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Date:   Fri, 5 Feb 2021 15:05:08 +0100
From:   Claudio Imbrenda <imbrenda@linux.ibm.com>
To:     Janosch Frank <frankja@linux.ibm.com>
Cc:     linux-kernel@vger.kernel.org, borntraeger@de.ibm.com,
        david@redhat.com, kvm@vger.kernel.org, linux-s390@vger.kernel.org,
        stable@vger.kernel.org
Subject: Re: [PATCH v2 1/2] s390/kvm: extend kvm_s390_shadow_fault to return
 entry pointer
Message-ID: <20210205150508.75789dd0@ibm-vm>
In-Reply-To: <9eb63005-a11f-a56a-d7e1-c65dd9e8d9a2@linux.ibm.com>
References: <20210202180028.876888-1-imbrenda@linux.ibm.com>
 <20210202180028.876888-2-imbrenda@linux.ibm.com>
 <16522b25-a590-fbc4-0eb6-3537d8032577@linux.ibm.com>
 <20210205131555.0b4f32d1@ibm-vm>
 <9eb63005-a11f-a56a-d7e1-c65dd9e8d9a2@linux.ibm.com>
Organization: IBM
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On Fri, 5 Feb 2021 13:56:53 +0100
Janosch Frank <frankja@linux.ibm.com> wrote:

> On 2/5/21 1:15 PM, Claudio Imbrenda wrote:
> > On Thu, 4 Feb 2021 17:34:00 +0100
> > Janosch Frank <frankja@linux.ibm.com> wrote:
> >   
> >> On 2/2/21 7:00 PM, Claudio Imbrenda wrote:  
> >>> Extend kvm_s390_shadow_fault to return the pointer to the valid
> >>> leaf DAT table entry, or to the invalid entry.
> >>>
> >>> Also return some flags in the lower bits of the address:
> >>> DAT_PROT: indicates that DAT protection applies because of the
> >>>           protection bit in the segment (or, if EDAT, region)
> >>> tables NOT_PTE: indicates that the address of the DAT table entry
> >>> returned does not refer to a PTE, but to a segment or region
> >>> table.
> >>>
> >>> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> >>> Cc: stable@vger.kernel.org
> >>> ---
> >>>  arch/s390/kvm/gaccess.c | 26 ++++++++++++++++++++++----
> >>>  arch/s390/kvm/gaccess.h |  5 ++++-
> >>>  arch/s390/kvm/vsie.c    |  8 ++++----
> >>>  3 files changed, 30 insertions(+), 9 deletions(-)
> >>>
> >>> diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
> >>> index 6d6b57059493..2d7bcbfb185e 100644
> >>> --- a/arch/s390/kvm/gaccess.c
> >>> +++ b/arch/s390/kvm/gaccess.c
> >>> @@ -1034,6 +1034,7 @@ static int kvm_s390_shadow_tables(struct
> >>> gmap *sg, unsigned long saddr, rfte.val = ptr;
> >>>  			goto shadow_r2t;
> >>>  		}
> >>> +		*pgt = ptr + vaddr.rfx * 8;    
> >>
> >> So pgt either is a table entry if rc > 0 or a pointer to the first
> >> pte on rc == 0 after this change?  
> > 
> > yes
> >   
> >> Hrm, if it is really based on RCs than I might be able to come to
> >> terms with having two things in a ptr with the name pgt. But it
> >> needs a comment change.  
> > 
> > will do.
