From: Jack Thomson jackabt@amazon.com

Enable the pre_fault_memory_test to run on arm64 by making it work with different guest page sizes and testing multiple guest configurations.

Update the test_assert to compare against the UCALL_EXIT_REASON, for portability, as arm64 exits with KVM_EXIT_MMIO while x86 uses KVM_EXIT_IO.

Signed-off-by: Jack Thomson jackabt@amazon.com --- tools/testing/selftests/kvm/Makefile.kvm | 1 + .../selftests/kvm/pre_fault_memory_test.c | 78 ++++++++++++++----- 2 files changed, 58 insertions(+), 21 deletions(-)

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm index 148d427ff24b..0ddd8db60197 100644 --- a/tools/testing/selftests/kvm/Makefile.kvm +++ b/tools/testing/selftests/kvm/Makefile.kvm @@ -183,6 +183,7 @@ TEST_GEN_PROGS_arm64 += memslot_perf_test TEST_GEN_PROGS_arm64 += mmu_stress_test TEST_GEN_PROGS_arm64 += rseq_test TEST_GEN_PROGS_arm64 += steal_time +TEST_GEN_PROGS_arm64 += pre_fault_memory_test

TEST_GEN_PROGS_s390 = $(TEST_GEN_PROGS_COMMON) TEST_GEN_PROGS_s390 += s390/memop diff --git a/tools/testing/selftests/kvm/pre_fault_memory_test.c b/tools/testing/selftests/kvm/pre_fault_memory_test.c index f04768c1d2e4..674931e7bb3a 100644 --- a/tools/testing/selftests/kvm/pre_fault_memory_test.c +++ b/tools/testing/selftests/kvm/pre_fault_memory_test.c @@ -11,19 +11,29 @@ #include <kvm_util.h> #include <processor.h> #include <pthread.h> +#include <guest_modes.h>

/* Arbitrarily chosen values */ -#define TEST_SIZE (SZ_2M + PAGE_SIZE) -#define TEST_NPAGES (TEST_SIZE / PAGE_SIZE) +#define TEST_BASE_SIZE SZ_2M #define TEST_SLOT 10

+/* Storage of test info to share with guest code */ +struct test_config { + int page_size; + uint64_t test_size; + uint64_t test_num_pages; +}; + +struct test_config test_config; + static void guest_code(uint64_t base_gpa) { volatile uint64_t val __used; + struct test_config *config = &test_config; int i;

- for (i = 0; i < TEST_NPAGES; i++) { - uint64_t *src = (uint64_t *)(base_gpa + i * PAGE_SIZE); + for (i = 0; i < config->test_num_pages; i++) { + uint64_t *src = (uint64_t *)(base_gpa + i * config->page_size);

val = *src; } @@ -159,11 +169,17 @@ static void pre_fault_memory(struct kvm_vcpu *vcpu, u64 base_gpa, u64 offset, KVM_PRE_FAULT_MEMORY, ret, vcpu->vm); }

-static void __test_pre_fault_memory(unsigned long vm_type, bool private) +struct test_params { + unsigned long vm_type; + bool private; +}; + +static void __test_pre_fault_memory(enum vm_guest_mode guest_mode, void *arg) { + struct test_params *p = arg; const struct vm_shape shape = { - .mode = VM_MODE_DEFAULT, - .type = vm_type, + .mode = guest_mode, + .type = p->vm_type, }; struct kvm_vcpu *vcpu; struct kvm_run *run; @@ -174,10 +190,17 @@ static void __test_pre_fault_memory(unsigned long vm_type, bool private) uint64_t guest_test_virt_mem; uint64_t alignment, guest_page_size;

+ pr_info("Testing guest mode: %s\n", vm_guest_mode_string(guest_mode)); + vm = vm_create_shape_with_one_vcpu(shape, &vcpu, guest_code);

- alignment = guest_page_size = vm_guest_mode_params[VM_MODE_DEFAULT].page_size; - guest_test_phys_mem = (vm->max_gfn - TEST_NPAGES) * guest_page_size; + guest_page_size = vm_guest_mode_params[guest_mode].page_size; + + test_config.page_size = guest_page_size; + test_config.test_size = TEST_BASE_SIZE + test_config.page_size; + test_config.test_num_pages = vm_calc_num_guest_pages(vm->mode, test_config.test_size); + + guest_test_phys_mem = (vm->max_gfn - test_config.test_num_pages) * test_config.page_size; #ifdef __s390x__ alignment = max(0x100000UL, guest_page_size); #else @@ -187,23 +210,31 @@ static void __test_pre_fault_memory(unsigned long vm_type, bool private) guest_test_virt_mem = guest_test_phys_mem & ((1ULL << (vm->va_bits - 1)) - 1);

vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS, - guest_test_phys_mem, TEST_SLOT, TEST_NPAGES, - private ? KVM_MEM_GUEST_MEMFD : 0); - virt_map(vm, guest_test_virt_mem, guest_test_phys_mem, TEST_NPAGES); + guest_test_phys_mem, TEST_SLOT, test_config.test_num_pages, + p->private ? KVM_MEM_GUEST_MEMFD : 0); + virt_map(vm, guest_test_virt_mem, guest_test_phys_mem, test_config.test_num_pages); + + if (p->private) + vm_mem_set_private(vm, guest_test_phys_mem, test_config.test_size); + pre_fault_memory(vcpu, guest_test_phys_mem, TEST_BASE_SIZE, 0, p->private); + /* Test pre-faulting over an already faulted range */ + pre_fault_memory(vcpu, guest_test_phys_mem, TEST_BASE_SIZE, 0, p->private); + pre_fault_memory(vcpu, guest_test_phys_mem + TEST_BASE_SIZE, + test_config.page_size * 2, test_config.page_size, p->private); + pre_fault_memory(vcpu, guest_test_phys_mem + test_config.test_size, + test_config.page_size, test_config.page_size, p->private);

- if (private) - vm_mem_set_private(vm, guest_test_phys_mem, TEST_SIZE); + vcpu_args_set(vcpu, 1, guest_test_virt_mem);

- pre_fault_memory(vcpu, guest_test_phys_mem, 0, SZ_2M, 0, private); - pre_fault_memory(vcpu, guest_test_phys_mem, SZ_2M, PAGE_SIZE * 2, PAGE_SIZE, private); - pre_fault_memory(vcpu, guest_test_phys_mem, TEST_SIZE, PAGE_SIZE, PAGE_SIZE, private); + /* Export the shared variables to the guest. */ + sync_global_to_guest(vm, test_config);

- vcpu_args_set(vcpu, 1, guest_test_virt_mem); vcpu_run(vcpu);

run = vcpu->run; - TEST_ASSERT(run->exit_reason == KVM_EXIT_IO, - "Wanted KVM_EXIT_IO, got exit reason: %u (%s)", + TEST_ASSERT(run->exit_reason == UCALL_EXIT_REASON, + "Wanted %s, got exit reason: %u (%s)", + exit_reason_str(UCALL_EXIT_REASON), run->exit_reason, exit_reason_str(run->exit_reason));

switch (get_ucall(vcpu, &uc)) { @@ -227,7 +258,12 @@ static void test_pre_fault_memory(unsigned long vm_type, bool private) return; }

- __test_pre_fault_memory(vm_type, private); + struct test_params p = { + .vm_type = vm_type, + .private = private, + }; + + for_each_guest_mode(__test_pre_fault_memory, &p); }

int main(int argc, char *argv[])

On Wed, Nov 19, 2025 at 03:49:09PM +0000, Jack Thomson wrote:

From: Jack Thomson jackabt@amazon.com

Enable the pre_fault_memory_test to run on arm64 by making it work with different guest page sizes and testing multiple guest configurations.

Update the test_assert to compare against the UCALL_EXIT_REASON, for portability, as arm64 exits with KVM_EXIT_MMIO while x86 uses KVM_EXIT_IO.

