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

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Message-ID: <20250805135931.0dbcf0f2@p-imbrenda>
Date: Tue, 5 Aug 2025 13:59:31 +0200
From: Claudio Imbrenda <imbrenda@...ux.ibm.com>
To: Christian Borntraeger <borntraeger@...ibm.com>
Cc: linux-kernel@...r.kernel.org, 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

On Tue, 5 Aug 2025 13:44:04 +0200
Christian Borntraeger <borntraeger@...ibm.com> wrote:

> 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?

that's a fair point

a patch in an upcoming series will do that, but I guess I can move that
change here instead.

I'll send a v2 later on today

> 
> > ---
> >   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);  
>