[PATCH v6 02/25] KVM: arm64: Donate MMIO to the hypervisor

Mostafa Saleh
2026-05-01T11:19:55Z

Add a function to donate MMIO to the hypervisor so IOMMU hypervisor
drivers can protect and access the MMIO of IOMMUs.

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.

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 the error path in IOMMU drivers, add a function to donate MMIO
back from hyp to host. However, that leaks the hypervisor virtual
address range which should be acceptable as this is quite rare and
it matches the behaviour of fix_map/block.

Signed-off-by: Mostafa Saleh <smostafa@google.com>
---
arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 2 +
arch/arm64/kvm/hyp/nvhe/mem_protect.c | 119 +++++++++++++++++-
arch/arm64/kvm/hyp/pgtable.c | 9 +-
3 files changed, 121 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
index 3cbfae0e3dda..ff440204d2c7 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
@@ -36,6 +36,8 @@ int __pkvm_guest_share_host(struct pkvm_hyp_vcpu *vcpu, u64 gfn);
int __pkvm_guest_unshare_host(struct pkvm_hyp_vcpu *vcpu, u64 gfn);
int __pkvm_host_unshare_hyp(u64 pfn);
int __pkvm_host_donate_hyp(u64 pfn, u64 nr_pages);
+int __pkvm_host_donate_hyp_mmio(phys_addr_t addr, size_t size, unsigned long *haddr);
+int __pkvm_hyp_donate_host_mmio(phys_addr_t addr, size_t size);
int __pkvm_hyp_donate_host(u64 pfn, u64 nr_pages);
int __pkvm_host_share_ffa(u64 pfn, u64 nr_pages);
int __pkvm_host_unshare_ffa(u64 pfn, u64 nr_pages);
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 28a471d1927c..2fb20a63a417 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -353,6 +353,38 @@ int __pkvm_prot_finalize(void)
return 0;
}

+/* Unmap MMIO region while skipping donated PTEs. */
+static int host_stage2_unmap_mmio_region(u64 start, u64 size)
+{
+ struct kvm_pgtable *pgt = &host_mmu.pgt;
+ u64 unmap_start = start;
+ u64 addr = start;
+ kvm_pte_t pte;
+ int ret = 0;
+ u8 level;
+
+ while (addr < start + size) {
+ ret = kvm_pgtable_get_leaf(pgt, addr, &pte, &level);
+ if (ret)
+ return ret;
+ if (!kvm_pte_valid(pte) && pte != 0) {
+ if (addr > unmap_start) {
+ ret = kvm_pgtable_stage2_unmap(pgt, unmap_start,
+ addr - unmap_start);
+ if (ret)
+ return ret;
+ }
+ addr += kvm_granule_size(level);
+ unmap_start = addr;
+ } else {
+ addr += kvm_granule_size(level);
+ }
+ }
+ if (addr > unmap_start)
+ ret = kvm_pgtable_stage2_unmap(pgt, unmap_start, addr - unmap_start);
+ return ret;
+}
+
static int host_stage2_unmap_dev_all(void)
{
struct kvm_pgtable *pgt = &host_mmu.pgt;
@@ -363,11 +395,11 @@ static int host_stage2_unmap_dev_all(void)
/* Unmap all non-memory regions to recycle the pages */
for (i = 0; i < hyp_memblock_nr; i++, addr = reg->base + reg->size) {
reg = &hyp_memory[i];
- ret = kvm_pgtable_stage2_unmap(pgt, addr, reg->base - addr);
+ ret = host_stage2_unmap_mmio_region(addr, reg->base - addr);
if (ret)
return ret;
}
- return kvm_pgtable_stage2_unmap(pgt, addr, BIT(pgt->ia_bits) - addr);
+ return host_stage2_unmap_mmio_region(addr, BIT(pgt->ia_bits) - addr);
}

/*
@@ -1087,6 +1119,89 @@ int __pkvm_host_donate_hyp(u64 pfn, u64 nr_pages)
return ret;
}

+int __pkvm_host_donate_hyp_mmio(phys_addr_t addr, size_t size, unsigned long *haddr)
+{
+ kvm_pte_t pte;
+ u64 offset;
+ int ret;
+
+ /* Only before de-privilege. */
+ if (static_branch_unlikely(&kvm_protected_mode_initialized))
+ return -EPERM;
+
+ if (!PAGE_ALIGNED(addr | size))
+ return -EINVAL;
+
+ ret = __pkvm_create_private_mapping(addr, size, PAGE_HYP_DEVICE, haddr);
+ if (ret)
+ return ret;
+
+ host_lock_component();
+ for (offset = 0; offset < size; offset += PAGE_SIZE) {
+ if (addr_is_memory(addr + offset)) {
+ ret = -EINVAL;
+ goto unlock;
+ }
+ ret = kvm_pgtable_get_leaf(&host_mmu.pgt, addr + offset, &pte, NULL);
+ if (ret)
+ goto unlock;
+ if (pte && !kvm_pte_valid(pte)) {
+ ret = -EPERM;
+ 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.
+ */
+ ret = host_stage2_try(kvm_pgtable_stage2_annotate, &host_mmu.pgt,
+ addr, size, &host_s2_pool,
+ KVM_HOST_INVALID_PTE_TYPE_DONATION,
+ FIELD_PREP(KVM_HOST_DONATION_PTE_OWNER_MASK, PKVM_ID_HYP));
+unlock:
+ host_unlock_component();
+ return ret;
+}
+
+int __pkvm_hyp_donate_host_mmio(phys_addr_t addr, size_t size)
+{
+ kvm_pte_t pte;
+ u64 offset;
+ int ret = 0;
+
+ if (static_branch_unlikely(&kvm_protected_mode_initialized))
+ return -EPERM;
+
+ if (!PAGE_ALIGNED(addr | size))
+ return -EINVAL;
+
+ host_lock_component();
+ for (offset = 0; offset < size; offset += PAGE_SIZE) {
+ if (addr_is_memory(addr + offset)) {
+ ret = -EINVAL;
+ goto unlock;
+ }
+ ret = kvm_pgtable_get_leaf(&host_mmu.pgt, addr + offset, &pte, NULL);
+ if (ret)
+ goto unlock;
+ if (!pte || kvm_pte_valid(pte)) {
+ ret = -EINVAL;
+ goto unlock;
+ }
+ if (FIELD_GET(KVM_HOST_DONATION_PTE_OWNER_MASK, pte) != PKVM_ID_HYP) {
+ ret = -EPERM;
+ goto unlock;
+ }
+ }
+ WARN_ON(host_stage2_idmap_locked(addr, size, PKVM_HOST_MMIO_PROT));
+unlock:
+ host_unlock_component();
+ return ret;
+}
+
int __pkvm_hyp_donate_host(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 0c1defa5fb0f..b64a50f9bfa8 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -1159,13 +1159,8 @@ 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);
--
2.54.0.545.g6539524ca2-goog