Re: [PATCH v3 10/14] KVM: arm64: Implement KVM_PRE_FAULT_MEMORY

On Wed, Sep 23, 2026 at 12:18:10PM +0100, Fuad Tabba wrote:

Hi Lorenzo,

On Tue, 22 Sep 2026 15:18:04 +0100, "Lorenzo Stoakes (ARM)"
[off-list ref] wrote:
[...]

quoted

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c

[...]

quoted

+static long __pre_fault_s2(struct kvm_s2_mmu *mmu, struct kvm_vcpu *vcpu,
+                           gpa_t gpa, struct kvm_memory_slot *memslot, s8 level)

[...]

quoted

+        if (is_gmem)
+                ret = gmem_abort(&s2fd, &result);
+        else
+                ret = user_mem_abort(&s2fd, &result);

When kvm_gmem_get_pfn() fails, gmem_abort() calls
kvm_prepare_memory_fault_exit() before returning, which on this path
writes vcpu->run's exit_reason and memory_fault fields outside
KVM_RUN. If that happens on a vCPU between its KVM_EXIT_MMIO and its
next KVM_RUN, kvm_arch_vcpu_ioctl_run() reads KVM_EXIT_MEMORY_FAULT
instead, skips kvm_handle_mmio_return(), and the guest repeats the
access. Could gmem_abort() skip that exit when result is set?
user_mem_abort() never writes kvm_run.

Ack yeah we shouldn't be updating vcpu->run like that in that case, will
update to avoid doing that in v4.

Cheers,
/fuad

--
Cheers, Lorenzo