Signed-off-by: Jack Thomson jackabt@amazon.com

tools/testing/selftests/kvm/Makefile.kvm | 1 + .../selftests/kvm/pre_fault_memory_test.c | 78 ++++++++++++++----- 2 files changed, 58 insertions(+), 21 deletions(-)

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm index 148d427ff24b..0ddd8db60197 100644 --- a/tools/testing/selftests/kvm/Makefile.kvm +++ b/tools/testing/selftests/kvm/Makefile.kvm @@ -183,6 +183,7 @@ TEST_GEN_PROGS_arm64 += memslot_perf_test TEST_GEN_PROGS_arm64 += mmu_stress_test TEST_GEN_PROGS_arm64 += rseq_test TEST_GEN_PROGS_arm64 += steal_time +TEST_GEN_PROGS_arm64 += pre_fault_memory_test TEST_GEN_PROGS_s390 = $(TEST_GEN_PROGS_COMMON) TEST_GEN_PROGS_s390 += s390/memop diff --git a/tools/testing/selftests/kvm/pre_fault_memory_test.c b/tools/testing/selftests/kvm/pre_fault_memory_test.c index f04768c1d2e4..674931e7bb3a 100644 --- a/tools/testing/selftests/kvm/pre_fault_memory_test.c +++ b/tools/testing/selftests/kvm/pre_fault_memory_test.c @@ -11,19 +11,29 @@ #include <kvm_util.h> #include <processor.h> #include <pthread.h> +#include <guest_modes.h> /* Arbitrarily chosen values */ -#define TEST_SIZE (SZ_2M + PAGE_SIZE) -#define TEST_NPAGES (TEST_SIZE / PAGE_SIZE)

After applying on top of the base commit 8a4821412cf2c1429fffa07c012dd150f2edf78c, it does not build.

That TEST_NPAGES seems to still be used in delete_slot_worker(). I believe that's because of

"KVM: selftests: Test prefault memory during concurrent memslot removal"

Related issues with the pre_fault_memory() prototype.

Is that the correct base-commit or shall I use something else?

+#define TEST_BASE_SIZE SZ_2M #define TEST_SLOT 10

[...]

On Wed, 19 Nov 2025 15:49:08 +0000, Jack Thomson jackabt.amazon@gmail.com wrote:

From: Jack Thomson jackabt@amazon.com

Add kvm_arch_vcpu_pre_fault_memory() for arm64. The implementation hands off the stage-2 faulting logic to either gmem_abort() or user_mem_abort().

Add an optional page_size output parameter to user_mem_abort() to return the VMA page size, which is needed when pre-faulting.

Update the documentation to clarify x86 specific behaviour.

Signed-off-by: Jack Thomson jackabt@amazon.com

Documentation/virt/kvm/api.rst | 3 +- arch/arm64/kvm/Kconfig | 1 + arch/arm64/kvm/arm.c | 1 + arch/arm64/kvm/mmu.c | 73 ++++++++++++++++++++++++++++++++-- 4 files changed, 73 insertions(+), 5 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 57061fa29e6a..30872d080511 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -6493,7 +6493,8 @@ Errors: KVM_PRE_FAULT_MEMORY populates KVM's stage-2 page tables used to map memory for the current vCPU state. KVM maps memory as if the vCPU generated a stage-2 read page fault, e.g. faults in memory as needed, but doesn't break -CoW. However, KVM does not mark any newly created stage-2 PTE as Accessed. +CoW. However, on x86, KVM does not mark any newly created stage-2 PTE as +Accessed. In the case of confidential VM types where there is an initial set up of private guest memory before the guest is 'finalized'/measured, this ioctl diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig index 4f803fd1c99a..6872aaabe16c 100644 --- a/arch/arm64/kvm/Kconfig +++ b/arch/arm64/kvm/Kconfig @@ -25,6 +25,7 @@ menuconfig KVM select HAVE_KVM_CPU_RELAX_INTERCEPT select KVM_MMIO select KVM_GENERIC_DIRTYLOG_READ_PROTECT

• select KVM_GENERIC_PRE_FAULT_MEMORY select VIRT_XFER_TO_GUEST_WORK select KVM_VFIO select HAVE_KVM_DIRTY_RING_ACQ_REL

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index 870953b4a8a7..88c5dc2b4ee8 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -327,6 +327,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) case KVM_CAP_IRQFD_RESAMPLE: case KVM_CAP_COUNTER_OFFSET: case KVM_CAP_ARM_WRITABLE_IMP_ID_REGS:

• case KVM_CAP_PRE_FAULT_MEMORY: r = 1;

How does with pKVM, where the host is not in charge of dealing with stage-2?

break;

case KVM_CAP_SET_GUEST_DEBUG2: diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index 7cc964af8d30..cba09168fc6d 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c @@ -1599,8 +1599,8 @@ static int gmem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, struct kvm_s2_trans *nested,

• 	  struct kvm_memory_slot *memslot, unsigned long hva,
  

• 	  bool fault_is_perm)
  

• 	  struct kvm_memory_slot *memslot, long *page_size,
  

Why is page_size a signed type? A page size is never negative.

