On Mon, Nov 22, 2021 at 10:53 AM Ben Gardon <bgardon@xxxxxxxxxx> wrote:
>
> On Fri, Nov 19, 2021 at 3:58 PM David Matlack <dmatlack@xxxxxxxxxx> wrote:
> >
> > Factor out the logic to atomically replace an SPTE with an SPTE that
> > points to a new page table. This will be used in a follow-up commit to
> > split a large page SPTE into one level lower.
> >
> > Signed-off-by: David Matlack <dmatlack@xxxxxxxxxx>
> > ---
> > arch/x86/kvm/mmu/tdp_mmu.c | 53 ++++++++++++++++++++++++++------------
> > 1 file changed, 37 insertions(+), 16 deletions(-)
> >
> > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> > index cc9fe33c9b36..9ee3f4f7fdf5 100644
> > --- a/arch/x86/kvm/mmu/tdp_mmu.c
> > +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> > @@ -945,6 +945,39 @@ static int tdp_mmu_map_handle_target_level(struct kvm_vcpu *vcpu,
> > return ret;
> > }
> >
> > +/*
> > + * tdp_mmu_install_sp_atomic - Atomically replace the given spte with an
> > + * spte pointing to the provided page table.
> > + *
> > + * @kvm: kvm instance
> > + * @iter: a tdp_iter instance currently on the SPTE that should be set
> > + * @sp: The new TDP page table to install.
> > + * @account_nx: True if this page table is being installed to split a
> > + * non-executable huge page.
> > + *
> > + * Returns: True if the new page table was installed. False if spte being
> > + * replaced changed, causing the atomic compare-exchange to fail.
> > + * If this function returns false the sp will be freed before
> > + * returning.
> > + */
> > +static bool tdp_mmu_install_sp_atomic(struct kvm *kvm,
> > + struct tdp_iter *iter,
> > + struct kvm_mmu_page *sp,
> > + bool account_nx)
> > +{
> > + u64 spte;
> > +
> > + spte = make_nonleaf_spte(sp->spt, !shadow_accessed_mask);
> > +
> > + if (tdp_mmu_set_spte_atomic(kvm, iter, spte)) {
> > + tdp_mmu_link_page(kvm, sp, account_nx);
> > + return true;
> > + } else {
> > + tdp_mmu_free_sp(sp);
> > + return false;
> > + }
> > +}
> > +
> > /*
> > * Handle a TDP page fault (NPT/EPT violation/misconfiguration) by installing
> > * page tables and SPTEs to translate the faulting guest physical address.
> > @@ -954,8 +987,6 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> > struct kvm_mmu *mmu = vcpu->arch.mmu;
> > struct tdp_iter iter;
> > struct kvm_mmu_page *sp;
> > - u64 *child_pt;
> > - u64 new_spte;
> > int ret;
> >
> > kvm_mmu_hugepage_adjust(vcpu, fault);
> > @@ -983,6 +1014,9 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> > }
> >
> > if (!is_shadow_present_pte(iter.old_spte)) {
> > + bool account_nx = fault->huge_page_disallowed &&
> > + fault->req_level >= iter.level;
> > +
> > /*
> > * If SPTE has been frozen by another thread, just
> > * give up and retry, avoiding unnecessary page table
> > @@ -992,21 +1026,8 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> > break;
> >
> > sp = alloc_tdp_mmu_page(vcpu, iter.gfn, iter.level - 1);
> > - child_pt = sp->spt;
> > -
> > - new_spte = make_nonleaf_spte(child_pt,
> > - !shadow_accessed_mask);
> > -
> > - if (tdp_mmu_set_spte_atomic(vcpu->kvm, &iter, new_spte)) {
> > - tdp_mmu_link_page(vcpu->kvm, sp,
> > - fault->huge_page_disallowed &&
> > - fault->req_level >= iter.level);
> > -
> > - trace_kvm_mmu_get_page(sp, true);
>
> This refactoring drops this trace point. Is that intentional?
Yes it was intentional, but I forgot to describe it in the commit
message. Good catch.
This tracepoint is redundant with the one in alloc_tdp_mmu_page().
I'll update the commit message for v1.
>
>
> > - } else {
> > - tdp_mmu_free_sp(sp);
> > + if (!tdp_mmu_install_sp_atomic(vcpu->kvm, &iter, sp, account_nx))
> > break;
> > - }
> > }
> > }
> >
> > --
> > 2.34.0.rc2.393.gf8c9666880-goog
> >
