Re: [PATCH 0/7] KVM: arm64: Hypervisor stack enhancements

[Kalesh Singh]

On Mon, Feb 14, 2022 at 3:41 AM Marc Zyngier <maz@xxxxxxxxxx> wrote:
>
> On Thu, 10 Feb 2022 22:41:41 +0000,
> Kalesh Singh <kaleshsingh@xxxxxxxxxx> wrote:
> >
> > This series is based on v5.17-rc3 and adds the following stack features to
> > the KVM nVHE hypervisor:
> >
> > == Hyp Stack Guard Pages ==
> >
> > Based on the technique used by arm64 VMAP_STACK to detect overflow.
> > i.e. the stack is aligned to twice its size which ensure that the
> > 'stack shift' bit of any valid SP is 0. The 'stack shift' bit can be
> > tested in the exception entry to detect overflow without corrupting GPRs.
>
> Having quickly parsed the code, this seems to only be effective for
> pKVM and the EL2-allocated stack. Is there any technical reason not to
> implement this for the much more common case of 'classic' KVM in nVHE
> mode?

Hi Marc,

No technical reason. We hadn't thought of it from that perspective.
It's a good idea, I'll look into this and repost  a new version.

Thanks,
Kalesh

>
> Thanks,
>
>         M.
>
> --
> Without deviation from the norm, progress is not possible.