> >   
> >>>  		rc = gmap_read_table(parent, ptr + vaddr.rfx * 8,
> >>> &rfte.val); if (rc)
> >>>  			return rc;
> >>> @@ -1060,6 +1061,7 @@ static int kvm_s390_shadow_tables(struct
> >>> gmap *sg, unsigned long saddr, rste.val = ptr;
> >>>  			goto shadow_r3t;
> >>>  		}
> >>> +		*pgt = ptr + vaddr.rsx * 8;
> >>>  		rc = gmap_read_table(parent, ptr + vaddr.rsx * 8,
> >>> &rste.val); if (rc)
> >>>  			return rc;
> >>> @@ -1087,6 +1089,7 @@ static int kvm_s390_shadow_tables(struct
> >>> gmap *sg, unsigned long saddr, rtte.val = ptr;
> >>>  			goto shadow_sgt;
> >>>  		}
> >>> +		*pgt = ptr + vaddr.rtx * 8;
> >>>  		rc = gmap_read_table(parent, ptr + vaddr.rtx * 8,
> >>> &rtte.val); if (rc)
> >>>  			return rc;
> >>> @@ -1123,6 +1126,7 @@ static int kvm_s390_shadow_tables(struct
> >>> gmap *sg, unsigned long saddr, ste.val = ptr;
> >>>  			goto shadow_pgt;
> >>>  		}
> >>> +		*pgt = ptr + vaddr.sx * 8;
> >>>  		rc = gmap_read_table(parent, ptr + vaddr.sx * 8,
> >>> &ste.val); if (rc)
> >>>  			return rc;
> >>> @@ -1157,6 +1161,8 @@ static int kvm_s390_shadow_tables(struct
> >>> gmap *sg, unsigned long saddr,
> >>>   * @vcpu: virtual cpu
> >>>   * @sg: pointer to the shadow guest address space structure
> >>>   * @saddr: faulting address in the shadow gmap
> >>> + * @pteptr: will contain the address of the faulting DAT table
> >>> entry, or of
> >>> + *          the valid leaf, plus some flags    
> >>
> >> pteptr is not the right name if it can be two things  
> > 
> > it cannot be two things there, kvm_s390_shadow_fault always returns
> > a DAT _entry_ (pte, segment, region).  
> 
> And that's exactly what I meant, it's not a pteptr i.e. not a (pte_t
> *) as the name would suggest.

fair enough, I'll rename it to something like entryptr or so

> 
> >   
> >>>   *
> >>>   * Returns: - 0 if the shadow fault was successfully resolved
> >>>   *	    - > 0 (pgm exception code) on exceptions while
> >>> faulting @@ -1165,11 +1171,11 @@ static int
> >>> kvm_s390_shadow_tables(struct gmap *sg, unsigned long saddr,
> >>>   *	    - -ENOMEM if out of memory
> >>>   */
> >>>  int kvm_s390_shadow_fault(struct kvm_vcpu *vcpu, struct gmap *sg,
> >>> -			  unsigned long saddr)
> >>> +			  unsigned long saddr, unsigned long
> >>> *pteptr) {
> >>>  	union vaddress vaddr;
> >>>  	union page_table_entry pte;
> >>> -	unsigned long pgt;
> >>> +	unsigned long pgt = 0;
> >>>  	int dat_protection, fake;
> >>>  	int rc;
> >>>  
> >>> @@ -1191,8 +1197,20 @@ int kvm_s390_shadow_fault(struct kvm_vcpu
> >>> *vcpu, struct gmap *sg, pte.val = pgt + vaddr.px * PAGE_SIZE;
> >>>  		goto shadow_page;
> >>>  	}
> >>> -	if (!rc)
> >>> -		rc = gmap_read_table(sg->parent, pgt + vaddr.px *
> >>> 8, &pte.val); +
> >>> +	switch (rc) {
> >>> +	case PGM_SEGMENT_TRANSLATION:
> >>> +	case PGM_REGION_THIRD_TRANS:
> >>> +	case PGM_REGION_SECOND_TRANS:
> >>> +	case PGM_REGION_FIRST_TRANS:
> >>> +		pgt |= NOT_PTE;    
> >>
> >> GACC_TRANSL_ENTRY_INV ?  
