Re: [Minios-devel] [UNIKRAFT PATCH 17/22] plat/kvm: arm64: Calculate pagetable size dynamically by image size

[Julien Grall <julien.grall@xxxxxxx>]

On 11/8/18 9:51 AM, Wei Chen wrote:
> The previous L3 page table size is a fixed value based on the
> assumption that, image size will not exceed 2MB. But that's not
> true, some applications like node.js will be about 40MB after
> converting to Unikernel. So in this patch, we calculate the
> page table size by real image size. In order to mapping the
> image occupied memory to L3 page table, we round up the image
> size with 2MB.
I am a bit confused, you speak about L3 page-table, but as you round up 
to 2MB, why don't you map using 2MB superpage?
> Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> ---
>   plat/kvm/arm/entry64.S              | 33 +++++++++++++++++++++++++++--
>   plat/kvm/arm/pagetable64.S          |  7 ++++--
>   plat/kvm/arm/setup.c                |  2 +-
>   plat/kvm/include/kvm-arm/arm64/mm.h | 14 ++++++------
>   4 files changed, 45 insertions(+), 11 deletions(-)
>
> diff --git a/plat/kvm/arm/entry64.S b/plat/kvm/arm/entry64.S
> index c1af0a4..72e170f 100644
> --- a/plat/kvm/arm/entry64.S
> +++ b/plat/kvm/arm/entry64.S
> @@ -36,6 +36,11 @@
>   #include <kvm-arm/mm.h>
>   #include <arm/cpu_defs.h>
>   
> +.global page_table_size
> +.data
> +page_table_size:
> +    .dword 0x0
> +
>   /*
>    * The registers used by _libkvmplat_start:
>    * x0 - FDT pointer
> @@ -60,9 +65,29 @@ ENTRY(_libkvmplat_entry)
>         msr sctlr_el1, x2
>         isb
>   
> -	/* Boot stack is placed after pagetable area temporarily */
> +       /* Caculate the image size */
>         ldr x26, =_end
> -       add x26, x26, #PAGE_TABLE_SIZE
> +       ldr x15, =_dtb
> +       sub x15, x26, x15
> +
> +       /* Round up the size to 2MB */
> +       mov x17, #0xfffff
> +       add x15, x15, x17
> +       and x15, x15, #0xfffffffffff00000
Please use macros for the both values. But this could be simplified 
using lsr, lsl here.
> +
> +       /*
> +        * How many bytes would be used for L3_TABLE
> +        * ((x15 >> 21) << 12)
> +        */
> +       lsr x17, x15, #9
> +
> +       /* Total bytes for pagetable */
> +       add x17, x17, #L0_TABLE_SIZE
> +       add x17, x17, #L1_TABLE_SIZE
> +       add x17, x17, #L2_TABLE_SIZE
> +
> +       /* Boot stack is placed after pagetable area temporarily */
> +       add x26, x26, x17
>         add x27, x26, #__STACK_SIZE
>   
>   	/*
> @@ -84,6 +109,10 @@ ENTRY(_libkvmplat_entry)
>         /* Set the context id */
>         msr contextidr_el1, xzr
>   
> +	/* Save page table size for later usage */
> +       ldr x26, =page_table_size
> +       str x17, [x26]
> +
>         /* Create a pagetable to do PA == VA mapping */
>         bl create_pagetables
>   
> diff --git a/plat/kvm/arm/pagetable64.S b/plat/kvm/arm/pagetable64.S
> index cf30584..7d19f6b 100644
> --- a/plat/kvm/arm/pagetable64.S
> +++ b/plat/kvm/arm/pagetable64.S
> @@ -72,7 +72,8 @@ ENTRY(create_pagetables)
>   
>   	/* Clean the page table */
>         mov x6, x14
> -       add x13, x14, #PAGE_TABLE_SIZE
> +       ldr x13, =page_table_size
> +       ldr x13, [x13]
>   1:
>         stp  xzr, xzr, [x6], #16
>         stp  xzr, xzr, [x6], #16
> @@ -244,7 +245,9 @@ ENTRY(start_mmu)
>          */
>         ldr x0, =_data
>         ldr x1, =_end
> -       add x1, x1, #PAGE_TABLE_SIZE
> +       ldr x2, =page_table_size
> +       ldr x2, [x2]
> +       add x1, x2, x1
>         add x1, x1, #__STACK_SIZE
>         sub x1, x1, x0
>         bl clean_and_invalidate_dcache_range
> diff --git a/plat/kvm/arm/setup.c b/plat/kvm/arm/setup.c
> index 59faaa2..bfbb627 100644
> --- a/plat/kvm/arm/setup.c
> +++ b/plat/kvm/arm/setup.c
> @@ -147,7 +147,7 @@ static void _init_dtb_mem(void)
>   
>   	max_addr = mem_base + mem_size;
>         _libkvmplat_pagetable =(void *) ALIGN_DOWN((size_t)&_end, __PAGE_SIZE);
> -       _libkvmplat_heap_start = _libkvmplat_pagetable + PAGE_TABLE_SIZE;
> +       _libkvmplat_heap_start = _libkvmplat_pagetable + page_table_size;
>         _libkvmplat_mem_end = (void *) max_addr;
>   
>   	/* AArch64 require stack be 16-bytes alignment by default */
> diff --git a/plat/kvm/include/kvm-arm/arm64/mm.h 
> b/plat/kvm/include/kvm-arm/arm64/mm.h
> index 23bc658..9ec1273 100644
> --- a/plat/kvm/include/kvm-arm/arm64/mm.h
> +++ b/plat/kvm/include/kvm-arm/arm64/mm.h
> @@ -69,15 +69,17 @@
>   #define L2_TABLE_SIZE   __PAGE_SIZE
>   
>   /*
> - * As Unikraft image's size is very tiny, from tens to hundreds kilo
> - * bytes. So one page for L3_TABLE is enough for us to manage section
> - * attributes of image.
> + * We will use Unikraft image's size to caculate the L3_TABLE_SIZE.
> + * Because we allocate one page for L2 TABLE, fo the max image size
> + * would be 1GB. It would be enough for current stage.
>    */
>   #define L3_TABLE_OFFSET (L2_TABLE_OFFSET + L2_TABLE_SIZE)
> -#define L3_TABLE_SIZE   __PAGE_SIZE
> +
> +#ifndef __ASSEMBLY__
>   
>   /* Total memory size that will be used by pagetable */
> -#define PAGE_TABLE_SIZE (L0_TABLE_SIZE + L1_TABLE_SIZE + \
> -                               L2_TABLE_SIZE + L3_TABLE_SIZE)
> +extern uint64_t page_table_size;
> +
> +#endif /*__ASSEMBLY__ */
>   
>   #endif /* __KVM_ARM_64_MM_H__ */
Cheers,

--
Julien Grall

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