Re: [PATCH v5 2/2] KVM: PPC: Book3S HV: Stop forwarding all HFUs to L1

[Nicholas Piggin <npiggin@gmail.com>]

Excerpts from Fabiano Rosas's message of July 27, 2021 6:17 am:
> If the nested hypervisor has no access to a facility because it has
> been disabled by the host, it should also not be able to see the
> Hypervisor Facility Unavailable that arises from one of its guests
> trying to access the facility.
> 
> This patch turns a HFU that happened in L2 into a Hypervisor Emulation
> Assistance interrupt and forwards it to L1 for handling. The ones that
> happened because L1 explicitly disabled the facility for L2 are still
> let through, along with the corresponding Cause bits in the HFSCR.
> 
> Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
> Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>  arch/powerpc/kvm/book3s_hv_nested.c | 32 +++++++++++++++++++++++------
>  1 file changed, 26 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c
> index 8215dbd4be9a..d544b092b49a 100644
> --- a/arch/powerpc/kvm/book3s_hv_nested.c
> +++ b/arch/powerpc/kvm/book3s_hv_nested.c
> @@ -99,7 +99,7 @@ static void byteswap_hv_regs(struct hv_guest_state *hr)
>  	hr->dawrx1 = swab64(hr->dawrx1);
>  }
>  
> -static void save_hv_return_state(struct kvm_vcpu *vcpu, int trap,
> +static void save_hv_return_state(struct kvm_vcpu *vcpu,
>  				 struct hv_guest_state *hr)
>  {
>  	struct kvmppc_vcore *vc = vcpu->arch.vcore;
> @@ -118,7 +118,7 @@ static void save_hv_return_state(struct kvm_vcpu *vcpu, int trap,
>  	hr->pidr = vcpu->arch.pid;
>  	hr->cfar = vcpu->arch.cfar;
>  	hr->ppr = vcpu->arch.ppr;
> -	switch (trap) {
> +	switch (vcpu->arch.trap) {
>  	case BOOK3S_INTERRUPT_H_DATA_STORAGE:
>  		hr->hdar = vcpu->arch.fault_dar;
>  		hr->hdsisr = vcpu->arch.fault_dsisr;
> @@ -128,9 +128,29 @@ static void save_hv_return_state(struct kvm_vcpu *vcpu, int trap,
>  		hr->asdr = vcpu->arch.fault_gpa;
>  		break;
>  	case BOOK3S_INTERRUPT_H_FAC_UNAVAIL:
> -		hr->hfscr = ((~HFSCR_INTR_CAUSE & hr->hfscr) |
> -			     (HFSCR_INTR_CAUSE & vcpu->arch.hfscr));
> -		break;
> +	{
> +		u8 cause = vcpu->arch.hfscr >> 56;

Can this be u64 just to help gcc?

> +
> +		WARN_ON_ONCE(cause >= BITS_PER_LONG);
> +
> +		if (!(hr->hfscr & (1UL << cause))) {
> +			hr->hfscr = ((~HFSCR_INTR_CAUSE & hr->hfscr) |
> +				     (HFSCR_INTR_CAUSE & vcpu->arch.hfscr));
> +			break;
> +		}
> +
> +		/*
> +		 * We have disabled this facility, so it does not
> +		 * exist from L1's perspective. Turn it into a HEAI.
> +		 */
> +		vcpu->arch.trap = BOOK3S_INTERRUPT_H_EMUL_ASSIST;
> +		kvmppc_load_last_inst(vcpu, INST_GENERIC, &vcpu->arch.emul_inst);

Hmm, this doesn't handle kvmpc_load_last_inst failure. Other code tends 
to just resume guest and retry in this case. Can we do that here?

> +
> +		/* Don't leak the cause field */
> +		hr->hfscr &= ~HFSCR_INTR_CAUSE;

This hunk also remains -- shouldn't change HFSCR for HEA, only HFAC.

Thanks,
Nick