linux-kernel - Re: [PATCH v3 1/3] s390: uv: UV feature check utility

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Date:   Tue, 15 Aug 2023 13:58:26 +0200
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     Steffen Eiden <seiden@...ux.ibm.com>, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, kvm@...r.kernel.org
Cc:     Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Michael Mueller <mimu@...ux.vnet.ibm.com>,
        Marc Hartmayer <mhartmay@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>
Subject: Re: [PATCH v3 1/3] s390: uv: UV feature check utility

On 8/10/23 13:32, Steffen Eiden wrote:
> Introduces a function to check the existence of an UV feature.
> Refactor feature bit checks to use the new function.
> 
> Reviewed-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> Signed-off-by: Steffen Eiden <seiden@...ux.ibm.com>

Please add a bounds check, then:
Reviewed-by: Janosch Frank <frankja@...ux.ibm.com>

> ---
>   arch/s390/include/asm/uv.h | 5 +++++
>   arch/s390/kernel/uv.c      | 2 +-
>   arch/s390/kvm/kvm-s390.c   | 2 +-
>   arch/s390/mm/fault.c       | 2 +-
>   4 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/s390/include/asm/uv.h b/arch/s390/include/asm/uv.h
> index d2cd42bb2c26..f76b2747b648 100644
> --- a/arch/s390/include/asm/uv.h
> +++ b/arch/s390/include/asm/uv.h
> @@ -397,6 +397,11 @@ struct uv_info {
>   
>   extern struct uv_info uv_info;
>   
> +static inline bool uv_has_feature(u8 feature_bit)
> +{

if (feature_bit >= sizeof(uv_info.uv_feature_indications) * 8)
	return false;

> +	return test_bit_inv(feature_bit, &uv_info.uv_feature_indications);
> +}
> +
>   #ifdef CONFIG_PROTECTED_VIRTUALIZATION_GUEST
>   extern int prot_virt_guest;
>   
> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
> index b771f1b4cdd1..fc07bc39e698 100644
> --- a/arch/s390/kernel/uv.c
> +++ b/arch/s390/kernel/uv.c
> @@ -258,7 +258,7 @@ static bool should_export_before_import(struct uv_cb_header *uvcb, struct mm_str
>   	 * shared page from a different protected VM will automatically also
>   	 * transfer its ownership.
>   	 */
> -	if (test_bit_inv(BIT_UV_FEAT_MISC, &uv_info.uv_feature_indications))
> +	if (uv_has_feature(BIT_UV_FEAT_MISC))
>   		return false;
>   	if (uvcb->cmd == UVC_CMD_UNPIN_PAGE_SHARED)
>   		return false;
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index e6511608280c..813cc3d59c90 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -2406,7 +2406,7 @@ static int kvm_s390_cpus_to_pv(struct kvm *kvm, u16 *rc, u16 *rrc)
>   	struct kvm_vcpu *vcpu;
>   
>   	/* Disable the GISA if the ultravisor does not support AIV. */
> -	if (!test_bit_inv(BIT_UV_FEAT_AIV, &uv_info.uv_feature_indications))
> +	if (!uv_has_feature(BIT_UV_FEAT_AIV))
>   		kvm_s390_gisa_disable(kvm);
>   
>   	kvm_for_each_vcpu(i, vcpu, kvm) {
> diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
> index b5e1bea9194c..8a86dd725870 100644
> --- a/arch/s390/mm/fault.c
> +++ b/arch/s390/mm/fault.c
> @@ -599,7 +599,7 @@ void do_secure_storage_access(struct pt_regs *regs)
>   	 * reliable without the misc UV feature so we need to check
>   	 * for that as well.
>   	 */
> -	if (test_bit_inv(BIT_UV_FEAT_MISC, &uv_info.uv_feature_indications) &&
> +	if (uv_has_feature(BIT_UV_FEAT_MISC) &&
>   	    !test_bit_inv(61, &regs->int_parm_long)) {
>   		/*
>   		 * When this happens, userspace did something that it