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Message-ID: <20251013151502.6679-2-jackabt.amazon@gmail.com>
Date: Mon, 13 Oct 2025 16:14:58 +0100
From: Jack Thomson <jackabt.amazon@...il.com>
To: maz@...nel.org,
oliver.upton@...ux.dev,
pbonzini@...hat.com
Cc: joey.gouly@....com,
suzuki.poulose@....com,
yuzenghui@...wei.com,
catalin.marinas@....com,
will@...nel.org,
shuah@...nel.org,
linux-arm-kernel@...ts.infradead.org,
kvmarm@...ts.linux.dev,
linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org,
isaku.yamahata@...el.com,
roypat@...zon.co.uk,
kalyazin@...zon.co.uk,
jackabt@...zon.com
Subject: [PATCH v2 1/4] KVM: arm64: Add pre_fault_memory implementation
From: Jack Thomson <jackabt@...zon.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@...zon.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 c17a87a0a5ac..9e8cc4eb505d 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6461,7 +6461,8 @@ 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 bff62e75d681..1ac0605f86cb 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 KVM_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 888f7c7abf54..65654a742864 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -322,6 +322,7 @@ 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;
break;
case KVM_CAP_SET_GUEST_DEBUG2:
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index a36426ccd9b5..82f122e4b08c 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1597,8 +1597,8 @@ 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,
+ unsigned long hva, bool fault_is_perm)
{
int ret = 0;
bool topup_memcache;
@@ -1871,6 +1871,9 @@ 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);
@@ -2069,8 +2072,8 @@ 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:
@@ -2446,3 +2449,65 @@ 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);
+
+ idx = srcu_read_lock(&vcpu->kvm->srcu);
+
+ 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;
+
+ /* Generate a synthetic abort for the pre-fault address */
+ fault_info->esr_el2 = FIELD_PREP(ESR_ELx_EC_MASK, ESR_ELx_EC_DABT_CUR);
+ fault_info->esr_el2 &= ~ESR_ELx_ISV;
+ 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;
+ ret = min(range->size, end - range->gpa);
+
+out:
+ *fault_info = stored_fault;
+out_unlock:
+ srcu_read_unlock(&vcpu->kvm->srcu, idx);
+ return ret;
+}
--
2.43.0
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