Re: [Qemu-devel] [PATCH 09/11] PPC64: Fix NX bit

[Hollis Blanchard]

On Fri, 2009-03-06 at 16:36 +0100, Alexander Graf wrote:
> This patch fixes two issues with the NX bit:
> 
> 1) The guarded bit has nothing to do with NX.

It turns out that instruction access is not allowed from mappings that
have either N *or* G bits set. (There are also N bits in the segment
entry; not sure how/if those are handled in this path.)

> 2) ctx->nx only got ORed, but never reset. So when one page in the
>    lifetime of the VM was ever NX, all later pages were too.
> 
> Signed-off-by: Alexander Graf <address@hidden>
> ---
>  target-ppc/helper.c |    3 +--
>  1 files changed, 1 insertions(+), 2 deletions(-)
> 
> diff --git a/target-ppc/helper.c b/target-ppc/helper.c
> index 7fe3f8f..58b7fe2 100644
> --- a/target-ppc/helper.c
> +++ b/target-ppc/helper.c
> @@ -226,8 +226,7 @@ static always_inline int _pte_check (mmu_ctx_t *ctx, int 
> is_64b,
>              ptem = pte0 & PTE64_PTEM_MASK;
>              mmask = PTE64_CHECK_MASK;
>              pp = (pte1 & 0x00000003) | ((pte1 >> 61) & 0x00000004);
> -            ctx->nx |= (pte1 >> 2) & 1; /* No execute bit */
> -            ctx->nx |= (pte1 >> 3) & 1; /* Guarded bit    */
> +            ctx->nx = (pte1 >> 2) & 1; /* No execute bit */
>          } else
>  #endif
>          {

-- 
Hollis Blanchard
IBM Linux Technology Center