[PATCH 14/17] KVM: arm64: Move device mapping management into kvm_s2_fault_pin_pfn()
Fuad Tabba
tabba at google.com
Tue Mar 17 08:41:06 PDT 2026
On Mon, 16 Mar 2026 at 17:55, Marc Zyngier <maz at kernel.org> wrote:
>
> Attributes computed for devices are computed very late in the fault
> handling process, meanning they are mutable for that long.
>
> Introduce both 'device' and 'map_non_cacheable' attributes to the
> vma_info structure, allowing that information to be set in stone
> earlier, in kvm_s2_fault_pin_pfn().
>
> Signed-off-by: Marc Zyngier <maz at kernel.org>
Reviewed-by: Fuad Tabba <tabba at google.com>
Cheers,
/fuad
> ---
> arch/arm64/kvm/mmu.c | 52 ++++++++++++++++++++++++--------------------
> 1 file changed, 29 insertions(+), 23 deletions(-)
>
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index ac4bfcc33aeb1..97cb3585eba03 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1656,9 +1656,11 @@ struct kvm_s2_fault_vma_info {
> struct page *page;
> kvm_pfn_t pfn;
> gfn_t gfn;
> + bool device;
> bool mte_allowed;
> bool is_vma_cacheable;
> bool map_writable;
> + bool map_non_cacheable;
> };
>
> static short kvm_s2_resolve_vma_size(const struct kvm_s2_fault_desc *s2fd,
> @@ -1728,7 +1730,6 @@ static short kvm_s2_resolve_vma_size(const struct kvm_s2_fault_desc *s2fd,
> }
>
> struct kvm_s2_fault {
> - bool s2_force_noncacheable;
> enum kvm_pgtable_prot prot;
> };
>
> @@ -1738,7 +1739,6 @@ static bool kvm_s2_fault_is_perm(const struct kvm_s2_fault_desc *s2fd)
> }
>
> static int kvm_s2_fault_get_vma_info(const struct kvm_s2_fault_desc *s2fd,
> - struct kvm_s2_fault *fault,
> struct kvm_s2_fault_vma_info *s2vi)
> {
> struct vm_area_struct *vma;
> @@ -1794,12 +1794,11 @@ static gfn_t get_canonical_gfn(const struct kvm_s2_fault_desc *s2fd,
> }
>
> static int kvm_s2_fault_pin_pfn(const struct kvm_s2_fault_desc *s2fd,
> - struct kvm_s2_fault *fault,
> struct kvm_s2_fault_vma_info *s2vi)
> {
> int ret;
>
> - ret = kvm_s2_fault_get_vma_info(s2fd, fault, s2vi);
> + ret = kvm_s2_fault_get_vma_info(s2fd, s2vi);
> if (ret)
> return ret;
>
> @@ -1814,16 +1813,6 @@ static int kvm_s2_fault_pin_pfn(const struct kvm_s2_fault_desc *s2fd,
> return -EFAULT;
> }
>
> - return 1;
> -}
> -
> -static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
> - struct kvm_s2_fault *fault,
> - const struct kvm_s2_fault_vma_info *s2vi)
> -{
> - struct kvm *kvm = s2fd->vcpu->kvm;
> - bool writable = s2vi->map_writable;
> -
> /*
> * Check if this is non-struct page memory PFN, and cannot support
> * CMOs. It could potentially be unsafe to access as cacheable.
> @@ -1842,8 +1831,10 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
> * S2FWB and CACHE DIC are mandatory to avoid the need for
> * cache maintenance.
> */
> - if (!kvm_supports_cacheable_pfnmap())
> + if (!kvm_supports_cacheable_pfnmap()) {
> + kvm_release_faultin_page(s2fd->vcpu->kvm, s2vi->page, true, false);
> return -EFAULT;
> + }
> } else {
> /*
> * If the page was identified as device early by looking at
> @@ -1855,9 +1846,24 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
> * In both cases, we don't let transparent_hugepage_adjust()
> * change things at the last minute.
