Re: [Xen-devel] [PATCH 2/5] xen/alternatives: Plumb a 'live' parameter through apply_alternatives()

[Julien Grall <julien.grall@xxxxxxx>]

Hi Andrew,

On 29/01/18 15:38, Andrew Cooper wrote:
> On x86, we would like to alter how we patch based on whether there is any
> chance of the code being patched being concurrently executed.
>
> prepare_payload() passes false (as the livepatch definitely isn't live at this
> point), whereas the boot-time alternatives application passes true.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Julien Grall <julien.grall@xxxxxxx>
> CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> CC: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> ---
>   xen/arch/arm/alternative.c        | 10 ++++++----
>   xen/arch/x86/alternative.c        |  5 +++--
>   xen/common/livepatch.c            |  2 +-
>   xen/include/asm-arm/alternative.h |  6 ++++--
>   xen/include/asm-x86/alternative.h |  3 ++-
>   5 files changed, 16 insertions(+), 10 deletions(-)
>
> diff --git a/xen/arch/arm/alternative.c b/xen/arch/arm/alternative.c
> index 99112e1..078b259 100644
> --- a/xen/arch/arm/alternative.c
> +++ b/xen/arch/arm/alternative.c
> @@ -98,7 +98,8 @@ static u32 get_alt_insn(const struct alt_instr *alt,
>    * The region patched should be read-write to allow __apply_alternatives
>    * to replacing the instructions when necessary.
>    */
> -static void __apply_alternatives(const struct alt_region *region)
> +static void __apply_alternatives(const struct alt_region *region,
> +                                 bool live)
>   {
>       const struct alt_instr *alt;
>       const u32 *replptr;
> @@ -193,7 +194,7 @@ static int __init __apply_alternatives_multi_stop(void 
> *unused)
>           region.begin = (void *)__alt_instructions - (void *)_start + xenmap;
>           region.end = (void *)__alt_instructions_end - (void *)_start + xenmap;
>   
> -        __apply_alternatives(&region);
> +        __apply_alternatives(&region, true);
>   
>           unregister_virtual_region(&patch_region);
>   
> @@ -224,14 +225,15 @@ void __init apply_alternatives_all(void)
>   }
>   
>   void apply_alternatives(const struct alt_instr *start,
> -                        const struct alt_instr *end)
> +                        const struct alt_instr *end,
> +                        bool live)
This function is not able to deal with "live" code, so I think at least 
need an ASSERT(!live) to prevent mis-usage of the code.
With that:

Reviewed-by: Julien Grall <julien.grall@xxxxxxx>

Cheers,

--
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel