[PATCH v1 03/13] KVM: s390: use __kvm_faultin_pfn()

Claudio Imbrenda
2025-01-08T18:14:57Z

Refactor the existing page fault handling code to use __kvm_faultin_pfn().

This possible now that memslots are always present.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
arch/s390/kvm/kvm-s390.c | 92 +++++++++++++++++++++++++++++++---------
arch/s390/mm/gmap.c | 1 +
2 files changed, 73 insertions(+), 20 deletions(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 797b8503c162..8e4e7e45238b 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -4794,11 +4794,66 @@ static void kvm_s390_assert_primary_as(struct kvm_vcpu *vcpu)
current->thread.gmap_int_code, current->thread.gmap_teid.val);
}

+static int kvm_s390_handle_dat_fault(struct kvm_vcpu *vcpu, gfn_t gfn, gpa_t gaddr,
+ unsigned int flags)
+{
+ struct kvm_memory_slot *slot;
+ unsigned int fault_flags;
+ bool writable, unlocked;
+ unsigned long vmaddr;
+ struct page *page;
+ kvm_pfn_t pfn;
+ int rc;
+
+ slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
+ if (!slot || slot->flags & KVM_MEMSLOT_INVALID)
+ return vcpu_post_run_addressing_exception(vcpu);
+
+ fault_flags = flags & FOLL_WRITE ? FAULT_FLAG_WRITE : 0;
+ if (vcpu->arch.gmap->pfault_enabled)
+ flags |= FOLL_NOWAIT;
+ vmaddr = __gfn_to_hva_memslot(slot, gfn);
+
+try_again:
+ pfn = __kvm_faultin_pfn(slot, gfn, flags, &writable, &page);
+
+ /* Access outside memory, inject addressing exception */
+ if (is_noslot_pfn(pfn))
+ return vcpu_post_run_addressing_exception(vcpu);
+ /* Signal pending: try again */
+ if (pfn == KVM_PFN_ERR_SIGPENDING)
+ return -EAGAIN;
+
+ /* Needs I/O, try to setup async pfault (only possible with FOLL_NOWAIT) */
+ if (pfn == KVM_PFN_ERR_NEEDS_IO) {
+ trace_kvm_s390_major_guest_pfault(vcpu);
+ if (kvm_arch_setup_async_pf(vcpu))
+ return 0;
+ vcpu->stat.pfault_sync++;
+ /* Could not setup async pfault, try again synchronously */
+ flags &= ~FOLL_NOWAIT;
+ goto try_again;
+ }
+ /* Any other error */
+ if (is_error_pfn(pfn))
+ return -EFAULT;
+
+ /* Success */
+ mmap_read_lock(vcpu->arch.gmap->mm);
+ /* Mark the userspace PTEs as young and/or dirty, to avoid page fault loops */
+ rc = fixup_user_fault(vcpu->arch.gmap->mm, vmaddr, fault_flags, &unlocked);
+ if (!rc)
+ rc = __gmap_link(vcpu->arch.gmap, gaddr, vmaddr);
+ kvm_release_faultin_page(vcpu->kvm, page, false, writable);
+ mmap_read_unlock(vcpu->arch.gmap->mm);
+ return rc;
+}
+
static int vcpu_post_run_handle_fault(struct kvm_vcpu *vcpu)
{
+ unsigned long gaddr, gaddr_tmp;
unsigned int flags = 0;
- unsigned long gaddr;
- int rc = 0;
+ gfn_t gfn;

gaddr = current->thread.gmap_teid.addr * PAGE_SIZE;
if (kvm_s390_cur_gmap_fault_is_write())
@@ -4850,29 +4905,26 @@ static int vcpu_post_run_handle_fault(struct kvm_vcpu *vcpu)
case PGM_REGION_SECOND_TRANS:
case PGM_REGION_THIRD_TRANS:
kvm_s390_assert_primary_as(vcpu);
- if (vcpu->arch.gmap->pfault_enabled) {
- rc = gmap_fault(vcpu->arch.gmap, gaddr, flags | FAULT_FLAG_RETRY_NOWAIT);
- if (rc == -EFAULT)
- return vcpu_post_run_addressing_exception(vcpu);
- if (rc == -EAGAIN) {
- trace_kvm_s390_major_guest_pfault(vcpu);
- if (kvm_arch_setup_async_pf(vcpu))
- return 0;
- vcpu->stat.pfault_sync++;
- } else {
- return rc;
- }
- }
- rc = gmap_fault(vcpu->arch.gmap, gaddr, flags);
- if (rc == -EFAULT) {
- if (kvm_is_ucontrol(vcpu->kvm)) {
+
+ gfn = gpa_to_gfn(gaddr);
+ if (kvm_is_ucontrol(vcpu->kvm)) {
+ /*
+ * This translates the per-vCPU guest address into a
+ * fake guest address, which can then be used with the
+ * fake memslots that are identity mapping userspace.
+ * This allows ucontrol VMs to use the normal fault
+ * resolution path, like normal VMs.
+ */
+ gaddr_tmp = gmap_translate(vcpu->arch.gmap, gaddr);
+ if (gaddr_tmp == -EFAULT) {
vcpu->run->exit_reason = KVM_EXIT_S390_UCONTROL;
vcpu->run->s390_ucontrol.trans_exc_code = gaddr;
vcpu->run->s390_ucontrol.pgm_code = 0x10;
return -EREMOTE;
}
- return vcpu_post_run_addressing_exception(vcpu);
+ gfn = gpa_to_gfn(gaddr_tmp);
}
+ return kvm_s390_handle_dat_fault(vcpu, gfn, gaddr, flags);
break;
default:
KVM_BUG(1, vcpu->kvm, "Unexpected program interrupt 0x%x, TEID 0x%016lx",
@@ -4880,7 +4932,7 @@ static int vcpu_post_run_handle_fault(struct kvm_vcpu *vcpu)
send_sig(SIGSEGV, current, 0);
break;
}
- return rc;
+ return 0;
}

static int vcpu_post_run(struct kvm_vcpu *vcpu, int exit_reason)
diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index 16b8a36c56de..3aacef77c174 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -605,6 +605,7 @@ int __gmap_link(struct gmap *gmap, unsigned long gaddr, unsigned long vmaddr)
radix_tree_preload_end();
return rc;
}
+EXPORT_SYMBOL(__gmap_link);

/**
* fixup_user_fault_nowait - manually resolve a user page fault without waiting
--
2.47.1