Re: [PATCH 1/3] KVM: x86/mmu: Fix return value in tdp_mmu_map_handle_target_level()

[Sean Christopherson <seanjc@google.com>]

On Wed, May 05, 2021, Kai Huang wrote:
> Currently tdp_mmu_map_handle_target_level() returns 0, which is
> RET_PF_RETRY, when page fault is actually fixed.  This makes
> kvm_tdp_mmu_map() also return RET_PF_RETRY in this case, instead of
> RET_PF_FIXED.  Fix by initializing ret to RET_PF_FIXED.

Probably worth adding a blurb to call out that the bad return value is benign
since kvm_mmu_page_fault() resumes the guest on RET_PF_RETRY or RET_PF_FIXED.
And for good measure, a Fixes without stable@.

  Fixes: bb18842e2111 ("kvm: x86/mmu: Add TDP MMU PF handler")

Reviewed-by: Sean Christopherson <seanjc@google.com> 


Side topic...

Ben, does the TDP MMU intentionally not prefetch pages?  If so, why not?

> Signed-off-by: Kai Huang <kai.huang@intel.com>
> ---
>  arch/x86/kvm/mmu/tdp_mmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index ff0ae030004d..1cad4c9f7c34 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -905,7 +905,7 @@ static int tdp_mmu_map_handle_target_level(struct kvm_vcpu *vcpu, int write,
>  					  kvm_pfn_t pfn, bool prefault)
>  {
>  	u64 new_spte;
> -	int ret = 0;
> +	int ret = RET_PF_FIXED;
>  	int make_spte_ret = 0;
>  
>  	if (unlikely(is_noslot_pfn(pfn)))
> -- 
> 2.31.1
>