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AJvYcCVB9Vt9Dri8wYGbU4zkKB4rm8qapKD/04QaFu20wIgADI+MfuY+VTueg3l2VHBlfkgKiMK0jh/6IBmQglMF@vger.kernel.org X-Gm-Message-State: AOJu0Yy6+ziYKuaMeY70c7vqW0dBbjQyRnyVXiMMtsx7dOG5HnIOdad3 xpdFWJge+BvdlinZajU+QHw9ZxB1TSNZWD29GG9TCBVIO2cRE79EvRJ78yASNus56JN272TRBbH RiBnslg== X-Google-Smtp-Source: AGHT+IHbAz/eKQpxYLnv3UzRDiNfzFQyWZ03GI8G+wp5sD4kBBYyUq+g8Y0WEpcjXQKRT5uv4bipYXGp6JQ= X-Received: from pjbsf1.prod.google.com ([2002:a17:90b:51c1:b0:2e0:915d:d594]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:514e:b0:312:25dd:1c86 with SMTP id 98e67ed59e1d1-31e778f7879mr4767541a91.18.1753464276017; Fri, 25 Jul 2025 10:24:36 -0700 (PDT) Date: Fri, 25 Jul 2025 10:24:34 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250723104714.1674617-1-tabba@google.com> <20250723104714.1674617-15-tabba@google.com> <1ff6a90a-3e03-4104-9833-4b07bb84831f@intel.com> Message-ID: Subject: Re: [PATCH v16 14/22] KVM: x86/mmu: Enforce guest_memfd's max order when recovering hugepages From: Sean Christopherson To: Ackerley Tng Cc: Xiaoyao Li , Fuad Tabba , kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, kvmarm@lists.linux.dev, pbonzini@redhat.com, chenhuacai@kernel.org, mpe@ellerman.id.au, anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, viro@zeniv.linux.org.uk, brauner@kernel.org, willy@infradead.org, akpm@linux-foundation.org, yilun.xu@intel.com, chao.p.peng@linux.intel.com, jarkko@kernel.org, amoorthy@google.com, dmatlack@google.com, isaku.yamahata@intel.com, mic@digikod.net, vbabka@suse.cz, vannapurve@google.com, mail@maciej.szmigiero.name, david@redhat.com, michael.roth@amd.com, wei.w.wang@intel.com, liam.merwick@oracle.com, isaku.yamahata@gmail.com, kirill.shutemov@linux.intel.com, suzuki.poulose@arm.com, steven.price@arm.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_tsoni@quicinc.com, quic_svaddagi@quicinc.com, quic_cvanscha@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, catalin.marinas@arm.com, james.morse@arm.com, yuzenghui@huawei.com, oliver.upton@linux.dev, maz@kernel.org, will@kernel.org, qperret@google.com, keirf@google.com, roypat@amazon.co.uk, shuah@kernel.org, hch@infradead.org, jgg@nvidia.com, rientjes@google.com, jhubbard@nvidia.com, fvdl@google.com, hughd@google.com, jthoughton@google.com, peterx@redhat.com, pankaj.gupta@amd.com, ira.weiny@intel.com Content-Type: text/plain; charset="us-ascii" On Fri, Jul 25, 2025, Sean Christopherson wrote: > On Thu, Jul 24, 2025, Ackerley Tng wrote: > I also don't want to effectively speculatively add kvm_gmem_mapping_order() or > expand kvm_gmem_get_pfn(), e.g. to say "no create", so what if we just do this? > > /* For faults, use the gmem information that was resolved earlier. */ > if (fault) { > pfn = fault->pfn; > max_level = fault->max_level; > } else { > /* TODO: Call into guest_memfd once hugepages are supported. */ Aha! Even better, we can full on WARN: WARN_ONCE(1, "Get pfn+order from guest_memfd"); Because guest_memfd doesn't yet support dirty logging: /* Dirty logging private memory is not currently supported. */ if (mem->flags & KVM_MEM_GUEST_MEMFD) valid_flags &= ~KVM_MEM_LOG_DIRTY_PAGES; which kills off the kvm_mmu_recover_huge_pages() call from kvm_mmu_slot_apply_flags(). And if KVM ever supports in-place recover for kvm_recover_nx_huge_pages() (which is doubtful given that mitigation shouldn't be required going forward), lack of hugepage support means any guest_memfd-based shadow page can't be a possible NX hugepage.