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[34.140.115.198]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43b644bd0dcsm36469256f8f.11.2026.03.24.03.39.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 Mar 2026 03:39:11 -0700 (PDT) Date: Tue, 24 Mar 2026 10:39:07 +0000 From: Vincent Donnefort To: Sebastian Ene Cc: alexandru.elisei@arm.com, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, android-kvm@google.com, catalin.marinas@arm.com, dbrazdil@google.com, joey.gouly@arm.com, kees@kernel.org, mark.rutland@arm.com, maz@kernel.org, oupton@kernel.org, perlarsen@google.com, qperret@google.com, rananta@google.com, smostafa@google.com, suzuki.poulose@arm.com, tabba@google.com, tglx@kernel.org, bgrzesik@google.com, will@kernel.org, yuzenghui@huawei.com Subject: Re: [PATCH 01/14] KVM: arm64: Donate MMIO to the hypervisor Message-ID: References: <20260310124933.830025-1-sebastianene@google.com> <20260310124933.830025-2-sebastianene@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260310124933.830025-2-sebastianene@google.com> On Tue, Mar 10, 2026 at 12:49:20PM +0000, Sebastian Ene wrote: > From: Mostafa Saleh > > Add a function to donate MMIO to the hypervisor so IOMMU hypervisor > drivers can use that to protect the MMIO of IOMMU. > The initial attempt to implement this was to have a new flag to > "___pkvm_host_donate_hyp" to accept MMIO. However that had many problems, > it was quite intrusive for host/hyp to check/set page state to make it > aware of MMIO and to encode the state in the page table in that case. > Which is called in paths that can be sensitive to performance (FFA, VMs..) > > As donating MMIO is very rare, and we don’t need to encode the full > state, it’s reasonable to have a separate function to do this. > It will init the host s2 page table with an invalid leaf with the owner ID > to prevent the host from mapping the page on faults. I am not sure I agree here: * Differentiating between MMIO and Memory is just a fast binary search into the memory regions. * host_donate_hyp isn't a fast path even for memory regions anyway. * Having common functions for changing ownership is more and more helpful (see the SME dvmsync workaround). * There's nothing preventing from having a range here which is safely handled already by host_donate_hyp() > > Also, prevent kvm_pgtable_stage2_unmap() from removing owner ID from > stage-2 PTEs, as this can be triggered from recycle logic under memory > pressure. There is no code relying on this, as all ownership changes is > done via kvm_pgtable_stage2_set_owner() > > For error path in IOMMU drivers, add a function to donate MMIO back > from hyp to host. > > Signed-off-by: Mostafa Saleh > --- > arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 2 + > arch/arm64/kvm/hyp/nvhe/mem_protect.c | 90 +++++++++++++++++++ > arch/arm64/kvm/hyp/pgtable.c | 9 +- > 3 files changed, 94 insertions(+), 7 deletions(-) > > diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > index 5f9d56754e39..8b617e6fc0e0 100644 > --- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > +++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > @@ -31,6 +31,8 @@ enum pkvm_component_id { > }; > > extern unsigned long hyp_nr_cpus; > +int __pkvm_host_donate_hyp_mmio(u64 pfn); > +int __pkvm_hyp_donate_host_mmio(u64 pfn); > > int __pkvm_prot_finalize(void); > int __pkvm_host_share_hyp(u64 