linux-kernel - Re: [PATCH v1 2/2] KVM: s390: Fix FOLL_*/FAULT_FLAG

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Message-ID: <5b0b8d5e-efab-4c5b-be1e-93d8a8f155b3@de.ibm.com>
Date: Tue, 5 Aug 2025 13:44:04 +0200
From: Christian Borntraeger <borntraeger@...ibm.com>
To: Claudio Imbrenda <imbrenda@...ux.ibm.com>, linux-kernel@...r.kernel.org
Cc: linux-s390@...r.kernel.org, kvm@...r.kernel.org, david@...hat.com,
        frankja@...ux.ibm.com, seiden@...ux.ibm.com, nsg@...ux.ibm.com,
        nrb@...ux.ibm.com, schlameuss@...ux.ibm.com, hca@...ux.ibm.com,
        mhartmay@...ux.ibm.com
Subject: Re: [PATCH v1 2/2] KVM: s390: Fix FOLL_*/FAULT_FLAG_* confusion

Am 05.08.25 um 13:14 schrieb Claudio Imbrenda:
> Pass the right type of flag to vcpu_dat_fault_handler(); it expects a
> FOLL_* flag (in particular FOLL_WRITE), but FAULT_FLAG_WRITE is passed
> instead.
> 
> This still works because they happen to have the same integer value,
> but it's a mistake, thus the fix.
> 
> Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> Fixes: 05066cafa925 ("s390/mm/fault: Handle guest-related program interrupts in KVM")

Acked-by: Christian Borntraeger <borntraeger@...ux.ibm.com>

Shouldnt we rename the parameter to __kvm_s390_handle_dat_fault and
vcpu_dat_fault_handler from flags to foll as well in their
implementation and prototypes to keep this consistent?

> ---
>   arch/s390/kvm/kvm-s390.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index d5ad10791c25..d41d77f2c7cd 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -4954,13 +4954,13 @@ static int vcpu_dat_fault_handler(struct kvm_vcpu *vcpu, unsigned long gaddr, un
>   
>   static int vcpu_post_run_handle_fault(struct kvm_vcpu *vcpu)
>   {
> -	unsigned int flags = 0;
> +	unsigned int foll = 0;
>   	unsigned long gaddr;
>   	int rc;
>   
>   	gaddr = current->thread.gmap_teid.addr * PAGE_SIZE;
>   	if (kvm_s390_cur_gmap_fault_is_write())
> -		flags = FAULT_FLAG_WRITE;
> +		foll = FOLL_WRITE;
>   
>   	switch (current->thread.gmap_int_code & PGM_INT_CODE_MASK) {
>   	case 0:
> @@ -5002,7 +5002,7 @@ static int vcpu_post_run_handle_fault(struct kvm_vcpu *vcpu)
>   			send_sig(SIGSEGV, current, 0);
>   		if (rc != -ENXIO)
>   			break;
> -		flags = FAULT_FLAG_WRITE;
> +		foll = FOLL_WRITE;
>   		fallthrough;
>   	case PGM_PROTECTION:
>   	case PGM_SEGMENT_TRANSLATION:
> @@ -5012,7 +5012,7 @@ static int vcpu_post_run_handle_fault(struct kvm_vcpu *vcpu)
>   	case PGM_REGION_SECOND_TRANS:
>   	case PGM_REGION_THIRD_TRANS:
>   		kvm_s390_assert_primary_as(vcpu);
> -		return vcpu_dat_fault_handler(vcpu, gaddr, flags);
> +		return vcpu_dat_fault_handler(vcpu, gaddr, foll);
>   	default:
>   		KVM_BUG(1, vcpu->kvm, "Unexpected program interrupt 0x%x, TEID 0x%016lx",
>   			current->thread.gmap_int_code, current->thread.gmap_teid.val);