• 	  unsigned long hva, bool fault_is_perm)
  

I really wish we'd stop adding parameters to this function, as it has long stopped being readable. It would make a lot more sense if we passed a descriptor for the fault, containing the ipa, hva, memslot and fault type.

{ int ret = 0; bool topup_memcache; @@ -1878,6 +1878,9 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, kvm_release_faultin_page(kvm, page, !!ret, writable); kvm_fault_unlock(kvm);

• if (page_size)

• *page_size = vma_pagesize;
  

• /* Mark the page dirty only if the fault is handled successfully */ if (writable && !ret) mark_page_dirty_in_slot(kvm, memslot, gfn);

@@ -2080,8 +2083,8 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu) ret = gmem_abort(vcpu, fault_ipa, nested, memslot, esr_fsc_is_permission_fault(esr)); else

• ret = user_mem_abort(vcpu, fault_ipa, nested, memslot, hva,
  

• 		     esr_fsc_is_permission_fault(esr));
  

• ret = user_mem_abort(vcpu, fault_ipa, nested, memslot, NULL,
  

• 		     hva, esr_fsc_is_permission_fault(esr));
  

  if (ret == 0) ret = 1;

out: @@ -2457,3 +2460,65 @@ void kvm_toggle_cache(struct kvm_vcpu *vcpu, bool was_enabled) trace_kvm_toggle_cache(*vcpu_pc(vcpu), was_enabled, now_enabled); }

+long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu,

• 		    struct kvm_pre_fault_memory *range)
  

+{

• int ret, idx;
• hva_t hva;
• phys_addr_t end;
• struct kvm_memory_slot *memslot;
• struct kvm_vcpu_fault_info stored_fault, *fault_info;
• long page_size = PAGE_SIZE;
• phys_addr_t ipa = range->gpa;
• gfn_t gfn = gpa_to_gfn(range->gpa);

nit: Please order this in a more readable way, preferably with long line first.

• idx = srcu_read_lock(&vcpu->kvm->srcu);

??? Aren't we already guaranteed to be under the SRCU read lock?

• if (ipa >= kvm_phys_size(vcpu->arch.hw_mmu)) {

• ret = -ENOENT;
  

• goto out_unlock;
  

• }
• memslot = gfn_to_memslot(vcpu->kvm, gfn);
• if (!memslot) {

• ret = -ENOENT;
  

• goto out_unlock;
  

• }
• fault_info = &vcpu->arch.fault;
• stored_fault = *fault_info;

If this is a vcpu ioctl, can the fault information be actually valid while userspace is issuing an ioctl? Wouldn't that mean that we are exiting to userspace in the middle of handling an exception?

• /* Generate a synthetic abort for the pre-fault address */
• fault_info->esr_el2 = ESR_ELx_EC_DABT_LOW;
• fault_info->esr_el2 &= ~ESR_ELx_ISV;

You are constructing this from scratch. How can ISV be set?

• fault_info->esr_el2 |= ESR_ELx_FSC_FAULT_L(KVM_PGTABLE_LAST_LEVEL);
• fault_info->hpfar_el2 = HPFAR_EL2_NS |

• FIELD_PREP(HPFAR_EL2_FIPA, ipa >> 12);
  

• if (kvm_slot_has_gmem(memslot)) {

• ret = gmem_abort(vcpu, ipa, NULL, memslot, false);
  

• } else {

• hva = gfn_to_hva_memslot_prot(memslot, gfn, NULL);
  

• if (kvm_is_error_hva(hva)) {
  

• 	ret = -EFAULT;
  

• 	goto out;
  

• }
  

• ret = user_mem_abort(vcpu, ipa, NULL, memslot, &page_size, hva,
  

• 		     false);
  

• }
• if (ret < 0)

• goto out;
  

• end = (range->gpa & ~(page_size - 1)) + page_size;

This suspiciously looks like one of the __ALIGN_KERNEL* macros.

• ret = min(range->size, end - range->gpa);

+out:

• *fault_info = stored_fault;

+out_unlock:

• srcu_read_unlock(&vcpu->kvm->srcu, idx);
• return ret;

+}

Thanks,

M.