pfn); > diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > index 38f66a56a766..0808367c52e5 100644 > --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c > +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > @@ -784,6 +784,96 @@ int __pkvm_host_unshare_hyp(u64 pfn) > return ret; > } > > +int __pkvm_host_donate_hyp_mmio(u64 pfn) > +{ > + u64 phys = hyp_pfn_to_phys(pfn); > + void *virt = __hyp_va(phys); > + int ret; > + kvm_pte_t pte; > + > + if (addr_is_memory(phys)) > + return -EINVAL; > + > + host_lock_component(); > + hyp_lock_component(); > + > + ret = kvm_pgtable_get_leaf(&host_mmu.pgt, phys, &pte, NULL); > + if (ret) > + goto unlock; > + > + if (pte && !kvm_pte_valid(pte)) { > + ret = -EPERM; > + goto unlock; > + } > + > + ret = kvm_pgtable_get_leaf(&pkvm_pgtable, (u64)virt, &pte, NULL); > + if (ret) > + goto unlock; > + if (pte) { > + ret = -EBUSY; > + goto unlock; > + } > + gg> + ret = pkvm_create_mappings_locked(virt, virt + PAGE_SIZE, PAGE_HYP_DEVICE); > gg+ if (ret) > + goto unlock; > + /* > + * We set HYP as the owner of the MMIO pages in the host stage-2, for: > + * - host aborts: host_stage2_adjust_range() would fail for invalid non zero PTEs. > + * - recycle under memory pressure: host_stage2_unmap_dev_all() would call > + * kvm_pgtable_stage2_unmap() which will not clear non zero invalid ptes (counted). > + * - other MMIO donation: Would fail as we check that the PTE is valid or empty. > + */ > + WARN_ON(host_stage2_try(kvm_pgtable_stage2_set_owner, &host_mmu.pgt, phys, > + PAGE_SIZE, &host_s2_pool, PKVM_ID_HYP)); > +unlock: > + hyp_unlock_component(); > + host_unlock_component(); > + > + return ret; > +} > + > +int __pkvm_hyp_donate_host_mmio(u64 pfn) > +{ > + u64 phys = hyp_pfn_to_phys(pfn); > + u64 virt = (u64)__hyp_va(phys); > + size_t size = PAGE_SIZE; > + int ret; > + kvm_pte_t pte; > + > + if (addr_is_memory(phys)) > + return -EINVAL; > + > + host_lock_component(); > + hyp_lock_component(); > + > + ret = kvm_pgtable_get_leaf(&pkvm_pgtable, (u64)virt, &pte, NULL); > + if (ret) > + goto unlock; > + if (!kvm_pte_valid(pte)) { > + ret = -ENOENT; > + goto unlock; > + } > + > + ret = kvm_pgtable_get_leaf(&host_mmu.pgt, phys, &pte, NULL); > + if (ret) > + goto unlock; > + > + if (FIELD_GET(KVM_INVALID_PTE_OWNER_MASK, pte) != PKVM_ID_HYP) { > + ret = -EPERM; > + goto unlock; > + } > + > + WARN_ON(kvm_pgtable_hyp_unmap(&pkvm_pgtable, virt, size) != size); > + WARN_ON(host_stage2_try(kvm_pgtable_stage2_set_owner, &host_mmu.pgt, phys, > + PAGE_SIZE, &host_s2_pool, PKVM_ID_HOST)); > +unlock: > + hyp_unlock_component(); > + host_unlock_component(); > + > + return ret; > +} > + > int __pkvm_host_donate_hyp(u64 pfn, u64 nr_pages) > { > u64 phys = hyp_pfn_to_phys(pfn); > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > index 9b480f947da2..d954058e63ff 100644 > --- a/arch/arm64/kvm/hyp/pgtable.c > +++ b/arch/arm64/kvm/hyp/pgtable.c > @@ -1152,13 +1152,8 @@ static int stage2_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx, > kvm_pte_t *childp = NULL; > bool need_flush = false; > > - if (!kvm_pte_valid(ctx->old)) { > - if (stage2_pte_is_counted(ctx->old)) { > - kvm_clear_pte(ctx->ptep); > - mm_ops->put_page(ctx->ptep); > - } > - return 0; > - } > + if (!kvm_pte_valid(ctx->old)) > + return stage2_pte_is_counted(ctx->old) ? -EPERM : 0; > > if (kvm_pte_table(ctx->old, ctx->level)) { > childp = kvm_pte_follow(ctx->old, mm_ops); > -- > 2.53.0.473.g4a7958ca14-goog >