Re: [PATCH v3 35/52] xen/arm: map static memory on demand

[Ayan Kumar Halder <ayankuma@xxxxxxx>]

Hi Penny,

On 26/06/2023 04:34, Penny Zheng wrote:
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>
>
> In function init_staticmem_pages, we need the access to static memory
> for proper initialization.
> It is not a problem in MMU system, as Xen map the whole RAM in
> setup_mm(). However, with limited MPU memory regions, it is too luxury
> to map the whole RAM.
> As a result, we follow the rule of "map on demand", to map static memory
> temporarily before its initialization, and unmap immediately after its
> initialization.
I could see that you are using _PAGE_TRANSIENT  to map memory 
temporarily. However, I don't see this being translated to any of the 
MPU hardware features (ie _PAGE_TRANSIENT does not seem to translate to 
any of the attributes in PRBAR, PRLAR, PRENR, etc). Thus, how is it 
different from mapping the memory in "non temporary" way ?
Please let me know what I am missing.

- Ayan

> Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
> Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> ---
> v3:
> - new commit
> ---
>   xen/arch/arm/include/asm/mm.h |  2 ++
>   xen/arch/arm/mmu/mm.c         | 10 ++++++++++
>   xen/arch/arm/mpu/mm.c         | 10 ++++++++++
>   xen/arch/arm/setup.c          | 21 +++++++++++++++++++++
>   4 files changed, 43 insertions(+)
>
> diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h
> index 66d98b9a29..cffbf8a595 100644
> --- a/xen/arch/arm/include/asm/mm.h
> +++ b/xen/arch/arm/include/asm/mm.h
> @@ -224,6 +224,8 @@ extern void mm_init_secondary_cpu(void);
>   extern void setup_frametable_mappings(paddr_t ps, paddr_t pe);
>   /* map a physical range in virtual memory */
>   void __iomem *ioremap_attr(paddr_t start, size_t len, unsigned int 
> attributes);
> +extern int map_staticmem_pages_to_xen(paddr_t start, paddr_t end);
> +extern int unmap_staticmem_pages_to_xen(paddr_t start, paddr_t end);
>
>   static inline void __iomem *ioremap_nocache(paddr_t start, size_t len)
>   {
> diff --git a/xen/arch/arm/mmu/mm.c b/xen/arch/arm/mmu/mm.c
> index 2f29cb53fe..4196a55c32 100644
> --- a/xen/arch/arm/mmu/mm.c
> +++ b/xen/arch/arm/mmu/mm.c
> @@ -1113,6 +1113,16 @@ int populate_pt_range(unsigned long virt, unsigned long 
> nr_mfns)
>       return xen_pt_update(virt, INVALID_MFN, nr_mfns, _PAGE_POPULATE);
>   }
>
> +int __init map_staticmem_pages_to_xen(paddr_t start, paddr_t end)
> +{
> +    return 0;
> +}
> +
> +int __init unmap_staticmem_pages_to_xen(paddr_t start, paddr_t end)
> +{
> +    return 0;
> +}
> +
>   /*
>    * Local variables:
>    * mode: C
> diff --git a/xen/arch/arm/mpu/mm.c b/xen/arch/arm/mpu/mm.c
> index a40055ae5e..9d5c1da39c 100644
> --- a/xen/arch/arm/mpu/mm.c
> +++ b/xen/arch/arm/mpu/mm.c
> @@ -614,6 +614,16 @@ void __init setup_frametable_mappings(paddr_t ps, paddr_t 
> pe)
>              frametable_size - (nr_pdxs * sizeof(struct page_info)));
>   }
>
> +int __init map_staticmem_pages_to_xen(paddr_t start, paddr_t end)
> +{
> +    return xen_mpumap_update(start, end, PAGE_HYPERVISOR | _PAGE_TRANSIENT);
> +}
> +
> +int __init unmap_staticmem_pages_to_xen(paddr_t start, paddr_t end)
> +{
> +    return xen_mpumap_update(start, end, 0);
> +}
> +
>   /*
>    * Local variables:
>    * mode: C
> diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> index f42b53d17b..c21d1db763 100644
> --- a/xen/arch/arm/setup.c
> +++ b/xen/arch/arm/setup.c
> @@ -637,12 +637,33 @@ void __init init_staticmem_pages(void)
>               mfn_t bank_start = 
> _mfn(PFN_UP(bootinfo.reserved_mem.bank[bank].start));
>               unsigned long bank_pages = 
> PFN_DOWN(bootinfo.reserved_mem.bank[bank].size);
>               mfn_t bank_end = mfn_add(bank_start, bank_pages);
> +            int res;
>
>               if ( mfn_x(bank_end) <= mfn_x(bank_start) )
>                   return;
>
> +            /* Map temporarily before initialization */
> +            res = map_staticmem_pages_to_xen(mfn_to_maddr(bank_start),
> +                                             mfn_to_maddr(bank_end));
> +            if ( res )
> +            {
> +                printk(XENLOG_ERR "Failed to map static memory to Xen: %d\n",
> +                       res);
> +                return;
> +            }
> +
>               unprepare_staticmem_pages(mfn_to_page(bank_start),
>                                         bank_pages, false);
> +
> +            /* Unmap immediately after initialization */
> +            res = unmap_staticmem_pages_to_xen(mfn_to_maddr(bank_start),
> +                                               mfn_to_maddr(bank_end));
> +            if ( res )
> +            {
> +                printk(XENLOG_ERR "Failed to unmap static memory to Xen: %d\n",
> +                       res);
> +                return;
> +            }
>           }
>       }
>   #endif
> --
> 2.25.1