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

[Lorenzo Stoakes (ARM)]

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)"
> <ljs at kernel.org> wrote:
> [...]
> > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> [...]
> > +static long __pre_fault_s2(struct kvm_s2_mmu *mmu, struct kvm_vcpu *vcpu,
> > +                           gpa_t gpa, struct kvm_memory_slot *memslot, s8 level)
> [...]
> > +        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