Re: [Xen-devel] [RFC 21/29] xen/arm: WORKAROUND 1:1 memory mapping for dom0

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2013-04-29 at 00:02 +0100, Julien Grall wrote:
> Currently xen doesn't implement SYS MMU. When a device will talk with dom0
> with DMA request the domain will use GFN instead of MFN.
> For instance on the arndale board, without this patch the network doesn't
> work.

Yes :-/ Pragmatically I think we are better off with this short term
hack than without support for the Arndale, but it's not terribly
satisfactory. If there were any other platforms available I'd say that
we should pick a platform for which the IOMMU docs were more easily
forthcoming than they have proven to be on this platform.

I'm slightly worried that we may get stuck with this hack. Perhaps we
should say, prominently, that this hack will go away in 4.4 and that
platforms which have not been converted to an IOMMU will not be
supported from 4.4 onwards and that, yes, this could include the arndale
unless docs and/or a vendor written driver appear.

Of course we may end up eating crow if all the other platforms have the
same problem, since we clearly can't remove support for all platforms...

> The 1:1 mapping is a workaround and MUST be remove as soon as a SYS MMU is
> implemented in XEN.

I wonder if we can make this conditional on a suitable board level DT
compat node ("samsung,arndale" or "samsung,exynos5250" perhaps)? And
print a big warning when enabling it of course.

> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> ---
>  xen/arch/arm/domain_build.c |   51 
> ++++++++++++++++++++++++-------------------
>  xen/arch/arm/kernel.h       |    1 -
>  2 files changed, 28 insertions(+), 24 deletions(-)
> 
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index ced73a7..11298e1 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -66,29 +66,36 @@ static int set_memory_reg(struct domain *d, struct 
> kernel_info *kinfo,
>                            int address_cells, int size_cells, u32 *new_cell)
>  {
>      int reg_size = (address_cells + size_cells) * sizeof(*cell);
> -    int l = 0;
> -    u64 start;
> -    u64 size;
> +    paddr_t start;
> +    paddr_t size;
> +    struct page_info *pg;
> +    unsigned int order = get_order_from_bytes(dom0_mem);
> +    int res;
> +    paddr_t spfn;
>  
> -    while ( kinfo->unassigned_mem > 0 && l + reg_size <= len
> -            && kinfo->mem.nr_banks < NR_MEM_BANKS )
> -    {
> -        device_tree_get_reg(&cell, address_cells, size_cells, &start, &size);
> -        if ( size > kinfo->unassigned_mem )
> -            size = kinfo->unassigned_mem;
> -        device_tree_set_reg(&new_cell, address_cells, size_cells, start, 
> size);
> -
> -        printk("Populate P2M %#"PRIx64"->%#"PRIx64"\n", start, start + size);
> -        p2m_populate_ram(d, start, start + size);
> -        kinfo->mem.bank[kinfo->mem.nr_banks].start = start;
> -        kinfo->mem.bank[kinfo->mem.nr_banks].size = size;
> -        kinfo->mem.nr_banks++;
> -        kinfo->unassigned_mem -= size;
> -
> -        l += reg_size;
> -    }
> +    pg = alloc_domheap_pages(d, order, 0);
> +    if ( !pg )
> +        panic("Failed to allocate contiguous memory for dom0\n");

Interesting, so we don't actually need RAM to start at the same place as
the real hardware would have it and the kernel copes? Slight surprising
the kernel didn't whine, but OK!

> +    spfn = page_to_mfn(pg);
> +    start = spfn << PAGE_SHIFT;
> +    size = (1 << order) << PAGE_SHIFT;
> +
> +    // 1:1 mapping
> +    printk("Populate P2M %#"PRIx64"->%#"PRIx64" (1:1 mapping for dom0)\n",
> +           start, start + size);
> +    res = guest_physmap_add_page(d, spfn, spfn, order);
>  
> -    return l;
> +    if ( res )
> +        panic("Unable to add pages in DOM0: %d\n", res);
> +
> +    device_tree_set_reg(&new_cell, address_cells, size_cells, start, size);
> +
> +    kinfo->mem.bank[0].start = start;
> +    kinfo->mem.bank[0].size = size;
> +    kinfo->mem.nr_banks = 1;
> +
> +    return reg_size;
>  }
>  
>  static int write_properties(struct domain *d, struct kernel_info *kinfo,
> @@ -434,8 +441,6 @@ static int prepare_dtb(struct domain *d, struct 
> kernel_info *kinfo)
>      int new_size;
>      int ret;
>  
> -    kinfo->unassigned_mem = dom0_mem;
> -
>      fdt = device_tree_flattened;
>  
>      new_size = fdt_totalsize(fdt) + DOM0_FDT_EXTRA_SIZE;
> diff --git a/xen/arch/arm/kernel.h b/xen/arch/arm/kernel.h
> index 1776a4d..687f6c4 100644
> --- a/xen/arch/arm/kernel.h
> +++ b/xen/arch/arm/kernel.h
> @@ -15,7 +15,6 @@ struct kernel_info {
>  #endif
>  
>      void *fdt; /* flat device tree */
> -    paddr_t unassigned_mem; /* RAM not (yet) assigned to a bank */
>      struct dt_mem_info mem;
>  
>      paddr_t dtb_paddr;



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