[PATCH v5 02/15] KVM: arm64: Add KVM_PGTABLE_PROT_DIRTY
Oliver Upton
oupton at kernel.org
Tue Sep 29 17:35:15 PDT 2026
On Tue, Sep 29, 2026 at 06:36:42PM +0800, Tian Zheng wrote:
> @@ -731,8 +731,12 @@ static int stage2_set_prot_attr(struct kvm_pgtable *pgt, enum kvm_pgtable_prot p
> if (prot & KVM_PGTABLE_PROT_R)
> attr |= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R;
>
> - if (prot & KVM_PGTABLE_PROT_W)
> - attr |= KVM_PTE_LEAF_ATTR_HI_S2_DBM | KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W;
> + if (prot & KVM_PGTABLE_PROT_W) {
> + attr |= KVM_PTE_LEAF_ATTR_HI_S2_DBM;
> +
> + if (prot & KVM_PGTABLE_PROT_DIRTY)
> + attr |= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W;
> + }
Can you introduce the dirty state first? You're temporarily setting
DBM+S2AP[1] as a workaround in the preceding patch.
Then we can have it encoded such that when FEAT_HAFDBS is implemented:
KVM_PGTABLE_PROT_W => KVM_PTE_LEAF_ATTR_HI_S2_DBM
KVM_PGTABLE_PROT_DIRTY => KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W
And if FEAT_HAFDBS is *not* implemented:
KVM_PGTABLE_PROT_W => KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W
KVM_PGTABLE_PROT_DIRTY => KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W
i.e. aliasing both to bit 7.
Thanks,
Oliver
> if (!kvm_lpa2_is_enabled())
> attr |= FIELD_PREP(KVM_PTE_LEAF_ATTR_LO_S2_SH, sh);
> @@ -753,9 +757,13 @@ enum kvm_pgtable_prot kvm_pgtable_stage2_pte_prot(kvm_pte_t pte)
>
> if (pte & KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R)
> prot |= KVM_PGTABLE_PROT_R;
> - if (pte & KVM_PTE_LEAF_ATTR_HI_S2_DBM)
> + if (pte & KVM_PTE_LEAF_ATTR_HI_S2_DBM) {
> prot |= KVM_PGTABLE_PROT_W;
>
> + if (pte & KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W)
> + prot |= KVM_PGTABLE_PROT_DIRTY;
> + }
> +
> switch (FIELD_GET(KVM_PTE_LEAF_ATTR_HI_S2_XN, pte)) {
> case 0b00:
> prot |= KVM_PGTABLE_PROT_PX | KVM_PGTABLE_PROT_UX;
> @@ -1288,7 +1296,6 @@ static int stage2_update_leaf_attrs(struct kvm_pgtable *pgt, u64 addr,
> int kvm_pgtable_stage2_wrprotect(struct kvm_pgtable *pgt, u64 addr, u64 size)
> {
> return stage2_update_leaf_attrs(pgt, addr, size, 0,
> - KVM_PTE_LEAF_ATTR_HI_S2_DBM |
> KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W,
> NULL, NULL,
> KVM_PGTABLE_WALK_IGNORE_EAGAIN);
> @@ -1368,8 +1375,12 @@ int kvm_pgtable_stage2_relax_perms(struct kvm_pgtable *pgt, u64 addr,
> if (prot & KVM_PGTABLE_PROT_R)
> set |= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R;
>
> - if (prot & KVM_PGTABLE_PROT_W)
> - set |= KVM_PTE_LEAF_ATTR_HI_S2_DBM | KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W;
> + if (prot & KVM_PGTABLE_PROT_W) {
> + set |= KVM_PTE_LEAF_ATTR_HI_S2_DBM;
> +
> + if (prot & KVM_PGTABLE_PROT_DIRTY)
> + set |= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W;
> + }
>
> if (prot & KVM_PGTABLE_PROT_X) {
> ret = stage2_set_xn_attr(prot, &xn);
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 2d44cd6a5aed..698a87e85a6d 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1221,7 +1221,9 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
> struct kvm_pgtable *pgt = mmu->pgt;
> enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_DEVICE |
> KVM_PGTABLE_PROT_R |
> - (writable ? KVM_PGTABLE_PROT_W : 0);
> + (writable ?
