[PATCH] KVM: riscv: Implement kvm_arch_pre_fault_allowed()

[PATCH] KVM: riscv: Implement kvm_arch_pre_fault_allowed()

[Sasha Levin]

Commit caa63620f9e3 ("KVM: Allow architectures to disallow pre-fault")
requires every architecture that selects KVM_GENERIC_PRE_FAULT_MEMORY to
implement kvm_arch_pre_fault_allowed(), and there is no generic default.

Commit e8b32e377951 ("KVM: riscv: Implement KVM_PRE_FAULT_MEMORY") was
written before that hook existed, so it selects the option without
implementing the hook. With both commits in the same tree, riscv builds
with KVM enabled fail to link:

  ld.lld: error: undefined symbol: kvm_arch_pre_fault_allowed
  >>> referenced by kvm_main.c
  >>>               virt/kvm/kvm_main.o:(kvm_vcpu_pre_fault_memory) in archive vmlinux.a

The riscv implementation does not refuse pre-faulting in any state, so
return 0 to keep its current behaviour.

Fixes: e8b32e377951 ("KVM: riscv: Implement KVM_PRE_FAULT_MEMORY")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
Paolo, this is needed when kvm-riscv-7.4-1 is merged into kvm/next.
Feel free to squash it into the merge instead.

Mark, next-20261022 already fails to link, so linux-next needs this on
top of the kvm-riscv merge.

Build-tested with a riscv tinyconfig plus KVM=y on next-20261022 and on
kvm/next with kvm-riscv-7.4-1 merged. Not runtime tested.

 arch/riscv/kvm/mmu.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
index e8673cfa69668..738d9ee1eac9d 100644
--- a/arch/riscv/kvm/mmu.c
+++ b/arch/riscv/kvm/mmu.c
@@ -754,6 +754,11 @@ int kvm_riscv_mmu_map(struct kvm_vcpu *vcpu, struct kvm_memory_slot *memslot,
 	return ret;
 }
 
+int kvm_arch_pre_fault_allowed(struct kvm_vcpu *vcpu)
+{
+	return 0;
+}
+
 long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu,
 				    struct kvm_pre_fault_memory *range)
 {
-- 
2.53.0

Re: [PATCH] KVM: riscv: Implement kvm_arch_pre_fault_allowed()

[Paolo Bonzini]

On Thu, Oct 22, 2026 at 4:42 PM Sasha Levin <sashal@kernel.org> wrote:
>
> Commit caa63620f9e3 ("KVM: Allow architectures to disallow pre-fault")
> requires every architecture that selects KVM_GENERIC_PRE_FAULT_MEMORY to
> implement kvm_arch_pre_fault_allowed(), and there is no generic default.
>
> Commit e8b32e377951 ("KVM: riscv: Implement KVM_PRE_FAULT_MEMORY") was
> written before that hook existed, so it selects the option without
> implementing the hook. With both commits in the same tree, riscv builds
> with KVM enabled fail to link:
>
>   ld.lld: error: undefined symbol: kvm_arch_pre_fault_allowed
>   >>> referenced by kvm_main.c
>   >>>               virt/kvm/kvm_main.o:(kvm_vcpu_pre_fault_memory) in archive vmlinux.a
>
> The riscv implementation does not refuse pre-faulting in any state, so
> return 0 to keep its current behaviour.
>
> Fixes: e8b32e377951 ("KVM: riscv: Implement KVM_PRE_FAULT_MEMORY")
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> Paolo, this is needed when kvm-riscv-7.4-1 is merged into kvm/next.
> Feel free to squash it into the merge instead.

Yup, done. It will be in tomorrow's linux-next via kvm/next.

I'll send the RISC-V PR to Linus next week, so if he complains it will
be there in kvm/next ready for 7.5. :)

Paolo