Re: [PATCH 3/3] KVM: arm64: Do a KVM_EXIT_MEMORY_FAULT when stage-2 fault handler EFAULTs

[Oliver Upton <oliver.upton@linux.dev>]

On Fri, Aug 02, 2024 at 10:40:31PM +0000, Anish Moorthy wrote:
> Right now userspace just gets a bare EFAULT when the stage-2 fault
> handler fails to fault in the relevant page. Set up a memory fault exit
> when this happens, which at the very least eases debugging and might
> also let userspace decide on/take some specific action other than
> crashing the VM.

There are several other 'bare' EFAULTs remaining (unexpected fault
context, failed vma_lookup(), nested PTW), so the patch doesn't exactly
match the shortlog.

Is there a reason why those are unaddressed? In any case, it doesn't
hurt to be unambiguous in the shortlog if we're only focused on this single
error condition, e.g.

  KVM: arm64: Do a memory fault exit if __gfn_to_pfn_memslot() fails

> Signed-off-by: Anish Moorthy <amoorthy@google.com>
> ---
>  arch/arm64/kvm/mmu.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 6981b1bc0946..52b4f8e648fb 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1568,8 +1568,11 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  		kvm_send_hwpoison_signal(hva, vma_shift);
>  		return 0;
>  	}
> -	if (is_error_noslot_pfn(pfn))
> +	if (is_error_noslot_pfn(pfn)) {
> +		kvm_prepare_memory_fault_exit(vcpu, fault_ipa, vma_pagesize,
> +					      write_fault, exec_fault, false);
>  		return -EFAULT;
> +	}
>  
>  	if (kvm_is_device_pfn(pfn)) {
>  		/*
> -- 
> 2.46.0.rc2.264.g509ed76dc8-goog
> 

-- 
Thanks,
Oliver