, size_cells,
> +                                         pbase, psize, gbase);
>               if ( ret )
>                   return ret;
>           }
Cheers,

--
Julien Grall