Re: [Xen-devel] [PATCH v3] xen/arm: Fix crash if last memory section is bigger than 1gb

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2014-10-02 at 16:16 +0100, Frediano Ziglio wrote:
> setup_xenheap_mappings setup head memory on Arm 32 has a limit of 1gb.
> On system with large memory is possible that there are no blocks of memory
> smaller than 1gb leading xenheap_pages to be more than 1gb.
> This cause memory errors trying to access heap after the 1gb limit.

As I mentioned in a previous round of review this explanation doesn't
really fit.

I think better would be:

        On arm32 the xenheap has a maximum size of 1GB. On systems with
        more than 8GB (so 1/8 total RAM is greater than 1GB) there is no
        point in searching for a region with 1/8 of the total RAM when
        only 1GB will be used. Therefore limit the maximum size to 1GB
        before searching.

If you agree I will make this change upon commit.

> 
> Signed-off-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxxx>
> Reviewed-by: Julien Grall <julien.grall@xxxxxxxxxx>
> ---
>  xen/arch/arm/setup.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> index 446de8a..c43c776 100644
> --- a/xen/arch/arm/setup.c
> +++ b/xen/arch/arm/setup.c
> @@ -500,7 +500,7 @@ static void __init setup_mm(unsigned long
> dtb_paddr, size_t dtb_size)
>       *
>       *  - must be 32 MiB aligned
>       *  - must not include Xen itself or the boot modules
> -     *  - must be at most 1/8 the total RAM in the system
> +     *  - must be at most 1GB or 1/8 the total RAM in the system if less
>       *  - must be at least 128M
>       *
>       * We try to allocate the largest xenheap possible within these
> @@ -509,6 +509,7 @@ static void __init setup_mm(unsigned long
> dtb_paddr, size_t dtb_size)
>      heap_pages = ram_pages;
>      xenheap_pages = (heap_pages/8 + 0x1fffUL) & ~0x1fffUL;
>      xenheap_pages = max(xenheap_pages, 128UL<<(20-PAGE_SHIFT));
> +    xenheap_pages = min(xenheap_pages, 1UL<<(30-PAGE_SHIFT));
> 
>      do
>      {



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