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Tue, 29 Jul 2025 15:55:55 -0700 (PDT) Date: Tue, 29 Jul 2025 15:54:45 -0700 In-Reply-To: <20250729225455.670324-1-seanjc@google.com> Mime-Version: 1.0 References: <20250729225455.670324-1-seanjc@google.com> X-Mailer: git-send-email 2.50.1.552.g942d659e1b-goog Message-ID: <20250729225455.670324-15-seanjc@google.com> Subject: [PATCH v17 14/24] KVM: x86/mmu: Enforce guest_memfd's max order when recovering hugepages From: Sean Christopherson To: Paolo Bonzini , Marc Zyngier , Oliver Upton , Sean Christopherson Cc: kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, Ira Weiny , Gavin Shan , Shivank Garg , Vlastimil Babka , Xiaoyao Li , David Hildenbrand , Fuad Tabba , Ackerley Tng , Tao Chan , James Houghton Content-Type: text/plain; charset="UTF-8" X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250729_155557_006818_0380BAC0 X-CRM114-Status: GOOD ( 20.64 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Sean Christopherson Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Rework kvm_mmu_max_mapping_level() to provide the plumbing to consult guest_memfd (and relevant vendor code) when recovering hugepages, e.g. after disabling live migration. The flaw has existed since guest_memfd was originally added, but has gone unnoticed due to lack of guest_memfd support for hugepages or dirty logging. Don't actually call into guest_memfd at this time, as it's unclear as to what the API should be. Ideally, KVM would simply use kvm_gmem_get_pfn(), but invoking kvm_gmem_get_pfn() would lead to sleeping in atomic context if guest_memfd needed to allocate memory (mmu_lock is held). Luckily, the path isn't actually reachable, so just add a TODO and WARN to ensure the functionality is added alongisde guest_memfd hugepage support, and punt the guest_memfd API design question to the future. Note, calling kvm_mem_is_private() in the non-fault path is safe, so long as mmu_lock is held, as hugepage recovery operates on shadow-present SPTEs, i.e. calling kvm_mmu_max_mapping_level() with @fault=NULL is mutually exclusive with kvm_vm_set_mem_attributes() changing the PRIVATE attribute of the gfn. Signed-off-by: Sean Christopherson --- arch/x86/kvm/mmu/mmu.c | 82 +++++++++++++++++++-------------- arch/x86/kvm/mmu/mmu_internal.h | 2 +- arch/x86/kvm/mmu/tdp_mmu.c | 2 +- 3 files changed, 49 insertions(+), 37 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 20dd9f64156e..61eb9f723675 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -3302,31 +3302,54 @@ static u8 kvm_max_level_for_order(int order) return PG_LEVEL_4K; } -static u8 kvm_max_private_mapping_level(struct kvm *kvm, kvm_pfn_t pfn, - u8 max_level, int gmem_order) +static u8 kvm_max_private_mapping_level(struct kvm *kvm, struct kvm_page_fault *fault, + const struct kvm_memory_slot *slot, gfn_t gfn) { - u8 req_max_level; + u8 max_level, coco_level; + kvm_pfn_t pfn; - if (max_level == PG_LEVEL_4K) - return PG_LEVEL_4K; + /* 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. */ + WARN_ONCE(1, "Get pfn+order from guest_memfd"); + pfn = KVM_PFN_ERR_FAULT; + max_level = PG_LEVEL_4K; + } - max_level = min(kvm_max_level_for_order(gmem_order), max_level); if (max_level == PG_LEVEL_4K) - return PG_LEVEL_4K; + return max_level; - req_max_level = kvm_x86_call(gmem_max_mapping_level)(kvm, pfn); - if (req_max_level) - max_level = min(max_level, req_max_level); + /* + * CoCo may influence the max mapping level, e.g. due to RMP or S-EPT + * restrictions. A return of '0' means "no additional restrictions", to + * allow for using an optional "ret0" static call. + */ + coco_level = kvm_x86_call(gmem_max_mapping_level)(kvm, pfn); + if (coco_level) + max_level = min(max_level, coco_level); return max_level; } -static int __kvm_mmu_max_mapping_level(struct kvm *kvm, - const struct kvm_memory_slot *slot, - gfn_t gfn, int max_level, bool is_private) +int kvm_mmu_max_mapping_level(struct kvm *kvm, struct kvm_page_fault *fault, + const struct kvm_memory_slot *slot, gfn_t gfn) { struct kvm_lpage_info *linfo; - int host_level; + int host_level, max_level; + bool is_private; + + lockdep_assert_held(&kvm->mmu_lock); + + if (fault) { + max_level = fault->max_level; + is_private = fault->is_private; + } else { + max_level = PG_LEVEL_NUM; + is_private = kvm_mem_is_private(kvm, gfn); + } max_level = min(max_level, max_huge_page_level); for ( ; max_level > PG_LEVEL_4K; max_level--) { @@ -3335,25 +3358,16 @@ static int __kvm_mmu_max_mapping_level(struct kvm *kvm, break; } + if (max_level == PG_LEVEL_4K) + return PG_LEVEL_4K; + if (is_private) - return max_level; - - if (max_level == PG_LEVEL_4K) - return PG_LEVEL_4K; - - host_level = host_pfn_mapping_level(kvm, gfn, slot); + host_level = kvm_max_private_mapping_level(kvm, fault, slot, gfn); + else + host_level = host_pfn_mapping_level(kvm, gfn, slot); return min(host_level, max_level); } -int kvm_mmu_max_mapping_level(struct kvm *kvm, - const struct kvm_memory_slot *slot, gfn_t gfn) -{ - bool is_private = kvm_slot_has_gmem(slot) && - kvm_mem_is_private(kvm, gfn); - - return __kvm_mmu_max_mapping_level(kvm, slot, gfn, PG_LEVEL_NUM, is_private); -} - void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault) { struct kvm_memory_slot *slot = fault->slot; @@ -3374,9 +3388,8 @@ void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault * Enforce the iTLB multihit workaround after capturing the requested * level, which will be used to do precise, accurate accounting. */ - fault->req_level = __kvm_mmu_max_mapping_level(vcpu->kvm, slot, - fault->gfn, fault->max_level, - fault->is_private); + fault->req_level = kvm_mmu_max_mapping_level(vcpu->kvm, fault, + fault->slot, fault->gfn); if (fault->req_level == PG_LEVEL_4K || fault->huge_page_disallowed) return; @@ -4564,8 +4577,7 @@ static int kvm_mmu_faultin_pfn_private(struct kvm_vcpu *vcpu, } fault->map_writable = !(fault->slot->flags & KVM_MEM_READONLY); - fault->max_level = kvm_max_private_mapping_level(vcpu->kvm, fault->pfn, - fault->max_level, max_order); + fault->max_level = kvm_max_level_for_order(max_order); return RET_PF_CONTINUE; } @@ -7165,7 +7177,7 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm, * mapping if the indirect sp has level = 1. */ if (sp->role.direct && - sp->role.level < kvm_mmu_max_mapping_level(kvm, slot, sp->gfn)) { + sp->role.level < kvm_mmu_max_mapping_level(kvm, NULL, slot, sp->gfn)) { kvm_zap_one_rmap_spte(kvm, rmap_head, sptep); if (kvm_available_flush_remote_tlbs_range()) diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h index 65f3c89d7c5d..b776be783a2f 100644 --- a/arch/x86/kvm/mmu/mmu_internal.h +++ b/arch/x86/kvm/mmu/mmu_internal.h @@ -411,7 +411,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, return r; } -int kvm_mmu_max_mapping_level(struct kvm *kvm, +int kvm_mmu_max_mapping_level(struct kvm *kvm, struct kvm_page_fault *fault, const struct kvm_memory_slot *slot, gfn_t gfn); void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault); void disallowed_hugepage_adjust(struct kvm_page_fault *fault, u64 spte, int cur_level); diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index 7f3d7229b2c1..740cb06accdb 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -1813,7 +1813,7 @@ static void recover_huge_pages_range(struct kvm *kvm, if (iter.gfn < start || iter.gfn >= end) continue; - max_mapping_level = kvm_mmu_max_mapping_level(kvm, slot, iter.gfn); + max_mapping_level = kvm_mmu_max_mapping_level(kvm, NULL, slot, iter.gfn); if (max_mapping_level < iter.level) continue; -- 2.50.1.552.g942d659e1b-goog