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

Claudio Imbrenda
2021-02-05T12:24:33Z

On Thu, 4 Feb 2021 18:05:15 +0100
Janosch Frank <frankja@linux.ibm.com> wrote:

> 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?

yes

> >
> >> *
> >> * 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?

yes :)

> Do we also need to consider bit 63?

no, that can only happen if a specific SIE feature is used, which KVM
neither uses nor supports for VSIE, so it cannot happen

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