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Tue, 19 May 2026 15:01:17 +0000 (GMT) Received: from p-imbrenda.ibmuc.com (unknown [9.111.4.60]) by smtpav03.fra02v.mail.ibm.com (Postfix) with ESMTP; Tue, 19 May 2026 15:01:17 +0000 (GMT) From: Claudio Imbrenda To: linux-kernel@vger.kernel.org Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org, borntraeger@de.ibm.com, frankja@linux.ibm.com, david@kernel.org, seiden@linux.ibm.com, nrb@linux.ibm.com, schlameuss@linux.ibm.com, gra@linux.ibm.com Subject: [PATCH v3 3/5] KVM: s390: vsie: Fix unshadowing logic Date: Tue, 19 May 2026 17:01:12 +0200 Message-ID: <20260519150114.264309-4-imbrenda@linux.ibm.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260519150114.264309-1-imbrenda@linux.ibm.com> References: <20260519150114.264309-1-imbrenda@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTE5MDE0NSBTYWx0ZWRfX9BMaFlfY+TOD DAAa5MXOm7y6Lq21u8C1h8cFvxm6KJbmo0CPimfhBAxP6IdYE2eiMok36ij/Lj1IHkSG+vwt4kK 84geoWJol4i7GQkBJExEEJ6AzGi+Qnqo5OPNMOEkQwp7YMUrfAHfil3vBMEJy+qF+fIUe8LGIuO +fZM7euo/NDOg5tKHw0TPIo29f22gOiHShTm7CrK6P0og8blFKKX23pv01CWaA4RAooht1qmM4S VbLp4emj58NY4l/3f3hnL2kKPCf2dAfp/Slvzpt8mfKo4odKyF37ekWaKC3mfOsZvKhY3NNnJcj eOPedlIqwbz0uD4u2quqMnIcAODI1NzTd1Di81bMg7SfFqWApxwxoeQATrilm62pz4dwR5VLdKA aI5guXglISM/nvz1anDOGMGd7bhIky8RzsxdkoTS0wEs7b2AhiXorqGR/rXtDR8a3r6OxbkqlTe e8u4LWU4kLIjDL0tXpA== X-Authority-Analysis: v=2.4 cv=BNuDalQG c=1 sm=1 tr=0 ts=6a0c7b45 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VnNF1IyMAAAA:8 a=HUs3gJRqiL1-pXx69t4A:9 X-Proofpoint-ORIG-GUID: anbZT4MMj7CjRIHOmWOcWLJ8BC-BAqar X-Proofpoint-GUID: anbZT4MMj7CjRIHOmWOcWLJ8BC-BAqar X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-05-19_04,2026-05-18_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 priorityscore=1501 malwarescore=0 impostorscore=0 suspectscore=0 lowpriorityscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2605130000 definitions=main-2605190145 In some cases (i.e. under extreme memory pressure on the host), attempting to shadow memory will result in the same memory being unshadowed, causing a loop. Add a PGSTE bit to distinguish between shadowed memory and shadowed DAT tables, fix the unshadowing logic in _gmap_ptep_xchg() to prevent unnecessary unshadowing and perform better checks. Also fix the unshadowing logic in _gmap_crstep_xchg_atomic() which did not unshadow properly when the large page would become unprotected. Opportunistically add a check in gmap_protect_rmap() to make sure it won't be called with level == TABLE_TYPE_PAGE_TABLE. Signed-off-by: Claudio Imbrenda Fixes: a2c17f9270cc ("KVM: s390: New gmap code") --- arch/s390/kvm/dat.c | 1 + arch/s390/kvm/dat.h | 3 ++- arch/s390/kvm/gaccess.c | 1 + arch/s390/kvm/gmap.c | 3 ++- arch/s390/kvm/gmap.h | 60 ++++++++++++++++++++++++++++++++++++++--- 5 files changed, 63 insertions(+), 5 deletions(-) diff --git a/arch/s390/kvm/dat.c b/arch/s390/kvm/dat.c index 7b8d70fe406d..4a41c0247ffa 100644 --- a/arch/s390/kvm/dat.c +++ b/arch/s390/kvm/dat.c @@ -267,6 +267,7 @@ static int dat_split_ste(struct kvm_s390_mmu_cache *mc, union pmd *pmdp, gfn_t g /* No need to take locks as the page table is not installed yet. */ pgste_init.prefix_notif = old.s.fc1.prefix_notif; pgste_init.vsie_notif = old.s.fc1.vsie_notif; + pgste_init.vsie_gmem = old.s.fc1.vsie_notif; pgste_init.pcl = uses_skeys && init.h.i; dat_init_pgstes(pt, pgste_init.val); } else { diff --git a/arch/s390/kvm/dat.h b/arch/s390/kvm/dat.h index 8f8278c44879..873e13ac5a27 100644 --- a/arch/s390/kvm/dat.h +++ b/arch/s390/kvm/dat.h @@ -145,7 +145,8 @@ union pgste { unsigned long cmma_d : 1; /* Dirty flag for CMMA bits */ unsigned long prefix_notif : 1; /* Guest prefix invalidation notification */ unsigned long vsie_notif : 1; /* Referenced in a shadow table */ - unsigned long : 5; + unsigned long vsie_gmem : 1; /* Contains nested guest memory */ + unsigned long : 4; unsigned long : 8; }; struct { diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c index b07accd19618..4f8d5592c9a9 100644 --- a/arch/s390/kvm/gaccess.c +++ b/arch/s390/kvm/gaccess.c @@ -1445,6 +1445,7 @@ static int _do_shadow_pte(struct gmap *sg, gpa_t raddr, union pte *ptep_h, union } else { pgste = _gmap_ptep_xchg(sg->parent, ptep_h, newpte, pgste, f->gfn, false); pgste.vsie_notif = 1; + pgste.vsie_gmem = 1; } pgste_set_unlock(ptep_h, pgste); if (rc) diff --git a/arch/s390/kvm/gmap.c b/arch/s390/kvm/gmap.c index 