On Wed, 23 Sept 2026 at 16:17, Lorenzo Stoakes (ARM) <[email protected]> wrote: > > When stage 2 page tables fault the net result may either be that a page is > mapped, an error occurred or the fault should be retried (-EAGAIN). > > When a fault succeeds it may be upgraded to a PMD size via > transparent_hugepage_adjust(). > > In order to support KVM pre-faulting the outcome of the fault and the > mapping size must be recorded. > > Track the mapping size via new kvm_s2_fault_result struct, which is > threaded through gmem_abort(), user_mem_abort() and kvm_s2_fault_map(). > > PKVM and SEA aren't relevant to synthetic pre-faulting so neither > kvm_inject_sea() nor pkvm_mem_abort() are altered. > > Actual hardware faulting doesn't require this information, so > kvm_handle_guest_abort() simply passes NULL kvm_s2_fault_result to > gmem_abort() and user_mem_abort(). > > A non-NULL result also tells the abort handlers that the caller is > pre-faulting rather than a vcpu, in which case -EAGAIN is propagated to the > caller to allow the pre-fault to be retried. > > Likewise, only prepare a KVM_EXIT_MEMORY_FAULT in gmem_abort() when a real > fault is being handled, as this updates vcpu state. > > No functional change intended. > > Suggested-by: Vincent Donnefort <[email protected]> > Reviewed-by: Oliver Upton <[email protected]> > Signed-off-by: Lorenzo Stoakes (ARM) <[email protected]>
Reviewed-by: Fuad Tabba <[email protected]> Cheers, /fuad > --- > arch/arm64/kvm/mmu.c | 43 +++++++++++++++++++++++++++++++------------ > 1 file changed, 31 insertions(+), 12 deletions(-) > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index 9d799f7c1e62..ee2a4f0faa14 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -1659,6 +1659,10 @@ struct kvm_s2_fault_desc { > struct kvm_s2_mmu *mmu; > }; > > +struct kvm_s2_fault_result { > + unsigned long mapping_size; > +}; > + > static bool kvm_s2_fault_is_perm(const struct kvm_s2_fault_desc *s2fd) > { > return esr_fsc_is_permission_fault(s2fd->esr); > @@ -1684,7 +1688,8 @@ static u64 kvm_s2_perm_fault_granule(const struct > kvm_s2_fault_desc *s2fd) > return BIT(ARM64_HW_PGTABLE_LEVEL_SHIFT(level)); > } > > -static int gmem_abort(const struct kvm_s2_fault_desc *s2fd) > +static int gmem_abort(const struct kvm_s2_fault_desc *s2fd, > + struct kvm_s2_fault_result *result) > { > bool write_fault, exec_fault; > bool perm_fault = kvm_s2_fault_is_perm(s2fd); > @@ -1728,8 +1733,10 @@ static int gmem_abort(const struct kvm_s2_fault_desc > *s2fd) > > ret = kvm_gmem_get_pfn(kvm, s2fd->memslot, gfn, &pfn, &page, NULL); > if (ret) { > - kvm_prepare_memory_fault_exit(s2fd->vcpu, s2fd->fault_ipa, > PAGE_SIZE, > - write_fault, exec_fault, false); > + /* If result is non-NULL this is a synthetic fault. */ > + if (!result) > + kvm_prepare_memory_fault_exit(s2fd->vcpu, > s2fd->fault_ipa, PAGE_SIZE, > + write_fault, > exec_fault, false); > kfree(mapping); > return ret; > } > @@ -1784,7 +1791,13 @@ static int gmem_abort(const struct kvm_s2_fault_desc > *s2fd) > if ((prot & KVM_PGTABLE_PROT_W) && !ret) > mark_page_dirty_in_slot(kvm, s2fd->memslot, gfn); > > - return ret != -EAGAIN ? ret : 0; > + if (ret == -EAGAIN) > + return result ? ret : 0; > + > + if (result && !ret) > + result->mapping_size = PAGE_SIZE; > + > + return ret; > } > > struct kvm_s2_fault_vma_info { > @@ -2108,7 +2121,8 @@ static int kvm_s2_fault_compute_prot(const struct > kvm_s2_fault_desc *s2fd, > static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd, > const struct kvm_s2_fault_vma_info *s2vi, > enum kvm_pgtable_prot prot, > - void *memcache) > + void *memcache, > + struct kvm_s2_fault_result *result) > { > enum kvm_pgtable_walk_flags flags = KVM_PGTABLE_WALK_SHARED; > struct kvm_guest_s2_mapping *mapping = NULL; > @@ -2209,12 +2223,17 @@ static int kvm_s2_fault_map(const struct > kvm_s2_fault_desc *s2fd, > mark_page_dirty_in_slot(kvm, s2fd->memslot, > gpa_to_gfn(canonical_ipa)); > > - if (ret != -EAGAIN) > - return ret; > - return 0; > + if (ret == -EAGAIN) > + return result ? ret : 0; > + > + if (result && !ret) > + result->mapping_size = mapping_size; > + > + return ret; > } > > -static int user_mem_abort(const struct kvm_s2_fault_desc *s2fd) > +static int user_mem_abort(const struct kvm_s2_fault_desc *s2fd, > + struct kvm_s2_fault_result *result) > { > bool perm_fault = kvm_s2_fault_is_perm(s2fd); > struct kvm_s2_fault_vma_info s2vi = {}; > @@ -2253,7 +2272,7 @@ static int user_mem_abort(const struct > kvm_s2_fault_desc *s2fd) > return ret; > } > > - return kvm_s2_fault_map(s2fd, &s2vi, prot, memcache); > + return kvm_s2_fault_map(s2fd, &s2vi, prot, memcache, result); > } > > /* Resolve the access fault by making the page young again. */ > @@ -2532,9 +2551,9 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu) > !kvm_s2_fault_is_exec(&s2fd)); > > if (kvm_slot_has_gmem(memslot)) > - ret = gmem_abort(&s2fd); > + ret = gmem_abort(&s2fd, NULL); > else > - ret = user_mem_abort(&s2fd); > + ret = user_mem_abort(&s2fd, NULL); > } > > if (ret == 0) > > -- > 2.55.0 >
