Re: [PATCH v6] xen/arm: Check for Static Heap feature when freeing resources

[Michal Orzel <michal.orzel@xxxxxxx>]

On 12/12/2024 10:30, Luca Fancellu wrote:
> 
> 
> From: Penny Zheng <Penny.Zheng@xxxxxxx>
> 
> If the Xen heap is statically configured in Device Tree, its size is
> definite, so only the defined memory shall be given to the boot
> allocator. Have a check where init_domheap_pages() is called
> which takes into account if static heap feature is used.
> 
> Extract static_heap flag from init data bootinfo, as it will be needed
> after destroying the init data section, rename it to using_static_heap
> and use it to tell whether the Xen static heap feature is enabled.
> 
> Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
> Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
> ---
> Changes from v5:
>  - Drop Jan R-by due to the code changes
>  - Static heap is not dependent on static memory, so delete #ifdefs
>    for CONFIG_STATIC_MEMORY
> Changes from v4:
>  - Add R-by Jan
>  - Changed code to reduce nesting in discard_initial_modules (Julien)
> Changes from v3:
>  - Removed helper using_static_heap(), renamed static_heap variable
>    to using_static_heap and simplified #ifdef-ary (Jan suggestion)
> Changes from v2:
>  - Change xen_is_using_staticheap() to using_static_heap()
>  - Move declaration of static_heap to xen/mm.h and import that in
>    bootfdt.h
>  - Reprased first part of the commit message
> Changes from v1:
>  - moved static_heap to common/page_alloc.c
>  - protect static_heap access with CONFIG_STATIC_MEMORY
>  - update comment in arm/kernel.c kernel_decompress()
> ---
> ---
>  xen/arch/arm/arm32/mmu/mm.c       | 4 ++--
>  xen/arch/arm/kernel.c             | 7 ++++---
>  xen/arch/arm/mmu/setup.c          | 8 ++++++--
>  xen/arch/arm/setup.c              | 3 +++
>  xen/common/device-tree/bootfdt.c  | 2 +-
>  xen/common/device-tree/bootinfo.c | 2 +-
>  xen/common/page_alloc.c           | 3 +++
>  xen/include/xen/bootfdt.h         | 1 -
>  xen/include/xen/mm.h              | 2 ++
>  9 files changed, 22 insertions(+), 10 deletions(-)
> 
> diff --git a/xen/arch/arm/arm32/mmu/mm.c b/xen/arch/arm/arm32/mmu/mm.c
> index 063611412be0..0824d61323b5 100644
> --- a/xen/arch/arm/arm32/mmu/mm.c
> +++ b/xen/arch/arm/arm32/mmu/mm.c
> @@ -199,7 +199,7 @@ void __init setup_mm(void)
> 
>      total_pages = ram_size >> PAGE_SHIFT;
> 
> -    if ( bootinfo.static_heap )
> +    if ( using_static_heap )
>      {
>          const struct membanks *reserved_mem = bootinfo_get_reserved_mem();
> 
> @@ -246,7 +246,7 @@ void __init setup_mm(void)
> 
>      do
>      {
> -        e = bootinfo.static_heap ?
> +        e = using_static_heap ?
>              fit_xenheap_in_static_heap(pfn_to_paddr(xenheap_pages), MB(32)) :
>              consider_modules(ram_start, ram_end,
>                               pfn_to_paddr(xenheap_pages),
> diff --git a/xen/arch/arm/kernel.c b/xen/arch/arm/kernel.c
> index 293d7efaed9c..8270684246ea 100644
> --- a/xen/arch/arm/kernel.c
> +++ b/xen/arch/arm/kernel.c
> @@ -244,10 +244,11 @@ static __init int kernel_decompress(struct bootmodule 
> *mod, uint32_t offset)
>      size += offset;
> 
>      /*
> -     * Free the original kernel, update the pointers to the
> -     * decompressed kernel
> +     * In case Xen is not using the static heap feature, free the original
> +     * kernel, update the pointers to the decompressed kernel
>       */
> -    fw_unreserved_regions(addr, addr + size, init_domheap_pages, 0);
> +    if ( !using_static_heap )
You should get out of this function even earlier, before calculating addr and 
size that are only
used in fw_unreserved_regions.

> +        fw_unreserved_regions(addr, addr + size, init_domheap_pages, 0);
> 
>      return 0;
>  }
> diff --git a/xen/arch/arm/mmu/setup.c b/xen/arch/arm/mmu/setup.c
> index 9664e85ee6c0..8c87649bc88e 100644
> --- a/xen/arch/arm/mmu/setup.c
> +++ b/xen/arch/arm/mmu/setup.c
> @@ -341,8 +341,12 @@ void free_init_memory(void)
>      if ( rc )
>          panic("Unable to remove the init section (rc = %d)\n", rc);
> 
> -    init_domheap_pages(pa, pa + len);
> -    printk("Freed %ldkB init memory.\n", 
> (long)(__init_end-__init_begin)>>10);
> +    if ( !using_static_heap )
So here, you allow the init region mappings to be destroyed (above), yet ...

> +    {
> +        init_domheap_pages(pa, pa + len);
> +        printk("Freed %ldkB init memory.\n",
> +               (long)(__init_end-__init_begin) >> 10);
> +    }
>  }
> 
>  /**
> diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> index 2e27af4560a5..85f743a2c6ad 100644
> --- a/xen/arch/arm/setup.c
> +++ b/xen/arch/arm/setup.c
> @@ -206,6 +206,9 @@ void __init discard_initial_modules(void)
>      struct bootmodules *mi = &bootinfo.modules;
>      int i;
> 
> +    if ( using_static_heap )
> +        return;
... here you would get out without calling remove_early_mappings() that today 
destroys early FDT
mappings. IMO you should allow to call remove_early_mappings().

With the remarks addressed:
Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>

~Michal