linux-kernel - Re: [PATCH 1/6] KVM: s390/vfio-ap: Use kvm_is_gpa_in_memslot() instead of open coded equivalent

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Message-ID: <459f6b6f-4c51-492f-a137-637bb61d17bd@linux.ibm.com>
Date: Tue, 12 Aug 2025 15:40:46 -0400
From: Anthony Krowiak <akrowiak@...ux.ibm.com>
To: Sean Christopherson <seanjc@...gle.com>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Andy Lutomirski
 <luto@...nel.org>, Xin Li <xin@...or.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Kirill A. Shutemov" <kas@...nel.org>,
        Halil Pasic <pasic@...ux.ibm.com>, Jason Herne <jjherne@...ux.ibm.com>,
        Harald Freudenberger <freude@...ux.ibm.com>,
        Holger Dengler <dengler@...ux.ibm.com>
Cc: linuxppc-dev@...ts.ozlabs.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        linux-sgx@...r.kernel.org, x86@...nel.org, linux-coco@...ts.linux.dev,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH 1/6] KVM: s390/vfio-ap: Use kvm_is_gpa_in_memslot()
 instead of open coded equivalent



On 7/29/25 1:42 PM, Sean Christopherson wrote:
> Use kvm_is_gpa_in_memslot() to check the validity of the notification
> indicator byte address instead of open coding equivalent logic in the VFIO
> AP driver.
>
> Opportunistically use a dedicated wrapper that exists and is exported
> expressly for the VFIO AP module.  kvm_is_gpa_in_memslot() is generally
> unsuitable for use outside of KVM; other drivers typically shouldn't rely
> on KVM's memslots, and using the API requires kvm->srcu (or slots_lock) to
> be held for the entire duration of the usage, e.g. to avoid TOCTOU bugs.
> handle_pqap() is a bit of a special case, as it's explicitly invoked from
> KVM with kvm->srcu already held, and the VFIO AP driver is in many ways an
> extension of KVM that happens to live in a separate module.
>
> Providing a dedicated API for the VFIO AP driver will allow restricting
> the vast majority of generic KVM's exports to KVM submodules (e.g. to x86's
> kvm-{amd,intel}.ko vendor mdoules).
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Acked-by: Anthony Krowiak <akrowiak@...ux.ibm.com>

I only reviewed this patch in the series.

> ---
>   arch/s390/include/asm/kvm_host.h  | 2 ++
>   arch/s390/kvm/priv.c              | 8 ++++++++
>   drivers/s390/crypto/vfio_ap_ops.c | 2 +-
>   3 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index cb89e54ada25..449bc34e7cc3 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -719,6 +719,8 @@ bool kvm_s390_pv_cpu_is_protected(struct kvm_vcpu *vcpu);
>   extern int kvm_s390_gisc_register(struct kvm *kvm, u32 gisc);
>   extern int kvm_s390_gisc_unregister(struct kvm *kvm, u32 gisc);
>   
> +bool kvm_s390_is_gpa_in_memslot(struct kvm *kvm, gpa_t gpa);
> +
>   static inline void kvm_arch_free_memslot(struct kvm *kvm,
>   					 struct kvm_memory_slot *slot) {}
>   static inline void kvm_arch_memslots_updated(struct kvm *kvm, u64 gen) {}
> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
> index 9253c70897a8..7773e1e323bc 100644
> --- a/arch/s390/kvm/priv.c
> +++ b/arch/s390/kvm/priv.c
> @@ -605,6 +605,14 @@ static int handle_io_inst(struct kvm_vcpu *vcpu)
>   	}
>   }
>   
> +#if IS_ENABLED(CONFIG_VFIO_AP)
> +bool kvm_s390_is_gpa_in_memslot(struct kvm *kvm, gpa_t gpa)
> +{
> +	return kvm_is_gpa_in_memslot(kvm, gpa);
> +}
> +EXPORT_SYMBOL_GPL_FOR_MODULES(kvm_s390_is_gpa_in_memslot, "vfio_ap");
> +#endif
> +
>   /*
>    * handle_pqap: Handling pqap interception
>    * @vcpu: the vcpu having issue the pqap instruction
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> index 766557547f83..eb5ff49f6fe7 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -354,7 +354,7 @@ static int vfio_ap_validate_nib(struct kvm_vcpu *vcpu, dma_addr_t *nib)
>   
>   	if (!*nib)
>   		return -EINVAL;
> -	if (kvm_is_error_hva(gfn_to_hva(vcpu->kvm, *nib >> PAGE_SHIFT)))
> +	if (!kvm_s390_is_gpa_in_memslot(vcpu->kvm, *nib))
>   		return -EINVAL;
>   
>   	return 0;