Re: [PATCH 1/8] x86/mm: Avoid hard-coding PAT in get_page_from_l1e()

[Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>]

On 06/12/2022 04:33, Demi Marie Obenour wrote:
> This still hard-codes the assumption that the two spare values are
> mapped to UC.  Removing this assumption would require a more complex
> patch.
>
> Signed-off-by: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>

Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

> ---
>  xen/arch/x86/mm.c | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
>
> diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
> index 
> 78b1972e4170cacccc9c37c6e64e76e66a7da87f..5d05399c3a841bf03991a3bed63df9a815c1e891
>  100644
> --- a/xen/arch/x86/mm.c
> +++ b/xen/arch/x86/mm.c
> @@ -961,13 +961,10 @@ get_page_from_l1e(
>  

As you noted that this desperately needs a comment, how about

/* Force cacheable memtypes to UC, */

here?  Can fix up on commit.

~Andrew

>          switch ( l1f & PAGE_CACHE_ATTRS )
>          {
> -        case 0: /* WB */
> -            flip |= _PAGE_PWT | _PAGE_PCD;
> -            break;
> -        case _PAGE_PWT: /* WT */
> -        case _PAGE_PWT | _PAGE_PAT: /* WP */
> -            flip |= _PAGE_PCD | (l1f & _PAGE_PAT);
> -            break;
> +        case _PAGE_WB:
> +        case _PAGE_WT:
> +        case _PAGE_WP:
> +            flip |= (l1f & PAGE_CACHE_ATTRS) ^ _PAGE_UC;
>          }
>  
>          return flip;