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Wed, 4 Nov 2026 08:56:54 +0000 (GMT) Received: from [9.123.5.65] (unknown [9.123.5.65]) by smtpav03.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 4 Nov 2026 08:56:54 +0000 (GMT) Message-ID: <5bd7e8e9-3614-4006-a3d7-a51416ba5507@linux.ibm.com> Date: Wed, 4 Nov 2026 14:26:53 +0530 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 03/23] KVM: PPC: Flush/zap all memslots on kvm_arch_flush_shadow_all() To: Sean Christopherson , Madhavan Srinivasan , Paolo Bonzini Cc: Nicholas Piggin , linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Jim Mattson , James Houghton , Chris Mason References: <20261030212112.2598640-1-seanjc@google.com> <20261030212112.2598640-4-seanjc@google.com> Content-Language: en-US From: Narayana Murty N In-Reply-To: <20261030212112.2598640-4-seanjc@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-ORIG-GUID: D3HtbIrHYhFBVkH1Qk3wWusLux_I87WB X-Proofpoint-Spam-Info: AW1haW4tMjYxMTA0MDAzNCBTYWx0ZWRfX+75I8chF9UB1 cZ5RrnTSgZK+fW7yAb1FBW2kbxEDnxzKKm7KoFykscUKCm96SAL2vDM8XvDhAJsxzUTSFaYQ4uh RkruX2BfqtdJJfB503dMEyI5HDd/QU4= X-Authority-Analysis: v=2.4 cv=LokHWXdc c=1 sm=1 tr=0 ts=6aeaf35b cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=zJRp6_cAMcgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VwQbUJbxAAAA:8 a=1XWaLZrsAAAA:8 a=1QS-1g0Vr6wPOSXTiQ0A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMTA0MDAzNCBTYWx0ZWRfX4eN8xeQe6Zf3 ywbSZRXK9eMRl41agjGOMGmBmcZMIuf1c/GWQqDLHoTCm5GKkwFkjM2+aViHgMBVIGDMXyBt94u /5z4DAc3/evePjhod1tLEDxdchMzSy6epOlo+4dKGjO8g88sDgslDYx7lNKts5jO4ZlNdvuaQZP waBEWWwaFU8yswTLM4sEdY2DrBobeCJ/fjcIMNT1gjU4BmcRKYrcVlaY8OIg1z2aUfjydnA82AU nFIi/RCq4xt6rIPr62l0wWE+NgkO5HyU6aHYIMGwc1oQ1qqKUZQAem7Ugv8ZffPGihxRDTDqdDD 89b8ZEX9HB4TDUc3uhY1e+uTIxt13vMvmsAj4JyF+c1gFG9CCCJADpFmxTXkvKvC0rlkodc47BF 6c1b/b65727gRzZfde/SwMKxPPDqlfR8uO4R2RTaC+ZtDLPnQmSeZCZ68q5cDy+3mvLGBVv5kqC umz9a3kyq1vcMPzuUjg== X-Proofpoint-GUID: Ay8acS_dMbzIo1IyKYWuxL5J_zhW18KV X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.138,FMLib:17.12.100.49 definitions=2026-11-04_02,2026-11-03_04,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 lowpriorityscore=0 clxscore=1011 impostorscore=0 priorityscore=1501 suspectscore=0 phishscore=0 malwarescore=0 bulkscore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2610300000 definitions=main-2611040034 Hi Sean, On 31/10/26 2:50 AM, Sean Christopherson wrote: > Flush/zap every memslot in kvm_arch_flush_shadow_all(), i.e. when the > owning userspace process is exiting, as KVM must ensure all associated > memory is unmapped from the guest. > > Cc: stable@vger.kernel.org > Signed-off-by: Sean Christopherson > --- > arch/powerpc/include/asm/kvm_host.h | 1 - > arch/powerpc/kvm/powerpc.c | 11 +++++++++++ > 2 files changed, 11 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h > index 708a32f89776..50a42f80e5f1 100644 > --- a/arch/powerpc/include/asm/kvm_host.h > +++ b/arch/powerpc/include/asm/kvm_host.h > @@ -910,7 +910,6 @@ struct kvm_vcpu_arch { > #define __KVM_HAVE_CREATE_DEVICE > > static inline void kvm_arch_memslots_updated(struct kvm *kvm, u64 gen) {} > -static inline void kvm_arch_flush_shadow_all(struct kvm *kvm) {} > static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} > static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} > > diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c > index 9194cf492d1c..9e9d0865c2f6 100644 > --- a/arch/powerpc/kvm/powerpc.c > +++ b/arch/powerpc/kvm/powerpc.c > @@ -764,6 +764,17 @@ void kvm_arch_commit_memory_region(struct kvm *kvm, > kvmppc_core_commit_memory_region(kvm, old, new, change); > } > > +void kvm_arch_flush_shadow_all(struct kvm *kvm) > +{ > + struct kvm_memory_slot *slot; > + struct kvm_memslots *slots; > + int bkt; > + > + slots = kvm_memslots(kvm); > + kvm_for_each_memslot(slot, bkt, slots) > + kvmppc_core_flush_memslot(kvm, slot); For Book3S HV/hash, I am not sure the existing flush_memslot helper can be used on an active memslot like this. The normal memslot invalidation path seems to deliberately establish the opposite ordering. kvm_invalidate_memslot() first installs an INVALID slot and makes it active: invalid_slot->flags |= KVM_MEMSLOT_INVALID; kvm_replace_memslot(kvm, old, invalid_slot); kvm_swap_active_memslots(kvm, old->as_id); and only then does kvm_arch_flush_shadow_memslot(kvm, old);. The comment there explicitly states: /* * From this point no new shadow pages pointing to a deleted, * or moved, memslot will be created. */ Similarly, kvmppc_core_flush_memslot_hv() in arch/powerpc/kvm/book3s_64_mmu_hv.c relies on the memslot already being invalid when testing KVMPPC_RMAP_PRESENT without locking, as no new HPTEs can be created. However, kvm_arch_flush_shadow_all() in arch/powerpc/kvm/powerpc.c now invokes the same helper while walking active memslots. Is there any serialization in the mmu_notifier.release() path that provides the same guarantee against new HPTE creation? Otherwise, couldn't an H_ENTER or fault path create a new HPTE while the rmap is being scanned, or after it has already been examined? > +} > + > void kvm_arch_flush_shadow_memslot(struct kvm *kvm, > struct kvm_memory_slot *slot) > { Thanks, Narayana Murty.