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From:   Janosch Frank <frankja@linux.ibm.com>
To:     Claudio Imbrenda <imbrenda@linux.ibm.com>,
        linux-kernel@vger.kernel.org
Cc:     borntraeger@de.ibm.com, david@redhat.com, kvm@vger.kernel.org,
        linux-s390@vger.kernel.org, stable@vger.kernel.org
References: <20210202180028.876888-1-imbrenda@linux.ibm.com>
 <20210202180028.876888-2-imbrenda@linux.ibm.com>
 <16522b25-a590-fbc4-0eb6-3537d8032577@linux.ibm.com>
Subject: Re: [PATCH v2 1/2] s390/kvm: extend kvm_s390_shadow_fault to return
 entry pointer
Message-ID: <264deb2a-a86e-79e3-9db1-ecfe265a6a10@linux.ibm.com>
Date:   Thu, 4 Feb 2021 18:05:15 +0100
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On 2/4/21 5:34 PM, Janosch Frank 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?
> 
> 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.
> 
>>  		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

You use it for pei only, right?

> 
>>   *
>>   * 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 ?
> 
>> +		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

Ok after a second pass that's not what's going on here.
Those basically directly correspond to the MVPG PEI indication bits, right?

Do we also need to consider bit 63?

> 
>> +#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;
>>  }
>>  
>>
>