Re: [Xen-devel] [PATCH v3 04/10] Make MEM_ACCESS configurable

[Tamas K Lengyel <tamas.k.lengyel@xxxxxxxxx>]

On Wed, May 30, 2018 at 2:24 PM, Stefano Stabellini
<sstabellini@xxxxxxxxxx> wrote:
> On Tue, 29 May 2018, Jan Beulich wrote:
>> >>> On 23.05.18 at 02:25, <sstabellini@xxxxxxxxxx> wrote:
>> > --- a/xen/arch/arm/Kconfig
>> > +++ b/xen/arch/arm/Kconfig
>> > @@ -26,6 +26,9 @@ config ARCH_DEFCONFIG
>> >     default "arch/arm/configs/arm32_defconfig" if ARM_32
>> >     default "arch/arm/configs/arm64_defconfig" if ARM_64
>> >
>> > +config HAS_MEM_ACCESS
>> > +   def_bool y
>>
>> The more that you're not deleting the respective select-s, please
>> don't introduce such per-arch. Keep the arch-neutral one, ...
>
> OK
>
>
>> > @@ -30,6 +31,12 @@ config ARCH_DEFCONFIG
>> >     string
>> >     default "arch/x86/configs/x86_64_defconfig"
>> >
>> > +config HAS_MEM_ACCESS
>> > +   def_bool y
>> > +
>> > +config MEM_ACCESS_ALWAYS_ON
>> > +   def_bool y
>>
>> ... make this one similarly an arch-neutral one (select-ed further up
>> in this file).
>
> OK
>
>
>> > --- a/xen/common/Kconfig
>> > +++ b/xen/common/Kconfig
>> > @@ -20,8 +20,15 @@ config HAS_DEVICE_TREE
>> >  config HAS_EX_TABLE
>> >     bool
>> >
>> > -config HAS_MEM_ACCESS
>> > +config MEM_ACCESS
>> >     bool
>> > +   prompt "Memory Access and VM events" if !MEM_ACCESS_ALWAYS_ON
>> > +   default y
>>
>> Please combine bool and default to def_bool.
>
> OK
>
>
>> Also - do we perhaps want the
>> prompt to additionally have an EXPERT dependency? Without you saying why
>> you want this configurable I can't tell whether this would make sense.
>
> I am doing this mostly to reduce the code size. I think we should
> security support configurations without MEM_ACCESS. I also don't think
> it should take an "expert" to disable MEM_ACCESS in Xen. Thus, my
> preference is to avoid adding the EXPERT dependency.

IMHO for ARM mem_access can be off by default. It is still experimental.

Tamas

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