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KVM: s390: Track page size in struct guest_fault

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Until now, the members of struct guest_fault are always accessed while
holding the required locks, and thus the ptep and crstep pointers can
be dereferenced safely.

There will be some new cases where callers of kvm_s390_faultin_gfn()
need to know the size of the page used to solve the fault, at which
point no locks are held anymore, and dereferencing the crstep field
is not possible.

Introduce a new crste_region3 flag for struct guest_fault to indicate
whether the crstep used to solve the fault was a region 3 entry with FC=1
(large pud).

This allows to disambiguate all three possible scenarios:
* If ptep is not NULL, the fault was solved with a pte.
* If ptep is NULL and crste_region3 is 0, a segment entry with FC=1
  (large pmd) was used.
* If ptep is NULL and crste_region3 is 1, a region 3 entry with FC=1
  (large pud) was used.

Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-ID: <20260527144358.186359-2-imbrenda@linux.ibm.com>
This commit is contained in:
Claudio Imbrenda 2026-05-27 16:43:54 +02:00
parent 7fd2df204f
commit 499d2e4b75
2 changed files with 3 additions and 0 deletions
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1
arch/s390/kvm/dat.h
View File

@ -500,6 +500,7 @@ struct guest_fault {
bool write_attempt; /* Write access attempted */
bool attempt_pfault; /* Attempt a pfault first */
bool valid; /* This entry contains valid data */
bool crste_region3; /* Whether crstep refers to a region3 entry */
void (*callback)(struct guest_fault *f);
void *priv;
};

2
arch/s390/kvm/gmap.c
View File

@ -531,6 +531,7 @@ static int gmap_handle_minor_crste_fault(struct gmap *gmap, struct guest_fault *
f->pfn = PHYS_PFN(large_crste_to_phys(oldcrste, f->gfn));
f->writable = oldcrste.s.fc1.w;
f->crste_region3 = is_pud(oldcrste);
/* Appropriate permissions already (race with another handler), nothing to do. */
if (!oldcrste.h.i && !(f->write_attempt && oldcrste.h.p))
return 0;
@ -690,6 +691,7 @@ static int _gmap_link(struct kvm_s390_mmu_cache *mc, struct gmap *gmap, int leve
if (oldval.val != _CRSTE_EMPTY(oldval.h.tt).val &&
crste_origin_large(oldval) != crste_origin_large(newval))
return -EAGAIN;
f->crste_region3 = is_pud(newval);
} while (!gmap_crstep_xchg_atomic(gmap, f->crstep, oldval, newval, f->gfn));
if (f->callback)
f->callback(f);