Re: [PATCH RFC 21/55] x86_64/mm: introduce pl2e in paging_init

["Nuernberger, Stefan" <snu@amazon.de>]

On Thu, 2019-02-07 at 16:44 +0000, Wei Liu wrote:
> Introduce pl2e so that we can use l2_ro_mpt to point to the page
> table
> itself.
> 
> No functional change.
> 
> Signed-off-by: Wei Liu <wei.liu2@citrix.com>
> ---
>  xen/arch/x86/x86_64/mm.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/xen/arch/x86/x86_64/mm.c b/xen/arch/x86/x86_64/mm.c
> index d8f558bc3a..83d62674c0 100644
> --- a/xen/arch/x86/x86_64/mm.c
> +++ b/xen/arch/x86/x86_64/mm.c
> @@ -497,7 +497,7 @@ void __init paging_init(void)
>      unsigned long i, mpt_size, va;
>      unsigned int n, memflags;
>      l3_pgentry_t *l3_ro_mpt;
> -    l2_pgentry_t *l2_ro_mpt = NULL;
> +    l2_pgentry_t *pl2e = NULL, *l2_ro_mpt;

nit: In the next patch the NULL initialization for l2_ro_mpt is added
back in. No need to remove it here.

>      struct page_info *l1_pg;
>  
>      /*
> @@ -547,7 +547,7 @@ void __init paging_init(void)
>              (L2_PAGETABLE_SHIFT - 3 + PAGE_SHIFT)));
>  
>          if ( cpu_has_page1gb &&
> -             !((unsigned long)l2_ro_mpt & ~PAGE_MASK) &&
> +             !((unsigned long)pl2e & ~PAGE_MASK) &&
>               (mpt_size >> L3_PAGETABLE_SHIFT) > (i >>
> PAGETABLE_ORDER) )
>          {
>              unsigned int k, holes;
> @@ -606,7 +606,7 @@ void __init paging_init(void)
>              memset((void *)(RDWR_MPT_VIRT_START + (i <<
> L2_PAGETABLE_SHIFT)),
>                     0xFF, 1UL << L2_PAGETABLE_SHIFT);
>          }
> -        if ( !((unsigned long)l2_ro_mpt & ~PAGE_MASK) )
> +        if ( !((unsigned long)pl2e & ~PAGE_MASK) )
>          {
>              if ( (l2_ro_mpt = alloc_xen_pagetable()) == NULL )
>                  goto nomem;
> @@ -614,13 +614,14 @@ void __init paging_init(void)
>              l3e_write(&l3_ro_mpt[l3_table_offset(va)],
>                        l3e_from_paddr(__pa(l2_ro_mpt),
>                                       __PAGE_HYPERVISOR_RO |
> _PAGE_USER));
> +            pl2e = l2_ro_mpt;
>              ASSERT(!l2_table_offset(va));
>          }
>          /* NB. Cannot be GLOBAL: guest user mode should not see it.
> */
>          if ( l1_pg )
> -            l2e_write(l2_ro_mpt, l2e_from_page(
> +            l2e_write(pl2e, l2e_from_page(
>                  l1_pg,
> /*_PAGE_GLOBAL|*/_PAGE_PSE|_PAGE_USER|_PAGE_PRESENT));
> -        l2_ro_mpt++;
> +        pl2e++;
>      }
>  #undef CNT
>  #undef MFN
> @@ -636,7 +637,8 @@ void __init paging_init(void)
>      clear_page(l2_ro_mpt);
>      l3e_write(&l3_ro_mpt[l3_table_offset(HIRO_COMPAT_MPT_VIRT_START)
> ],
>                l3e_from_paddr(__pa(l2_ro_mpt),
> __PAGE_HYPERVISOR_RO));
> -    l2_ro_mpt += l2_table_offset(HIRO_COMPAT_MPT_VIRT_START);
> +    pl2e = l2_ro_mpt;
> +    pl2e += l2_table_offset(HIRO_COMPAT_MPT_VIRT_START);

nit: Those two lines could be combined.

- Stefan

>      /* Allocate and map the compatibility mode machine-to-phys
> table. */
>      mpt_size = (mpt_size >> 1) + (1UL << (L2_PAGETABLE_SHIFT - 1));
>      if ( mpt_size > RDWR_COMPAT_MPT_VIRT_END -
> RDWR_COMPAT_MPT_VIRT_START )
> @@ -649,7 +651,7 @@ void __init paging_init(void)
>               sizeof(*compat_machine_to_phys_mapping))
>      BUILD_BUG_ON((sizeof(*frame_table) & ~sizeof(*frame_table)) % \
>                   sizeof(*compat_machine_to_phys_mapping));
> -    for ( i = 0; i < (mpt_size >> L2_PAGETABLE_SHIFT); i++,
> l2_ro_mpt++ )
> +    for ( i = 0; i < (mpt_size >> L2_PAGETABLE_SHIFT); i++, pl2e++ )
>      {
>          memflags = MEMF_node(phys_to_nid(i <<
>              (L2_PAGETABLE_SHIFT - 2 + PAGE_SHIFT)));
> @@ -671,7 +673,7 @@ void __init paging_init(void)
>                 0x55,
>                 1UL << L2_PAGETABLE_SHIFT);
>          /* NB. Cannot be GLOBAL as the ptes get copied into per-VM
> space. */
> -        l2e_write(l2_ro_mpt, l2e_from_page(l1_pg,
> _PAGE_PSE|_PAGE_PRESENT));
> +        l2e_write(pl2e, l2e_from_page(l1_pg,
> _PAGE_PSE|_PAGE_PRESENT));
>      }
>  #undef CNT
>  #undef MFN



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