> > 
> > no, this is only for non-pte entries
> >   
> >>> +		break;
> >>> +	case 0:
> >>> +		pgt += vaddr.px * 8;
> >>> +		rc = gmap_read_table(sg->parent, pgt, &pte.val);
> >>> +	}
> >>> +	if (*pteptr)
> >>> +		*pteptr = pgt | dat_protection * DAT_PROT;
> >>>  	if (!rc && pte.i)
> >>>  		rc = PGM_PAGE_TRANSLATION;
> >>>  	if (!rc && pte.z)
> >>> diff --git a/arch/s390/kvm/gaccess.h b/arch/s390/kvm/gaccess.h
> >>> index f4c51756c462..66a6e2cec97a 100644
> >>> --- a/arch/s390/kvm/gaccess.h
> >>> +++ b/arch/s390/kvm/gaccess.h
> >>> @@ -359,7 +359,10 @@ void ipte_unlock(struct kvm_vcpu *vcpu);
> >>>  int ipte_lock_held(struct kvm_vcpu *vcpu);
> >>>  int kvm_s390_check_low_addr_prot_real(struct kvm_vcpu *vcpu,
> >>> unsigned long gra); 
> >>> +#define DAT_PROT 2    
> >>
> >> GACC_TRANSL_ENTRY_PROT  
> > 
> > this is also only for non-pte entries
> >   
> >>> +#define NOT_PTE 4
> >>> +
> >>>  int kvm_s390_shadow_fault(struct kvm_vcpu *vcpu, struct gmap
> >>> *shadow,
> >>> -			  unsigned long saddr);
> >>> +			  unsigned long saddr, unsigned long
> >>> *pteptr); 
> >>>  #endif /* __KVM_S390_GACCESS_H */
> >>> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> >>> index c5d0a58b2c29..7db022141db3 100644
> >>> --- a/arch/s390/kvm/vsie.c
> >>> +++ b/arch/s390/kvm/vsie.c
> >>> @@ -619,10 +619,10 @@ static int map_prefix(struct kvm_vcpu *vcpu,
> >>> struct vsie_page *vsie_page) /* with mso/msl, the prefix lies at
> >>> offset *mso* */ prefix += scb_s->mso;
> >>>  
> >>> -	rc = kvm_s390_shadow_fault(vcpu, vsie_page->gmap,
> >>> prefix);
> >>> +	rc = kvm_s390_shadow_fault(vcpu, vsie_page->gmap, prefix,
> >>> NULL); if (!rc && (scb_s->ecb & ECB_TE))
> >>>  		rc = kvm_s390_shadow_fault(vcpu, vsie_page->gmap,
> >>> -					   prefix + PAGE_SIZE);
> >>> +					   prefix + PAGE_SIZE,
> >>> NULL); /*
> >>>  	 * We don't have to mprotect, we will be called for all
> >>> unshadows.
> >>>  	 * SIE will detect if protection applies and trigger a
> >>> validity. @@ -913,7 +913,7 @@ static int handle_fault(struct
> >>> kvm_vcpu *vcpu, struct vsie_page *vsie_page)
> >>> current->thread.gmap_addr, 1); 
> >>>  	rc = kvm_s390_shadow_fault(vcpu, vsie_page->gmap,
> >>> -				   current->thread.gmap_addr);
> >>> +				   current->thread.gmap_addr,
> >>> NULL); if (rc > 0) {
> >>>  		rc = inject_fault(vcpu, rc,
> >>>  				  current->thread.gmap_addr,
> >>> @@ -935,7 +935,7 @@ static void handle_last_fault(struct kvm_vcpu
> >>> *vcpu, {
> >>>  	if (vsie_page->fault_addr)
> >>>  		kvm_s390_shadow_fault(vcpu, vsie_page->gmap,
> >>> -				      vsie_page->fault_addr);
> >>> +				      vsie_page->fault_addr,
> >>> NULL);    
> >>
> >> Ok
> >>  
> >>>  	vsie_page->fault_addr = 0;
> >>>  }
> >>>  
> >>>     
> >>  
> >   
>