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From:   Fabiano Rosas <farosas@linux.ibm.com>
To:     Ravi Bangoria <ravi.bangoria@linux.ibm.com>, mpe@ellerman.id.au,
        paulus@samba.org
Cc:     ravi.bangoria@linux.ibm.com, mikey@neuling.org, npiggin@gmail.com,
        leobras.c@gmail.com, pbonzini@redhat.com, christophe.leroy@c-s.fr,
        jniethe5@gmail.com, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v2 1/4] KVM: PPC: Allow nested guest creation when L0 hv_guest_state > L1
In-Reply-To: <20201124105953.39325-2-ravi.bangoria@linux.ibm.com>
References: <20201124105953.39325-1-ravi.bangoria@linux.ibm.com> <20201124105953.39325-2-ravi.bangoria@linux.ibm.com>
Date:   Wed, 09 Dec 2020 11:25:24 -0300
Message-ID: <87r1nzgip7.fsf@linux.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Ravi Bangoria <ravi.bangoria@linux.ibm.com> writes:

> On powerpc, L1 hypervisor takes help of L0 using H_ENTER_NESTED
> hcall to load L2 guest state in cpu. L1 hypervisor prepares the
> L2 state in struct hv_guest_state and passes a pointer to it via
> hcall. Using that pointer, L0 reads/writes that state directly
> from/to L1 memory. Thus L0 must be aware of hv_guest_state layout
> of L1. Currently it uses version field to achieve this. i.e. If
> L0 hv_guest_state.version != L1 hv_guest_state.version, L0 won't
> allow nested kvm guest.
>
> This restriction can be loosen up a bit. L0 can be taught to
> understand older layout of hv_guest_state, if we restrict the
> new member to be added only at the end. i.e. we can allow
> nested guest even when L0 hv_guest_state.version > L1
> hv_guest_state.version. Though, the other way around is not
> possible.
>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>

Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>

> ---
>  arch/powerpc/include/asm/hvcall.h   | 17 +++++++--
>  arch/powerpc/kvm/book3s_hv_nested.c | 53 ++++++++++++++++++++++++-----
>  2 files changed, 59 insertions(+), 11 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/hvcall.h b/arch/powerpc/include/asm/hvcall.h
> index fbb377055471..a7073fddb657 100644
> --- a/arch/powerpc/include/asm/hvcall.h
> +++ b/arch/powerpc/include/asm/hvcall.h
> @@ -524,9 +524,12 @@ struct h_cpu_char_result {
>  	u64 behaviour;
>  };
>
> -/* Register state for entering a nested guest with H_ENTER_NESTED */
> +/*
> + * Register state for entering a nested guest with H_ENTER_NESTED.
> + * New member must be added at the end.
> + */
>  struct hv_guest_state {
> -	u64 version;		/* version of this structure layout */
> +	u64 version;		/* version of this structure layout, must be first */
>  	u32 lpid;
>  	u32 vcpu_token;
>  	/* These registers are hypervisor privileged (at least for writing) */
> @@ -560,6 +563,16 @@ struct hv_guest_state {
>  /* Latest version of hv_guest_state structure */
>  #define HV_GUEST_STATE_VERSION	1
>
> +static inline int hv_guest_state_size(unsigned int version)
> +{
> +	switch (version) {
> +	case 1:
> +		return offsetofend(struct hv_guest_state, ppr);
> +	default:
> +		return -1;
> +	}
> +}
> +
>  #endif /* __ASSEMBLY__ */
>  #endif /* __KERNEL__ */
>  #endif /* _ASM_POWERPC_HVCALL_H */
> diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c
> index 33b58549a9aa..2b433c3bacea 100644
> --- a/arch/powerpc/kvm/book3s_hv_nested.c
> +++ b/arch/powerpc/kvm/book3s_hv_nested.c
> @@ -215,6 +215,45 @@ static void kvmhv_nested_mmio_needed(struct kvm_vcpu *vcpu, u64 regs_ptr)
>  	}
>  }
>
> +static int kvmhv_read_guest_state_and_regs(struct kvm_vcpu *vcpu,
> +					   struct hv_guest_state *l2_hv,
> +					   struct pt_regs *l2_regs,
> +					   u64 hv_ptr, u64 regs_ptr)
> +{
> +	int size;
> +
> +	if (kvm_vcpu_read_guest(vcpu, hv_ptr, &(l2_hv->version),
> +				sizeof(l2_hv->version)))
> +		return -1;
> +
> +	if (kvmppc_need_byteswap(vcpu))
> +		l2_hv->version = swab64(l2_hv->version);
> +
> +	size = hv_guest_state_size(l2_hv->version);
> +	if (size < 0)
> +		return -1;
> +
> +	return kvm_vcpu_read_guest(vcpu, hv_ptr, l2_hv, size) ||
> +		kvm_vcpu_read_guest(vcpu, regs_ptr, l2_regs,
> +				    sizeof(struct pt_regs));
> +}
> +
> +static int kvmhv_write_guest_state_and_regs(struct kvm_vcpu *vcpu,
> +					    struct hv_guest_state *l2_hv,
> +					    struct pt_regs *l2_regs,
> +					    u64 hv_ptr, u64 regs_ptr)
> +{
> +	int size;
> +
> +	size = hv_guest_state_size(l2_hv->version);
> +	if (size < 0)
> +		return -1;
> +
> +	return kvm_vcpu_write_guest(vcpu, hv_ptr, l2_hv, size) ||
> +		kvm_vcpu_write_guest(vcpu, regs_ptr, l2_regs,
> +				     sizeof(struct pt_regs));
> +}
> +
>  long kvmhv_enter_nested_guest(struct kvm_vcpu *vcpu)
>  {
>  	long int err, r;
> @@ -235,17 +274,15 @@ long kvmhv_enter_nested_guest(struct kvm_vcpu *vcpu)
>  	hv_ptr = kvmppc_get_gpr(vcpu, 4);
>  	regs_ptr = kvmppc_get_gpr(vcpu, 5);
>  	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
> -	err = kvm_vcpu_read_guest(vcpu, hv_ptr, &l2_hv,
> -				  sizeof(struct hv_guest_state)) ||
> -		kvm_vcpu_read_guest(vcpu, regs_ptr, &l2_regs,
> -				    sizeof(struct pt_regs));
> +	err = kvmhv_read_guest_state_and_regs(vcpu, &l2_hv, &l2_regs,
> +					      hv_ptr, regs_ptr);
>  	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
>  	if (err)
>  		return H_PARAMETER;
>
>  	if (kvmppc_need_byteswap(vcpu))
>  		byteswap_hv_regs(&l2_hv);
> -	if (l2_hv.version != HV_GUEST_STATE_VERSION)
> +	if (l2_hv.version > HV_GUEST_STATE_VERSION)
>  		return H_P2;
>
>  	if (kvmppc_need_byteswap(vcpu))
> @@ -325,10 +362,8 @@ long kvmhv_enter_nested_guest(struct kvm_vcpu *vcpu)
>  		byteswap_pt_regs(&l2_regs);
>  	}
>  	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
> -	err = kvm_vcpu_write_guest(vcpu, hv_ptr, &l2_hv,
> -				   sizeof(struct hv_guest_state)) ||
> -		kvm_vcpu_write_guest(vcpu, regs_ptr, &l2_regs,
> -				   sizeof(struct pt_regs));
> +	err = kvmhv_write_guest_state_and_regs(vcpu, &l2_hv, &l2_regs,
> +					       hv_ptr, regs_ptr);
>  	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
>  	if (err)
>  		return H_AUTHORITY;