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[34.77.69.137]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49508728019sm163467455e9.5.2026.07.15.10.56.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Jul 2026 10:56:36 -0700 (PDT) Date: Wed, 15 Jul 2026 18:56:33 +0100 From: Vincent Donnefort To: Mostafa Saleh Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev, iommu@lists.linux.dev, catalin.marinas@arm.com, will@kernel.org, maz@kernel.org, oliver.upton@linux.dev, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, joro@8bytes.org, jgg@ziepe.ca, mark.rutland@arm.com, qperret@google.com, tabba@google.com, sebastianene@google.com, keirf@google.com Subject: Re: [PATCH v7 07/24] KVM: arm64: iommu: Shadow host stage-2 page table Message-ID: References: <20260715115906.2664882-1-smostafa@google.com> <20260715115906.2664882-8-smostafa@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260715115906.2664882-8-smostafa@google.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260715_105640_499699_69A98CEE X-CRM114-Status: GOOD ( 46.84 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Jul 15, 2026 at 11:58:48AM +0000, Mostafa Saleh wrote: > Create a page-table for the IOMMU that shadows the host CPU stage-2 > to establish DMA isolation. > > An initial snapshot is created after the driver init, then > on every permission change a callback would be called for > the IOMMU driver to update the page table. > > There are 3 different ways to add the callback: > 1) In the high level memory transitions: (__pkvm_host_donate_hyp(), > __pkvm_host_donate_guest()... > > 2) In Lower level functions covering all transitions > - host_stage2_set_owner_metadata_locked() which covers: > - __pkvm_host_donate_hyp() > - __pkvm_host_donate_guest() > - __pkvm_host_donate_hyp() > - __pkvm_guest_unshare_host() > - host_stage2_set_owner_locked() only for ID_HOST which covers: > - __pkvm_hyp_donate_host() > - __pkvm_host_force_reclaim_page_guest() > - __pkvm_host_reclaim_page_guest() > - __pkvm_guest_share_host() > > 3) In the lowest level function __host_update_page_state(), which > requires only one callback. However, in that case the page state > is not enough as we might need to know the old state also. > > Option #2 was implemented here. > > For some cases, an SMMUv3 may be able to share the same page-table > used with the host CPU stage-2 directly. > > However, this is too strict and requires changes to the core hypervisor > page-table code, plus it would require the hypervisor to handle IOMMU > page-faults. This can be added later as an optimization for SMMUV3. > > Signed-off-by: Mostafa Saleh > --- > arch/arm64/kvm/hyp/include/nvhe/iommu.h | 4 + > arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 1 + > arch/arm64/kvm/hyp/nvhe/iommu.c | 129 +++++++++++++++++- > arch/arm64/kvm/hyp/nvhe/mem_protect.c | 27 ++-- > 4 files changed, 145 insertions(+), 16 deletions(-) > > diff --git a/arch/arm64/kvm/hyp/include/nvhe/iommu.h b/arch/arm64/kvm/hyp/include/nvhe/iommu.h > index df3d0cc5d4db..857d7dd2ebc3 100644 > --- a/arch/arm64/kvm/hyp/include/nvhe/iommu.h > +++ b/arch/arm64/kvm/hyp/include/nvhe/iommu.h > @@ -3,11 +3,15 @@ > #define __ARM64_KVM_NVHE_IOMMU_H__ > > #include > +#include > > struct pkvm_iommu_ops { > int (*init)(void); > + int (*host_stage2_idmap)(phys_addr_t start, phys_addr_t end, int prot); > }; > > int pkvm_iommu_init(void); > > +int pkvm_iommu_host_stage2_idmap(phys_addr_t start, phys_addr_t end, > + enum kvm_pgtable_prot prot); > #endif /* __ARM64_KVM_NVHE_IOMMU_H__ */ > diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > index 51b0eb3844a9..99b821b3cf65 100644 > --- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > +++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > @@ -59,6 +59,7 @@ int __pkvm_host_test_clear_young_guest(u64 gfn, u64 nr_pages, bool mkold, struct > int __pkvm_host_mkyoung_guest(u64 gfn, struct pkvm_hyp_vcpu *vcpu); > > bool addr_is_memory(phys_addr_t phys); > + > int host_stage2_idmap_locked(phys_addr_t addr, u64 size, enum kvm_pgtable_prot prot); > int host_stage2_set_owner_locked(phys_addr_t addr, u64 size, u8 owner_id); > int kvm_host_prepare_stage2(void *pgt_pool_base); > diff --git a/arch/arm64/kvm/hyp/nvhe/iommu.c b/arch/arm64/kvm/hyp/nvhe/iommu.c > index ef456eff42d2..08009609ec59 100644 > --- a/arch/arm64/kvm/hyp/nvhe/iommu.c > +++ b/arch/arm64/kvm/hyp/nvhe/iommu.c > @@ -4,16 +4,137 @@ > * > * Copyright (C) 2022 Linaro Ltd. > */ > +#include > +#include > + > #include > +#include > +#include > > /* Only one set of ops supported */ > struct pkvm_iommu_ops *pkvm_iommu_ops; > > -int pkvm_iommu_init(void) > +/* Protected by host_mmu.lock */ > +static bool pkvm_idmap_initialized; > + > +static inline int pkvm_to_iommu_prot(enum kvm_pgtable_prot prot) > { > - /* Keep DMA isolation optional. */ > - if (!pkvm_iommu_ops || !pkvm_iommu_ops->init) > + int iommu_prot = 0; > + > + if (prot & KVM_PGTABLE_PROT_R) > + iommu_prot |= IOMMU_READ; > + if (prot & KVM_PGTABLE_PROT_W) > + iommu_prot |= IOMMU_WRITE; > + > + /* We don't understand that, might be dangerous. */ > + WARN_ON(prot & ~PKVM_HOST_MEM_PROT); > + return iommu_prot; > +} > + > +/* > + * IOMMU page tables are shadowed and not shared, that is mainly because: > + * - Possible inconsistency between IOMMU and CPU features or format. > + * - KVM relies on handling in page faults (BBM, lazy mapping). > + */ > +static int __snapshot_host_stage2(const struct kvm_pgtable_visit_ctx *ctx, > + enum kvm_pgtable_walk_flags visit) > +{ > + u64 start = ctx->addr; > + u64 block_end = ALIGN_DOWN(ctx->addr, kvm_granule_size(ctx->level)) + > + kvm_granule_size(ctx->level); nit: I believe that for more complex init like that we should just put it after the declarations. > + u64 end = min(ctx->end, block_end); > + kvm_pte_t pte = *ctx->ptep; > + bool is_memory = *(bool *)ctx->arg; > + int prot; > + > + /* > + * Keep annotated PTEs unmapped, and map everything else even lazily > + * mapped PTEs(0), as the IOMMU can't handle page faults. > + * That maps the whole address space which can be large, but that doesn't > + * use a lot of memory as it will be mostly large block (1 GB with 4kb pages) > + */ > + if (pte && !kvm_pte_valid(pte)) > return 0; > > - return pkvm_iommu_ops->init(); > + if (kvm_pte_valid(pte)) > + prot = pkvm_to_iommu_prot(kvm_pgtable_stage2_pte_prot(pte)); > + else > + prot = IOMMU_READ | IOMMU_WRITE; > + > + if (!is_memory) > + prot |= IOMMU_MMIO; > + > + return pkvm_iommu_ops->host_stage2_idmap(start, end, prot); > +} > + > +static int pkvm_iommu_snapshot_host_stage2(void) > +{ > + struct kvm_pgtable *pgt = &host_mmu.pgt; > + bool is_memory; > + struct kvm_pgtable_walker walker = { > + .cb = __snapshot_host_stage2, > + .flags = KVM_PGTABLE_WALK_LEAF, > + .arg = &is_memory, > + }; > + int ret = 0, i; > + u64 start = 0; > + > + hyp_spin_lock(&host_mmu.lock); > + for (i = 0; i < hyp_memblock_nr; i++) { > + struct memblock_region *reg = &hyp_memory[i]; > + > + if (start < reg->base) { > + is_memory = false; > + ret = kvm_pgtable_walk(pgt, start, reg->base - start, &walker); nit: You could have a helper? So is_memory isn't passed as a reference. __snapshot_host_stage2(u64 start, u64 end, bool is_memory) > + if (ret) > + goto out_unlock; > + } > + > + is_memory = true; > + ret = kvm_pgtable_walk(pgt, reg->base, reg->size, &walker); > + if (ret) > + goto out_unlock; > + > + start = reg->base + reg->size; > + } > + > + if (start < BIT(pgt->ia_bits)) { > + is_memory = false; > + ret = kvm_pgtable_walk(pgt, start, BIT(pgt->ia_bits) - start, &walker); > + if (ret) > + goto out_unlock; > + } > + > + pkvm_idmap_initialized = true; > + > +out_unlock: > + hyp_spin_unlock(&host_mmu.lock); > + return ret; > +} > + > +int pkvm_iommu_init(void) > +{ > + int ret; > + > + /* Keep DMA isolation optional. */ > + if (!pkvm_iommu_ops || !pkvm_iommu_ops->init || > + !pkvm_iommu_ops->host_stage2_idmap) > + return 0; > + > + ret = pkvm_iommu_ops->init(); > + if (ret) > + return ret; > + > + return pkvm_iommu_snapshot_host_stage2(); > +} > + > +int pkvm_iommu_host_stage2_idmap(phys_addr_t start, phys_addr_t end, > + enum kvm_pgtable_prot prot) > +{ > + hyp_assert_lock_held(&host_mmu.lock); > + > + if (!pkvm_idmap_initialized) > + return 0; > + > + return pkvm_iommu_ops->host_stage2_idmap(start, end, pkvm_to_iommu_prot(prot)); Out of curiosity, why is it "host_stage2_idmap" and not just "idmap" ? > } > diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > index d803b3dd4cb4..ce610274bda0 100644 > --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c > +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > @@ -17,6 +17,7 @@ > > #include > #include > +#include > #include > #include > #include > @@ -596,16 +597,15 @@ static int host_stage2_set_owner_metadata_locked(phys_addr_t addr, u64 size, > ret = host_stage2_try(kvm_pgtable_stage2_annotate, &host_mmu.pgt, > addr, size, &host_s2_pool, > KVM_HOST_INVALID_PTE_TYPE_DONATION, annotation); > - if (!ret) { > - /* > - * After stage2 maintenance has happened, but before the page > - * owner has changed. > - */ > - pkvm_sme_dvmsync_fw_call(); > - __host_update_page_state(addr, size, PKVM_NOPAGE); > - } > - > - return ret; > + if (ret) > + return ret; > + /* > + * After stage2 maintenance has happened, but before the page > + * owner has changed. > + */ > + pkvm_sme_dvmsync_fw_call(); > + __host_update_page_state(addr, size, PKVM_NOPAGE); > + return pkvm_iommu_host_stage2_idmap(addr, addr + size, 0); On error here the host stage-2 annotation needs to be reverted. Or just WARN_ON() here. It also probably better to do it before the page-state has changed, even if we hold the host stage-2 lock. > } > > int host_stage2_set_owner_locked(phys_addr_t addr, u64 size, u8 owner_id) > @@ -618,8 +618,10 @@ int host_stage2_set_owner_locked(phys_addr_t addr, u64 size, u8 owner_id) > return -EPERM; > > ret = host_stage2_idmap_locked(addr, size, PKVM_HOST_MEM_PROT); > - if (!ret) > - __host_update_page_state(addr, size, PKVM_PAGE_OWNED); > + if (ret) > + break; > + __host_update_page_state(addr, size, PKVM_PAGE_OWNED); > + ret = pkvm_iommu_host_stage2_idmap(addr, addr + size, PKVM_HOST_MEM_PROT); > break; > case PKVM_ID_HYP: > ret = host_stage2_set_owner_metadata_locked(addr, size, > @@ -1022,6 +1024,7 @@ int __pkvm_guest_share_host(struct pkvm_hyp_vcpu *vcpu, u64 gfn) > pkvm_mkstate(KVM_PGTABLE_PROT_RWX, PKVM_PAGE_SHARED_OWNED), > &vcpu->vcpu.arch.pkvm_memcache, 0)); > WARN_ON(__host_set_page_state_range(phys, PAGE_SIZE, PKVM_PAGE_SHARED_BORROWED)); > + WARN_ON(pkvm_iommu_host_stage2_idmap(phys, phys + PAGE_SIZE, PKVM_HOST_MEM_PROT)); Ha ok I understand your remark yesterday. I thought you'd put pkvm_iommu_host_stage2_idmap() into host_stage2_idmap_locked()... but then it means it tries to map on very host abort. (same though as host_stage2_set_owner_metadata_locked(), I would first update the iommu and then update the page-state) > unlock: > guest_unlock_component(vm); > host_unlock_component(); > -- > 2.55.0.141.g00534a21ce-goog >