Re: [PATCH v3 12/19] xen/arm: mm: Allow page-table allocation from the boot allocator

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 21 Feb 2022, Julien Grall wrote:
> From: Julien Grall <julien.grall@xxxxxxx>
> 
> At the moment, page-table can only be allocated from domheap. This means
> it is not possible to create mapping in the page-tables via
> map_pages_to_xen() if page-table needs to be allocated.
> 
> In order to avoid open-coding page-tables update in early boot, we need
> to be able to allocate page-tables much earlier. Thankfully, we have the
> boot allocator for those cases.
> 
> create_xen_table() is updated to cater early boot allocation by using
> alloc_boot_pages().
> 
> Note, this is not sufficient to bootstrap the page-tables (i.e mapping
> before any memory is actually mapped). This will be addressed
> separately.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
>     Changes in v2:
>         - New patch
> ---
>  xen/arch/arm/mm.c | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index 58364bb6c820..f70b8cc7ce87 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -1014,19 +1014,27 @@ static void xen_unmap_table(const lpae_t *table)
>  
>  static int create_xen_table(lpae_t *entry)
>  {
> -    struct page_info *pg;
> +    mfn_t mfn;
>      void *p;
>      lpae_t pte;
>  
> -    pg = alloc_domheap_page(NULL, 0);
> -    if ( pg == NULL )
> -        return -ENOMEM;
> +    if ( system_state != SYS_STATE_early_boot )
> +    {
> +        struct page_info *pg = alloc_domheap_page(NULL, 0);
> +
> +        if ( pg == NULL )
> +            return -ENOMEM;
> +
> +        mfn = page_to_mfn(pg);
> +    }
> +    else
> +        mfn = alloc_boot_pages(1, 1);
>  
> -    p = xen_map_table(page_to_mfn(pg));
> +    p = xen_map_table(mfn);
>      clear_page(p);
>      xen_unmap_table(p);
>  
> -    pte = mfn_to_xen_entry(page_to_mfn(pg), MT_NORMAL);
> +    pte = mfn_to_xen_entry(mfn, MT_NORMAL);
>      pte.pt.table = 1;
>      write_pte(entry, pte);