Re: [Xen-devel] [PATCH 06/11] ARM: simplify page type handling

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 21 Jun 2017, Jan Beulich wrote:
> There's no need to have anything here on ARM other than the distinction
> between writable and non-writable pages (and even that could likely be
> eliminated, but with a more intrusive change). Limit type to a single
> bit and drop pinned and validated flags altogether.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
> Note: Compile tested only.
> 
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -1113,8 +1113,7 @@ void share_xen_page_with_guest(struct pa
>      spin_lock(&d->page_alloc_lock);
>  
>      /* The incremented type count pins as writable or read-only. */
> -    page->u.inuse.type_info  = (readonly ? PGT_none : PGT_writable_page);
> -    page->u.inuse.type_info |= PGT_validated | 1;
> +    page->u.inuse.type_info = (readonly ? PGT_none : PGT_writable_page) | 1;
>  
>      page_set_owner(page, d);
>      smp_wmb(); /* install valid domain ptr before updating refcnt. */
> --- a/xen/common/memory.c
> +++ b/xen/common/memory.c
> @@ -354,8 +354,10 @@ int guest_remove_page(struct domain *d,
>  
>      rc = guest_physmap_remove_page(d, _gfn(gmfn), mfn, 0);
>  
> +#ifdef _PGT_pinned
>      if ( !rc && test_and_clear_bit(_PGT_pinned, &page->u.inuse.type_info) )
>          put_page_and_type(page);
> +#endif
>  
>      /*
>       * With the lack of an IOMMU on some platforms, domains with DMA-capable
> --- a/xen/include/asm-arm/mm.h
> +++ b/xen/include/asm-arm/mm.h
> @@ -77,20 +77,12 @@ struct page_info
>  #define PG_shift(idx)   (BITS_PER_LONG - (idx))
>  #define PG_mask(x, idx) (x ## UL << PG_shift(idx))
>  
> -#define PGT_none          PG_mask(0, 4)  /* no special uses of this page   */
> -#define PGT_writable_page PG_mask(7, 4)  /* has writable mappings?         */
> -#define PGT_type_mask     PG_mask(15, 4) /* Bits 28-31 or 60-63.           */
> -
> - /* Owning guest has pinned this page to its current type? */
> -#define _PGT_pinned       PG_shift(5)
> -#define PGT_pinned        PG_mask(1, 5)
> -
> - /* Has this page been validated for use as its current type? */
> -#define _PGT_validated    PG_shift(6)
> -#define PGT_validated     PG_mask(1, 6)
> +#define PGT_none          PG_mask(0, 1)  /* no special uses of this page   */
> +#define PGT_writable_page PG_mask(1, 1)  /* has writable mappings?         */
> +#define PGT_type_mask     PG_mask(1, 1)  /* Bits 31 or 63.                 */
>  
>   /* Count of uses of this frame as its current type. */
> -#define PGT_count_width   PG_shift(9)
> +#define PGT_count_width   PG_shift(2)
>  #define PGT_count_mask    ((1UL<<PGT_count_width)-1)
>  
>   /* Cleared when the owning guest 'frees' this page. */
> 
> 
> 
> 

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