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KVM: s390: Remove non-atomic dat_crstep_xchg()

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In practice dat_crstep_xchg() is racy and hard to use correctly. Simply
remove it and replace its uses with dat_crstep_xchg_atomic().

This solves some actual races that lead to system hangs / crashes.

Opportunistically fix an alignment issue in _gmap_crstep_xchg_atomic().

Fixes: 589071eaaa ("KVM: s390: KVM page table management functions: clear and replace")
Fixes: 94fd9b16cc ("KVM: s390: KVM page table management functions: lifecycle management")
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
This commit is contained in:
Claudio Imbrenda
2026-03-26 14:17:11 +01:00
parent 0f54755343
commit b827ef02f4
5 changed files with 99 additions and 96 deletions
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51
arch/s390/kvm/dat.c
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@@ -134,32 +134,6 @@ int dat_set_asce_limit(struct kvm_s390_mmu_cache *mc, union asce *asce, int newt
return 0;
}
/**
* dat_crstep_xchg() - Exchange a gmap CRSTE with another.
* @crstep: Pointer to the CRST entry
* @new: Replacement entry.
* @gfn: The affected guest address.
* @asce: The ASCE of the address space.
*
* Context: This function is assumed to be called with kvm->mmu_lock held.
*/
void dat_crstep_xchg(union crste *crstep, union crste new, gfn_t gfn, union asce asce)
{
if (crstep->h.i) {
WRITE_ONCE(*crstep, new);
return;
} else if (cpu_has_edat2()) {
crdte_crste(crstep, *crstep, new, gfn, asce);
return;
}
if (machine_has_tlb_guest())
idte_crste(crstep, gfn, IDTE_GUEST_ASCE, asce, IDTE_GLOBAL);
else
idte_crste(crstep, gfn, 0, NULL_ASCE, IDTE_GLOBAL);
WRITE_ONCE(*crstep, new);
}
/**
* dat_crstep_xchg_atomic() - Atomically exchange a gmap CRSTE with another.
* @crstep: Pointer to the CRST entry.
@@ -175,8 +149,8 @@ void dat_crstep_xchg(union crste *crstep, union crste new, gfn_t gfn, union asce
*
* Return: %true if the exchange was successful.
*/
bool dat_crstep_xchg_atomic(union crste *crstep, union crste old, union crste new, gfn_t gfn,
union asce asce)
bool __must_check dat_crstep_xchg_atomic(union crste *crstep, union crste old, union crste new,
gfn_t gfn, union asce asce)
{
if (old.h.i)
return arch_try_cmpxchg((long *)crstep, &old.val, new.val);
@@ -894,7 +868,8 @@ static long _dat_slot_crste(union crste *crstep, gfn_t gfn, gfn_t next, struct d
/* This table entry needs to be updated. */
if (walk->start <= gfn && walk->end >= next) {
dat_crstep_xchg_atomic(crstep, crste, new_crste, gfn, walk->asce);
if (!dat_crstep_xchg_atomic(crstep, crste, new_crste, gfn, walk->asce))
return -EINVAL;
/* A lower level table was present, needs to be freed. */
if (!crste.h.fc && !crste.h.i) {
if (is_pmd(crste))
@@ -1072,17 +1047,19 @@ int dat_link(struct kvm_s390_mmu_cache *mc, union asce asce, int level,
static long dat_set_pn_crste(union crste *crstep, gfn_t gfn, gfn_t next, struct dat_walk *walk)
{
union crste crste = READ_ONCE(*crstep);
union crste newcrste, oldcrste;
int *n = walk->priv;
if (!crste.h.fc || crste.h.i || crste.h.p)
return 0;
do {
oldcrste = READ_ONCE(*crstep);
if (!oldcrste.h.fc || oldcrste.h.i || oldcrste.h.p)
return 0;
if (oldcrste.s.fc1.prefix_notif)
break;
newcrste = oldcrste;
newcrste.s.fc1.prefix_notif = 1;
} while (!dat_crstep_xchg_atomic(crstep, oldcrste, newcrste, gfn, walk->asce));
*n = 2;
if (crste.s.fc1.prefix_notif)
return 0;
crste.s.fc1.prefix_notif = 1;
dat_crstep_xchg(crstep, crste, gfn, walk->asce);
return 0;
}