Re: [Xen-devel] [PATCH] xen/arm32: setup: Give a xenheap page to the boot allocator

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 17 Sep 2019, Julien Grall wrote:
> After commit 6e3e771203 "xen/arm: setup: Relocate the Device-Tree later on
> in the boot", the boot allocator will not receive any xenheap page (i.e.
> mapped page) on Arm32.
> 
> However, the boot allocator implicitely rely on having the first page
> already mapped and therefore result to break boot on Arm32.
> 
> The easiest way for now is to give a xenheap page to the boot allocator.
> We may want to rethink the interface in the future.
> 
> Fixes: 6e3e771203 ('xen/arm: setup: Relocate the Device-Tree later on in the 
> boot')
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> ---
>  xen/arch/arm/setup.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> index ebbfad94e4..e6ddefb5cf 100644
> --- a/xen/arch/arm/setup.c
> +++ b/xen/arch/arm/setup.c
> @@ -593,6 +593,7 @@ static void __init setup_mm(void)
>      unsigned long heap_pages, xenheap_pages, domheap_pages;
>      int i;
>      const uint32_t ctr = READ_CP32(CTR);
> +    mfn_t boot_mfn_start, boot_mfn_end;
>  
>      if ( !bootinfo.mem.nr_banks )
>          panic("No memory bank\n");
> @@ -665,6 +666,11 @@ static void __init setup_mm(void)
>  
>      setup_xenheap_mappings((e >> PAGE_SHIFT) - xenheap_pages, xenheap_pages);
>  
> +    /* We need a single mapped page for populating bootmem_region_list. */
> +    boot_mfn_start = mfn_add(xenheap_mfn_end, -1);
> +    boot_mfn_end = xenheap_mfn_end;
> +    init_boot_pages(mfn_to_maddr(boot_mfn_start), 
> mfn_to_maddr(boot_mfn_end));
> +
>      /* Add non-xenheap memory */
>      for ( i = 0; i < bootinfo.mem.nr_banks; i++ )
>      {
> @@ -710,7 +716,7 @@ static void __init setup_mm(void)
>  
>      /* Add xenheap memory that was not already added to the boot allocator. 
> */
>      init_xenheap_pages(mfn_to_maddr(xenheap_mfn_start),
> -                       mfn_to_maddr(xenheap_mfn_end));
> +                       mfn_to_maddr(boot_mfn_end));

I can see what you are trying to do with this patch and it looks like
the right fix at the moment. However, shouldn't this last change:

  mfn_to_maddr(boot_mfn_start)


>  }
>  #else /* CONFIG_ARM_64 */
>  static void __init setup_mm(void)


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