Re: [Xen-devel] [PATCH 3 of 7] Use a reserved pfn in the guest address space to store mem event rings

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-02-23 at 06:05 +0000, Andres Lagar-Cavilla wrote:

Doers this mean that a guest can now potentially observe, or even modify
it's own mem event ring? Are we sure there's no potential for havoc
here?

Is there no scope for making these pages owned by the domain but not
actually part of the P2M? We can cope with that for other types of magic
page, can't we?

I didn't atually dig into the implementation other than to see if it
answered  my questions, although I did notice:

> diff -r 99e6c9b9e971 -r 0e79f8005b6b tools/libxc/xc_hvm_build.c
> --- a/tools/libxc/xc_hvm_build.c
> +++ b/tools/libxc/xc_hvm_build.c
> @@ -38,12 +38,15 @@
>  #define SUPERPAGE_1GB_SHIFT   18
>  #define SUPERPAGE_1GB_NR_PFNS (1UL << SUPERPAGE_1GB_SHIFT)
> 
> -#define SPECIALPAGE_BUFIOREQ 0
> -#define SPECIALPAGE_XENSTORE 1
> -#define SPECIALPAGE_IOREQ    2
> -#define SPECIALPAGE_IDENT_PT 3
> -#define SPECIALPAGE_CONSOLE  4
> -#define NR_SPECIAL_PAGES     5
> +#define SPECIALPAGE_PAGING   0
> +#define SPECIALPAGE_ACCESS   1
> +#define SPECIALPAGE_SHARING  2
> +#define SPECIALPAGE_BUFIOREQ 3
> +#define SPECIALPAGE_XENSTORE 4
> +#define SPECIALPAGE_IOREQ    5
> +#define SPECIALPAGE_IDENT_PT 6
> +#define SPECIALPAGE_CONSOLE  7
> +#define NR_SPECIAL_PAGES     8

Any reason to not simply append them?

Ian.


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