[PATCH 3/4] KVM: arm64: nv: Don't mask VTCR_EL2.HA if FEAT_HAFDBS is present

[Marc Zyngier]

On Fri, 28 Nov 2025 18:48:10 +0000,
Oliver Upton <oupton at kernel.org> wrote:
> 
> On Fri, Nov 28, 2025 at 03:46:44PM +0000, Marc Zyngier wrote:
> > On Fri, 28 Nov 2025 10:09:45 +0000,
> > Alexandru Elisei <alexandru.elisei at arm.com> wrote:
> > > 
> > > Commit 39db933ba67f ("KVM: arm64: nv: Implement HW access flag management
> > > in stage-2 SW PTW") added support for hardware updates to the access flag
> > > to stage 2 if the feature is available to the virtual machine, but forgot
> > > to remove the VTCR_EL2.HA bit from the res0 mask for the register. Remove
> > > it from the mask to allow the VM to use the feature.
> > > 
> > > Fixes: 39db933ba67f ("KVM: arm64: nv: Implement HW access flag management in stage-2 SW PTW")
> > > Signed-off-by: Alexandru Elisei <alexandru.elisei at arm.com>
> > > ---
> > >  arch/arm64/kvm/nested.c | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
> > > index 911fc99ed99d..7a34163f6c68 100644
> > > --- a/arch/arm64/kvm/nested.c
> > > +++ b/arch/arm64/kvm/nested.c
> > > @@ -1719,7 +1719,9 @@ int kvm_init_nv_sysregs(struct kvm_vcpu *vcpu)
> > >  	set_sysreg_masks(kvm, VTTBR_EL2, res0, res1);
> > >  
> > >  	/* VTCR_EL2 */
> > > -	res0 = GENMASK(63, 32) | GENMASK(30, 20);
> > > +	res0 = GENMASK(63, 32) | GENMASK(30, 22) | BIT(20);
> > > +	if (!kvm_has_feat(kvm, ID_AA64MMFR1_EL1, HAFDBS, AF))
> > > +		res0 |= VTCR_EL2_HA;
> > >  	res1 = BIT(31);
> > >  	set_sysreg_masks(kvm, VTCR_EL2, res0, res1);
> > >  
> > 
> > The fix is correct, but I really do not want to add more of these
> > tedious checks, one after the other. We should fix this once and for
> > all by converting VTCR_EL2 to the feature dependency infrastructure
> > and be done with it.
> > 
> > I've pushed a small series at [1] that does that (very lightly
> > tested).
> 
> This looks alright to me, do you want to post it?

Still fixing some of the fallout from the sysreg conversion -- a bunch
of things that were shifted constants are now unshifted, and need to
be FIELD_PREP()'d.

I *think* I got them all now, but this is all a bit fiddly. Should the
last tests run smoothly,

Note that the TCR conversion will be even more invasive, and probably
not merge window material, so you may want to pick Alexandru's 4th
patch as well.

Thanks,

	M.

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