On Wed, May 5, 2021 at 9:00 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxx>
Haha I was just about to add the same two comments. Besides those,
this patch looks good to me as well.
Reviewed-by: Ben Gardon <bgardon@xxxxxxxxxx>
>
>
> Side topic...
>
> Ben, does the TDP MMU intentionally not prefetch pages? If so, why not?
It does not currently prefetch pages, but there's no reason it
shouldn't. It simply hasn't been implemented yet.
>
> > Signed-off-by: Kai Huang <kai.huang@xxxxxxxxx>
> > ---
> > 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
> >