> + (KVM_PGTABLE_PROT_W | KVM_PGTABLE_PROT_DIRTY) :
> + 0);
>
> if (is_protected_kvm_enabled())
> return -EPERM;
> @@ -1587,7 +1589,7 @@ static enum kvm_pgtable_prot adjust_nested_fault_perms(struct kvm_s2_trans *nest
> enum kvm_pgtable_prot prot)
> {
> if (!kvm_s2_trans_writable(nested))
> - prot &= ~KVM_PGTABLE_PROT_W;
> + prot &= ~(KVM_PGTABLE_PROT_W | KVM_PGTABLE_PROT_DIRTY);
> if (!kvm_s2_trans_readable(nested))
> prot &= ~KVM_PGTABLE_PROT_R;
>
> @@ -1658,7 +1660,7 @@ static int gmem_abort(const struct kvm_s2_fault_desc *s2fd)
> }
>
> if (!(s2fd->memslot->flags & KVM_MEM_READONLY))
> - prot |= KVM_PGTABLE_PROT_W;
> + prot |= KVM_PGTABLE_PROT_W | KVM_PGTABLE_PROT_DIRTY;
>
> if (s2fd->nested)
> prot = adjust_nested_fault_perms(s2fd->nested, prot);
> @@ -1690,10 +1692,17 @@ static int gmem_abort(const struct kvm_s2_fault_desc *s2fd)
> }
>
> out_unlock:
> + /*
> + * Dirty the folio for any write-permitting mapping: hardware can
> + * promote a writable-clean entry to writable-dirty without a VM
> + * exit, so a clean release could lose a guest write at reclaim.
> + * The dirty bitmap is only marked for mappings installed dirty,
> + * or pre-copy would treat every writable page as dirty.
> + */
> kvm_release_faultin_page(kvm, page, !!ret, prot & KVM_PGTABLE_PROT_W);
> kvm_fault_unlock(kvm);
>
> - if ((prot & KVM_PGTABLE_PROT_W) && !ret)
> + if ((prot & KVM_PGTABLE_PROT_DIRTY) && !ret)
> mark_page_dirty_in_slot(kvm, s2fd->memslot, gfn);
>
> return ret != -EAGAIN ? ret : 0;
> @@ -1993,11 +2002,14 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
>
> *prot = KVM_PGTABLE_PROT_R;
>
> - if (s2vi->map_writable && (s2vi->device ||
> - !memslot_is_logging(s2fd->memslot) ||
> - kvm_is_write_fault(s2fd->vcpu)))
> + if (s2vi->map_writable) {
> *prot |= KVM_PGTABLE_PROT_W;
>
> + if (s2vi->device || !memslot_is_logging(s2fd->memslot) ||
> + kvm_is_write_fault(s2fd->vcpu))
> + *prot |= KVM_PGTABLE_PROT_DIRTY;
> + }
> +
> if (s2fd->nested)
> *prot = adjust_nested_fault_perms(s2fd->nested, *prot);
>
> @@ -2028,7 +2040,7 @@ static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd,
> void *memcache)
> {
> enum kvm_pgtable_walk_flags flags = KVM_PGTABLE_WALK_SHARED;
> - bool writable = prot & KVM_PGTABLE_PROT_W;
> + bool dirty = prot & KVM_PGTABLE_PROT_DIRTY;
> struct kvm *kvm = s2fd->vcpu->kvm;
> struct kvm_pgtable *pgt;
> long perm_fault_granule;
> @@ -2091,7 +2103,11 @@ static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd,
> }
>
> out_unlock:
> - kvm_release_faultin_page(kvm, s2vi->page, !!ret, writable);
> + /*
> + * Speculative folio dirtying: W, not DIRTY, per the contract
> + * documented in kvm_release_faultin_page().
> + */
> + kvm_release_faultin_page(kvm, s2vi->page, !!ret, prot & KVM_PGTABLE_PROT_W);
> kvm_fault_unlock(kvm);
>
> /*
> @@ -2099,7 +2115,7 @@ static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd,
> * making sure we adjust the canonical IPA if the mapping size has
> * been updated (via a THP upgrade, for example).
> */
> - if (writable && !ret) {
> + if (dirty && !ret) {
> phys_addr_t ipa = gfn_to_gpa(get_canonical_gfn(s2fd, s2vi));
> ipa &= ~(mapping_size - 1);
> mark_page_dirty_in_slot(kvm, s2fd->memslot, gpa_to_gfn(ipa));
> diff --git a/arch/arm64/kvm/ptdump.c b/arch/arm64/kvm/ptdump.c
> index b0cb8d84a9e9..a1251e252b4f 100644
> --- a/arch/arm64/kvm/ptdump.c
> +++ b/arch/arm64/kvm/ptdump.c
> @@ -45,6 +45,12 @@ static const struct ptdump_prot_bits stage2_pte_bits[] = {
> .set = "W",
> .clear = " ",
> },
> + {
> + .mask = KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W,
> + .val = KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W,
> + .set = "D",
> + .clear = "C",
> + },
> {
> .mask = KVM_PTE_LEAF_ATTR_HI_S2_XN,
> .val = 0b00UL << __bf_shf(KVM_PTE_LEAF_ATTR_HI_S2_XN),
> --
> 2.43.0
>
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