[PATCH v5 02/15] KVM: arm64: Add KVM_PGTABLE_PROT_DIRTY
Tian Zheng
zhengtian10 at huawei.com
Tue Sep 29 19:57:33 PDT 2026
On 9/30/2026 8:35 AM, Oliver Upton wrote:
> 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
>
Hi Oliver,
You're right, the intermediate DBM+S2AP[1] encoding is not worth
keeping. I'll introduce KVM_PGTABLE_PROT_DIRTY first, aliased to
S2AP[1] alongside PROT_W, with no behavior change. In the next
version I'll then switch the encoding so that:
- with FEAT_HAFDBS: PROT_W -> DBM, PROT_DIRTY -> S2AP[1]
- without FEAT_HAFDBS: both -> S2AP[1]
as you described.
Thanks,
Tian
>> 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
>>
More information about the linux-arm-kernel
mailing list