Re: [Xen-devel] [PATCH v2 09/10] xen/arm: map reserved-memory regions as normal memory in dom0

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 4/30/19 10:02 PM, Stefano Stabellini wrote:
> reserved-memory regions should be mapped as normal memory. At the
> moment, they get remapped as device memory in dom0 because Xen doesn't
> know any better. Add an explicit check for it.
This part matches the title of the patch but...

> reserved-memory regions overlap with memory nodes. The overlapping
> memory is reserved-memory and should be handled accordingly:
> consider_modules and dt_unreserved_regions should skip these regions the
> same way they are already skipping mem-reserve regions.
... this doesn't. They are actually two different things and should be 
handled in separate patches.
> Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
> ---
> Changes in v2:
> - fix commit message: full overlap
> - remove check_reserved_memory
> - extend consider_modules and dt_unreserved_regions
> ---
>   xen/arch/arm/domain_build.c |  7 +++++++
>   xen/arch/arm/setup.c        | 36 +++++++++++++++++++++++++++++++++---
>   2 files changed, 40 insertions(+), 3 deletions(-)
>
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index 5e7f94c..e5d488d 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -1408,6 +1408,13 @@ static int __init handle_node(struct domain *d, struct 
> kernel_info *kinfo,
>                  "WARNING: Path %s is reserved, skip the node as we may re-use the 
> path.\n",
>                  path);
>   
> +    /*
> +     * reserved-memory ranges should be mapped as normal memory in the
> +     * p2m.
> +     */
> +    if ( !strcmp(dt_node_name(node), "reserved-memory") )
> +        p2mt = p2m_mmio_direct_c;
Do we really need this? The default type is already p2m_mmio_direct_c 
(see default_p2mt).
> +
>       res = handle_device(d, node, p2mt);
>       if ( res)
>           return res;
> diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> index ccb0f18..908b52c 100644
> --- a/xen/arch/arm/setup.c
> +++ b/xen/arch/arm/setup.c
> @@ -204,6 +204,19 @@ void __init dt_unreserved_regions(paddr_t s, paddr_t e,
>           }
>       }
>   
> +    for ( ; i - nr < bootinfo.reserved_mem.nr_banks; i++ )
It took me a bit of time to understand why you do i - nr. I think we 
need some comments explaining the new logic.
Longer term (i.e I will not push for it today :)), I think this code 
would benefits of using e820-like. It would make the code clearer and 
probably more efficient than what we currently have.
> +    {
> +        paddr_t r_s = bootinfo.reserved_mem.bank[i - nr].start;
> +        paddr_t r_e = r_s + bootinfo.reserved_mem.bank[i - nr].size;
> +
> +        if ( s < r_e && r_s < e )
> +        {
> +            dt_unreserved_regions(r_e, e, cb, i+1);
> +            dt_unreserved_regions(s, r_s, cb, i+1);
> +            return;
> +        }
> +    }
> +
>       cb(s, e);
>   }
>   
> @@ -390,7 +403,7 @@ static paddr_t __init consider_modules(paddr_t s, paddr_t e,
>   {
>       const struct bootmodules *mi = &bootinfo.modules;
>       int i;
> -    int nr_rsvd;
> +    int nr;
>   
>       s = (s+align-1) & ~(align-1);
>       e = e & ~(align-1);
> @@ -416,9 +429,9 @@ static paddr_t __init consider_modules(paddr_t s, paddr_t e,
>   
>       /* Now check any fdt reserved areas. */
>   
> -    nr_rsvd = fdt_num_mem_rsv(device_tree_flattened);
> +    nr = fdt_num_mem_rsv(device_tree_flattened);
>   
> -    for ( ; i < mi->nr_mods + nr_rsvd; i++ )
> +    for ( ; i < mi->nr_mods + nr; i++ )
>       {
>           paddr_t mod_s, mod_e;
>   
> @@ -440,6 +453,23 @@ static paddr_t __init consider_modules(paddr_t s, paddr_t e,
>               return consider_modules(s, mod_s, size, align, i+1);
>           }
>       }
> +
> +    /* Now check for reserved-memory regions */
> +    nr += mi->nr_mods;
Similar to the previous function, this needs to be documented.

> +    for ( ; i - nr < bootinfo.reserved_mem.nr_banks; i++ )
> +    {
> +        paddr_t r_s = bootinfo.reserved_mem.bank[i - nr].start;
> +        paddr_t r_e = r_s + bootinfo.reserved_mem.bank[i - nr].size;
> +
> +        if ( s < r_e && r_s < e )
> +        {
> +            r_e = consider_modules(r_e, e, size, align, i+1);
Coding style: space before and after the operator. Ideally, the rest of 
the function should be fixed.
> +            if ( r_e )
> +                return r_e;
> +
> +            return consider_modules(s, r_s, size, align, i+1);
Same here.

> +        }
> +    }
>       return e;
>   }
>   #endif
Cheers,

--
Julien Grall

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