[PATCH 07/10] KVM: arm64: Save guest's ZCR_EL1 before saving the FPSIMD state

[Will Deacon]

On Wed, Mar 17, 2021 at 05:17:38PM +0000, Will Deacon wrote:
> On Tue, Mar 16, 2021 at 10:13:09AM +0000, Marc Zyngier wrote:
> > Make sure the guest's ZCR_EL1 is saved before we save/flush the
> > state. This will be useful in later patches.
> > 
> > Signed-off-by: Marc Zyngier <maz at kernel.org>
> > ---
> >  arch/arm64/kvm/fpsimd.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
> > index 84afca5ed6f2..b5f95abd23f5 100644
> > --- a/arch/arm64/kvm/fpsimd.c
> > +++ b/arch/arm64/kvm/fpsimd.c
> > @@ -121,10 +121,10 @@ void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu)
> >  	local_irq_save(flags);
> >  
> >  	if (vcpu->arch.flags & KVM_ARM64_FP_ENABLED) {
> > -		fpsimd_save_and_flush_cpu_state();
> > -
> >  		if (guest_has_sve)
> >  			__vcpu_sys_reg(vcpu, ZCR_EL1) = read_sysreg_el1(SYS_ZCR);
> > +
> > +		fpsimd_save_and_flush_cpu_state();
> 
> I _think_ fpsimd_save_and_flush_cpu_state() contains a RDVL instruction
> to get at the vector length for sve_get_vl(), and this ends up reading from
> ZCR_EL1. So I'm not sure it's save to move it like this.

Duh, we're not changing the register here, but just saving it off. So it's
fine:

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

Will