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[34.76.60.220]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4953c704bfasm77694915e9.2.2026.07.15.11.43.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Jul 2026 11:43:24 -0700 (PDT) Date: Wed, 15 Jul 2026 18:43:21 +0000 From: Mostafa Saleh To: Vincent Donnefort 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> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Jul 15, 2026 at 06:56:33PM +0100, Vincent Donnefort wrote: > 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(-) [...] > > + > > +/* > > + * 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. I see, I will fix it. > > > + 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) Not sure I understand, the function signature is defined by the walker, or do you mean __snapshot_host_stage2() should call another function were we pass is_memory? That does not seem necessary, the function is small already. > > + 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" ? > Well it's a host stage-2 idmap :), maybe one day we support guests also! > > } > > 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. > I saw that all the callers will WARN on failure, that's why I did not handle the failure. I can move it earlier. > > } > > > > 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. Yes, actually this version is less efficient than v6, as now on VM teardown we re-map all the VM pages including the shared ones which are already in the IOMMU. It's is not terrible but the but the io-pgtable detects that and return -EEXIST which I added new code in this version to ignore. > > (same though as host_stage2_set_owner_metadata_locked(), I would first update > the iommu and then update the page-state) Will do. Thanks, Mostafa >