[PATCH 02/17] KVM: arm64: Make fault_ipa immutable

[Fuad Tabba]

On Mon, 16 Mar 2026 at 17:55, Marc Zyngier <maz at kernel.org> wrote:
>
> Updating fault_ipa is conceptually annoying, as it changes something
> that is a property of the fault itself.
>
> Stop doing so and instead use fault->gfn as the sole piece of state
> that can be used to represent the faulting IPA.
>
> At the same time, introduce get_canonical_gfn() for the couple of case
> we're we are concerned with the memslot-related IPA and not the faulting
> one.
>
> Signed-off-by: Marc Zyngier <maz at kernel.org>

Reviewed-by: Fuad Tabba <tabba at google.com>

Cheers,
/fuad

> ---
>  arch/arm64/kvm/mmu.c | 38 ++++++++++++++++++++++++++------------
>  1 file changed, 26 insertions(+), 12 deletions(-)
>
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index fe8f8057cf412..ab8a269d4366d 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1400,10 +1400,10 @@ static bool fault_supports_stage2_huge_mapping(struct kvm_memory_slot *memslot,
>   */
>  static long
>  transparent_hugepage_adjust(struct kvm *kvm, struct kvm_memory_slot *memslot,
> -                           unsigned long hva, kvm_pfn_t *pfnp,
> -                           phys_addr_t *ipap)
> +                           unsigned long hva, kvm_pfn_t *pfnp, gfn_t *gfnp)
>  {
>         kvm_pfn_t pfn = *pfnp;
> +       gfn_t gfn = *gfnp;
>
>         /*
>          * Make sure the adjustment is done only for THP pages. Also make
> @@ -1419,7 +1419,8 @@ transparent_hugepage_adjust(struct kvm *kvm, struct kvm_memory_slot *memslot,
>                 if (sz < PMD_SIZE)
>                         return PAGE_SIZE;
>
> -               *ipap &= PMD_MASK;
> +               gfn &= ~(PTRS_PER_PMD - 1);
> +               *gfnp = gfn;
>                 pfn &= ~(PTRS_PER_PMD - 1);
>                 *pfnp = pfn;
>
> @@ -1735,7 +1736,6 @@ static int kvm_s2_fault_get_vma_info(struct kvm_s2_fault *fault)
>  {
>         struct vm_area_struct *vma;
>         struct kvm *kvm = fault->vcpu->kvm;
> -       phys_addr_t ipa;
>
>         mmap_read_lock(current->mm);
>         vma = vma_lookup(current->mm, fault->hva);
> @@ -1753,9 +1753,7 @@ static int kvm_s2_fault_get_vma_info(struct kvm_s2_fault *fault)
>          * mapping size to ensure we find the right PFN and lay down the
>          * mapping in the right place.
>          */
> -       fault->fault_ipa = ALIGN_DOWN(fault->fault_ipa, fault->vma_pagesize);
> -       ipa = fault->nested ? kvm_s2_trans_output(fault->nested) : fault->fault_ipa;
> -       fault->gfn = ALIGN_DOWN(ipa, fault->vma_pagesize) >> PAGE_SHIFT;
> +       fault->gfn = ALIGN_DOWN(fault->fault_ipa, fault->vma_pagesize) >> PAGE_SHIFT;
>
>         fault->mte_allowed = kvm_vma_mte_allowed(vma);
>
> @@ -1777,6 +1775,17 @@ static int kvm_s2_fault_get_vma_info(struct kvm_s2_fault *fault)
>         return 0;
>  }
>
> +static gfn_t get_canonical_gfn(struct kvm_s2_fault *fault)
> +{
> +       phys_addr_t ipa;
> +
> +       if (!fault->nested)
> +               return fault->gfn;
> +
> +       ipa = kvm_s2_trans_output(fault->nested);
> +       return ALIGN_DOWN(ipa, fault->vma_pagesize) >> PAGE_SHIFT;
> +}
> +
>  static int kvm_s2_fault_pin_pfn(struct kvm_s2_fault *fault)
>  {
>         int ret;
> @@ -1785,7 +1794,7 @@ static int kvm_s2_fault_pin_pfn(struct kvm_s2_fault *fault)
>         if (ret)
>                 return ret;
>
> -       fault->pfn = __kvm_faultin_pfn(fault->memslot, fault->gfn,
> +       fault->pfn = __kvm_faultin_pfn(fault->memslot, get_canonical_gfn(fault),
>                                        fault->write_fault ? FOLL_WRITE : 0,
>                                        &fault->writable, &fault->page);
>         if (unlikely(is_error_noslot_pfn(fault->pfn))) {
> @@ -1885,6 +1894,11 @@ static int kvm_s2_fault_compute_prot(struct kvm_s2_fault *fault)
>         return 0;
>  }
>
> +static phys_addr_t get_ipa(const struct kvm_s2_fault *fault)
> +{
> +       return gfn_to_gpa(fault->gfn);
> +}
> +
>  static int kvm_s2_fault_map(struct kvm_s2_fault *fault, void *memcache)
>  {
>         struct kvm *kvm = fault->vcpu->kvm;
> @@ -1909,7 +1923,7 @@ static int kvm_s2_fault_map(struct kvm_s2_fault *fault, void *memcache)
>                 } else {
>                         fault->vma_pagesize = transparent_hugepage_adjust(kvm, fault->memslot,
>                                                                           fault->hva, &fault->pfn,
> -                                                                         &fault->fault_ipa);
> +                                                                         &fault->gfn);
>
>                         if (fault->vma_pagesize < 0) {
>                                 ret = fault->vma_pagesize;
> @@ -1932,10 +1946,10 @@ static int kvm_s2_fault_map(struct kvm_s2_fault *fault, void *memcache)
>                  * PTE, which will be preserved.
>                  */
>                 fault->prot &= ~KVM_NV_GUEST_MAP_SZ;
> -               ret = KVM_PGT_FN(kvm_pgtable_stage2_relax_perms)(pgt, fault->fault_ipa,
> +               ret = KVM_PGT_FN(kvm_pgtable_stage2_relax_perms)(pgt, get_ipa(fault),
>                                                                  fault->prot, flags);
>         } else {
> -               ret = KVM_PGT_FN(kvm_pgtable_stage2_map)(pgt, fault->fault_ipa, fault->vma_pagesize,
> +               ret = KVM_PGT_FN(kvm_pgtable_stage2_map)(pgt, get_ipa(fault), fault->vma_pagesize,
>                                                          __pfn_to_phys(fault->pfn), fault->prot,
>                                                          memcache, flags);
>         }
> @@ -1946,7 +1960,7 @@ static int kvm_s2_fault_map(struct kvm_s2_fault *fault, void *memcache)
>
>         /* Mark the fault->page dirty only if the fault is handled successfully */
>         if (fault->writable && !ret)
> -               mark_page_dirty_in_slot(kvm, fault->memslot, fault->gfn);
> +               mark_page_dirty_in_slot(kvm, fault->memslot, get_canonical_gfn(fault));
>
>         if (ret != -EAGAIN)
>                 return ret;
> --
> 2.47.3
>