10c98c8cc1d8..8cff0cf5ce24 100644 --- a/arch/s390/kvm/gmap.c +++ b/arch/s390/kvm/gmap.c @@ -1031,7 +1031,8 @@ int gmap_protect_rmap(struct kvm_s390_mmu_cache *mc, struct gmap *sg, gfn_t p_gf union pte pte; int flags, rc; - KVM_BUG_ON(!is_shadow(sg), sg->kvm); + if (KVM_BUG_ON(!is_shadow(sg) || level <= TABLE_TYPE_PAGE_TABLE, sg->kvm)) + return -EINVAL; lockdep_assert_held(&sg->parent->children_lock); flags = DAT_WALK_SPLIT_ALLOC | (uses_skeys(sg->parent) ? DAT_WALK_USES_SKEYS : 0); diff --git a/arch/s390/kvm/gmap.h b/arch/s390/kvm/gmap.h index 96ee1395a592..6e51ec6066b4 100644 --- a/arch/s390/kvm/gmap.h +++ b/arch/s390/kvm/gmap.h @@ -167,6 +167,36 @@ static inline bool gmap_unmap_prefix(struct gmap *gmap, gfn_t gfn, gfn_t end) return _gmap_unmap_prefix(gmap, gfn, end, false); } +/** + * pte_needs_unshadow() -- Check if the pte operations triggers unshadowing. + * @oldpte: the previous value for the guest pte. + * @newpte: the new pte being set. + * @pgste: the pgste for the pte entry. + * + * If the pgste.vsie_notif bit is not set, return false: the page is not + * involved in vsie and thus should not trigger an unshadow operation. + * + * If the pgste.vsie_gmem bit is set, this pte represents shadowed guest + * memory. The access rights on g3's memory should be synchronized with g1's + * and g2's. Therefore unshadowing is triggered if the new and old pte + * differ in protection, or if the new pte is invalid. + * + * If the pgste.vsie_gmem bit is not set, this pte maps the g2 dat tables + * for g3. If the entry becomes writable or absent, it becomes impossible to + * guarantee that the shadow mapping will match g2's mapping. In that case, + * trigger an unshadow event. + * + * Return: true if an unshadow event should be triggered, otherwise false. + */ +static inline bool pte_needs_unshadow(union pte oldpte, union pte newpte, union pgste pgste) +{ + if (!pgste.vsie_notif) + return false; + if (pgste.vsie_gmem) + return (oldpte.h.p != newpte.h.p) || newpte.h.i; + return !newpte.h.p || !newpte.s.pr; +} + static inline union pgste _gmap_ptep_xchg(struct gmap *gmap, union pte *ptep, union pte newpte, union pgste pgste, gfn_t gfn, bool needs_lock) { @@ -180,8 +210,9 @@ static inline union pgste _gmap_ptep_xchg(struct gmap *gmap, union pte *ptep, un pgste.prefix_notif = 0; gmap_unmap_prefix(gmap, gfn, gfn + 1); } - if (pgste.vsie_notif && (ptep->h.p != newpte.h.p || newpte.h.i)) { + if (pte_needs_unshadow(*ptep, newpte, pgste)) { pgste.vsie_notif = 0; + pgste.vsie_gmem = 0; if (needs_lock) gmap_handle_vsie_unshadow_event(gmap, gfn); else @@ -198,6 +229,30 @@ static inline union pgste gmap_ptep_xchg(struct gmap *gmap, union pte *ptep, uni return _gmap_ptep_xchg(gmap, ptep, newpte, pgste, gfn, true); } +/** + * crste_needs_unshadow() -- Check if the crste operations triggers unshadowing. + * @oldcrste: the previous value for the crste. + * @newcrste: the new value for the crste. + * + * If the old crste did not have the vsie_notif bit set, return false: the + * page is not involved in vsie and thus should not trigger an unshadow + * operation. Conversely, if the bit is set, it can only be g3 memory, since + * dat tables are never mapped using large pages. + * + * Similar to the pgste.vsie_gmem case of pte_needs_unshadow(), if the + * protection bit is changing or the new page is invalid, trigger an + * unshadow event. Also trigger an unshadow event if the new crste does not + * have the vsie_notif bit set. + * + * Return: true if an unshadow event should be triggered, otherwise false. + */ +static inline bool crste_needs_unshadow(union crste oldcrste, union crste newcrste) +{ + if (!oldcrste.s.fc1.vsie_notif) + return false; + return (newcrste.h.p != oldcrste.h.p) || newcrste.h.i || !newcrste.s.fc1.vsie_notif; +} + static inline bool __must_check _gmap_crstep_xchg_atomic(struct gmap *gmap, union crste *crstep, union crste oldcrste, union crste newcrste, gfn_t gfn, bool needs_lock) @@ -216,8 +271,7 @@ static inline bool __must_check _gmap_crstep_xchg_atomic(struct gmap *gmap, unio newcrste.s.fc1.prefix_notif = 0; gmap_unmap_prefix(gmap, gfn, gfn + align); } - if (crste_leaf(oldcrste) && oldcrste.s.fc1.vsie_notif && - (newcrste.h.p || newcrste.h.i || !newcrste.s.fc1.vsie_notif)) { + if (crste_leaf(oldcrste) && crste_needs_unshadow(oldcrste, newcrste)) { newcrste.s.fc1.vsie_notif = 0; if (needs_lock) gmap_handle_vsie_unshadow_event(gmap, gfn); -- 2.54.0