Re: [PATCH v2 1/2] s390/kvm: extend kvm_s390_shadow_fault to return entry pointer

Janosch Frank
2021-02-05T22:50:21Z

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.

>
>>> *
>>> * 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;
>>> }
>>>
>>>
>>
>