>>> On 18.10.17 at 12:51, <george.dun...@citrix.com> wrote:
> --- a/xen/arch/x86/Kconfig
> +++ b/xen/arch/x86/Kconfig
> @@ -37,6 +37,26 @@ source "arch/Kconfig"
> config PV
> def_bool y
>
> +config PV_LINEAR_PT
> + bool "Support for PV linear pagetables"
> + depends on PV
> + default y
> + ---help---
> + Linear pagetables (also called "recursive pagetables") refers
> + to the practice of a guest operating system having pagetable
> + entries pointing to other pagetables of the same level (i.e.,
> + allowing L2 PTEs to point to other L2 pages). Some operating
> + systems use it as a simple way to consisently map the current
> + process's pagetables into its own virtual address space.
> +
> + Linux and MiniOS don't use this technique. NetBSD and Novell
> + Netware do; there may be other custom operating systems which
> + do. If you're certain you don't plan on having PV guests
> + which use this feature, turning it off can reduce the attack
> + surface.
> +
> + If unsure, say Y.
> +
> config HVM
> def_bool y
Note how the options in context use tab indentation. Granted
there are other examples of space indentation in this file, but
at least they're using 8 spaces (except of course of the help
text), while you're using 7.
> @@ -2320,6 +2353,7 @@ static int _put_page_type(struct page_info *page, bool
> preemptible,
> break;
> }
>
> +#ifdef CONFIG_PV_LINEAR_PT
> if ( ptpg && PGT_type_equal(x, ptpg->u.inuse.type_info) )
> {
> /*
> @@ -2334,6 +2368,9 @@ static int _put_page_type(struct page_info *page, bool
> preemptible,
> ASSERT(ptpg->linear_pt_count > 0);
> ptpg = NULL;
> }
> +#else /* CONFIG_PV_LINEAR_PT */
> + BUG_ON(ptpg && PGT_type_equal(x, ptpg->u.inuse.type_info));
> +#endif
Along the lines of my most recent reply to v1 (which I realize I
did send only after v2 had arrived), I'm not really certain about
the usefulness of the preprocessor conditionals - I'd prefer if
we went without them, but I can live with them if you strongly
think they're better than the alternative. If you keep them,
please convert the BUG_ON() to ASSERT() though, to be in
line with the #ifdef side.
Jan
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