> */
> - fault->s2_force_noncacheable = true;
> + s2vi->map_non_cacheable = true;
> }
> - } else if (memslot_is_logging(s2fd->memslot) && !kvm_is_write_fault(s2fd->vcpu)) {
> +
> + s2vi->device = true;
> + }
> +
> + return 1;
> +}
> +
> +static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
> + struct kvm_s2_fault *fault,
> + const struct kvm_s2_fault_vma_info *s2vi)
> +{
> + struct kvm *kvm = s2fd->vcpu->kvm;
> + bool writable = s2vi->map_writable;
> +
> + if (!s2vi->device && memslot_is_logging(s2fd->memslot) &&
> + !kvm_is_write_fault(s2fd->vcpu)) {
> /*
> * Only actually map the page as writable if this was a write
> * fault.
> @@ -1865,7 +1871,7 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
> writable = false;
> }
>
> - if (kvm_vcpu_trap_is_exec_fault(s2fd->vcpu) && fault->s2_force_noncacheable)
> + if (kvm_vcpu_trap_is_exec_fault(s2fd->vcpu) && s2vi->map_non_cacheable)
> return -ENOEXEC;
>
> /*
> @@ -1888,7 +1894,7 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
> if (kvm_vcpu_trap_is_exec_fault(s2fd->vcpu))
> fault->prot |= KVM_PGTABLE_PROT_X;
>
> - if (fault->s2_force_noncacheable)
> + if (s2vi->map_non_cacheable)
> fault->prot |= (s2vi->vm_flags & VM_ALLOW_ANY_UNCACHED) ?
> KVM_PGTABLE_PROT_NORMAL_NC : KVM_PGTABLE_PROT_DEVICE;
> else if (cpus_have_final_cap(ARM64_HAS_CACHE_DIC))
> @@ -1897,7 +1903,7 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
> if (s2fd->nested)
> adjust_nested_exec_perms(kvm, s2fd->nested, &fault->prot);
>
> - if (!kvm_s2_fault_is_perm(s2fd) && !fault->s2_force_noncacheable && kvm_has_mte(kvm)) {
> + if (!kvm_s2_fault_is_perm(s2fd) && !s2vi->map_non_cacheable && kvm_has_mte(kvm)) {
> /* Check the VMM hasn't introduced a new disallowed VMA */
> if (!s2vi->mte_allowed)
> return -EFAULT;
> @@ -1937,7 +1943,7 @@ static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd,
> * backed by a THP and thus use block mapping if possible.
> */
> if (mapping_size == PAGE_SIZE &&
> - !(s2vi->max_map_size == PAGE_SIZE || fault->s2_force_noncacheable)) {
> + !(s2vi->max_map_size == PAGE_SIZE || s2vi->map_non_cacheable)) {
> if (perm_fault_granule > PAGE_SIZE) {
> mapping_size = perm_fault_granule;
> } else {
> @@ -1951,7 +1957,7 @@ static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd,
> }
> }
>
> - if (!perm_fault_granule && !fault->s2_force_noncacheable && kvm_has_mte(kvm))
> + if (!perm_fault_granule && !s2vi->map_non_cacheable && kvm_has_mte(kvm))
> sanitise_mte_tags(kvm, pfn, mapping_size);
>
> /*
> @@ -2016,7 +2022,7 @@ static int user_mem_abort(const struct kvm_s2_fault_desc *s2fd)
> * Let's check if we will get back a huge fault->page backed by hugetlbfs, or
> * get block mapping for device MMIO region.
> */
> - ret = kvm_s2_fault_pin_pfn(s2fd, &fault, &s2vi);
> + ret = kvm_s2_fault_pin_pfn(s2fd, &s2vi);
> if (ret != 1)
> return ret;
>
> --
> 2.47.3
>
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