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

Claudio Imbrenda
2021-02-05T16:23:58Z

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;
> >>> }
> >>>
> >>>
> >>
> >
>