[PATCH v2 0/2] KVM: arm64: Expose CSV3 to guests on running on Meltdown-safe HW

[Will Deacon]

On Fri, Dec 04, 2020 at 06:37:07PM +0000, Marc Zyngier wrote:
> Will recently pointed out that when running on big-little systems that
> are known not to be vulnerable to Metldown, guests are not presented
> with the CSV3 property if the physical HW include a core that doesn't
> have CSV3, despite being known to be safe (it is on the kpti_safe_list).
> 
> Since this is valuable information that can be cheaply given to the
> guest, let's just do that. The scheme is the same as what we do for
> CSV2, allowing userspace to change the default setting if this doesn't
> advertise a safer setting than what the kernel thinks it is.
> 
> * From v1:
>   - Fix the clearing of ID_AA64PFR0_EL1.CSV3 on update from userspace
>   - Actually store the userspace value
> 
> Marc Zyngier (2):
>   arm64: Make the Meltdown mitigation state available
>   KVM: arm64: Advertise ID_AA64PFR0_EL1.CSV3=1 if the CPUs are
>     Meltdown-safe

Acked-by: Will Deacon <will at kernel.org>

Will