| Message ID | 20210112181041.356734-7-bgardon@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Allow parallel page faults with TDP MMU | expand |
On Tue, Jan 12, 2021, Ben Gardon wrote: > Skip setting SPTEs if no change is expected. > > Reviewed-by: Peter Feiner <pfeiner@google.com> > Nit on all of these, can you remove the extra newline between the Reviewed-by and SOB? > Signed-off-by: Ben Gardon <bgardon@google.com> > --- > arch/x86/kvm/mmu/tdp_mmu.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c > index 1987da0da66e..2650fa9fe066 100644 > --- a/arch/x86/kvm/mmu/tdp_mmu.c > +++ b/arch/x86/kvm/mmu/tdp_mmu.c > @@ -882,6 +882,9 @@ static bool wrprot_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, > !is_last_spte(iter.old_spte, iter.level)) > continue; > > + if (!(iter.old_spte & PT_WRITABLE_MASK)) Include the new check with the existing if statement? I think it makes sense to group all the checks on old_spte. > + continue; > + > new_spte = iter.old_spte & ~PT_WRITABLE_MASK; > > tdp_mmu_set_spte_no_dirty_log(kvm, &iter, new_spte); > @@ -1079,6 +1082,9 @@ static bool set_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, > if (!is_shadow_present_pte(iter.old_spte)) > continue; > > + if (iter.old_spte & shadow_dirty_mask) Same comment here. > + continue; > + Unrelated to this patch, but it got me looking at the code: shouldn't clear_dirty_pt_masked() clear the bit in @mask before checking whether or not the spte needs to be modified? That way the early break kicks in after sptes are checked, not necessarily written. E.g. diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index 2650fa9fe066..d8eeae910cbf 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -1010,21 +1010,21 @@ static void clear_dirty_pt_masked(struct kvm *kvm, struct kvm_mmu_page *root, !(mask & (1UL << (iter.gfn - gfn)))) continue; - if (wrprot || spte_ad_need_write_protect(iter.old_spte)) { - if (is_writable_pte(iter.old_spte)) - new_spte = iter.old_spte & ~PT_WRITABLE_MASK; - else - continue; - } else { - if (iter.old_spte & shadow_dirty_mask) - new_spte = iter.old_spte & ~shadow_dirty_mask; - else - continue; - } - - tdp_mmu_set_spte_no_dirty_log(kvm, &iter, new_spte); - mask &= ~(1UL << (iter.gfn - gfn)); + + if (wrprot || spte_ad_need_write_protect(iter.old_spte)) { + if (is_writable_pte(iter.old_spte)) + new_spte = iter.old_spte & ~PT_WRITABLE_MASK; + else + continue; + } else { + if (iter.old_spte & shadow_dirty_mask) + new_spte = iter.old_spte & ~shadow_dirty_mask; + else + continue; + } + + tdp_mmu_set_spte_no_dirty_log(kvm, &iter, new_spte); } } > new_spte = iter.old_spte | shadow_dirty_mask; > > tdp_mmu_set_spte(kvm, &iter, new_spte); > -- > 2.30.0.284.gd98b1dd5eaa7-goog >
On Wed, Jan 20, 2021 at 11:51 AM Sean Christopherson <seanjc@google.com> wrote: > > On Tue, Jan 12, 2021, Ben Gardon wrote: > > Skip setting SPTEs if no change is expected. > > > > Reviewed-by: Peter Feiner <pfeiner@google.com> > > > Nit on all of these, can you remove the extra newline between the Reviewed-by > and SOB? Yeah, that line is annoying. I'll make sure it's not there on future patches. > > > Signed-off-by: Ben Gardon <bgardon@google.com> > > --- > > arch/x86/kvm/mmu/tdp_mmu.c | 6 ++++++ > > 1 file changed, 6 insertions(+) > > > > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c > > index 1987da0da66e..2650fa9fe066 100644 > > --- a/arch/x86/kvm/mmu/tdp_mmu.c > > +++ b/arch/x86/kvm/mmu/tdp_mmu.c > > @@ -882,6 +882,9 @@ static bool wrprot_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, > > !is_last_spte(iter.old_spte, iter.level)) > > continue; > > > > + if (!(iter.old_spte & PT_WRITABLE_MASK)) > > Include the new check with the existing if statement? I think it makes sense to > group all the checks on old_spte. I agree that' s cleaner. I'll group the checks in the next patch set version. > > > + continue; > > + > > new_spte = iter.old_spte & ~PT_WRITABLE_MASK; > > > > tdp_mmu_set_spte_no_dirty_log(kvm, &iter, new_spte); > > @@ -1079,6 +1082,9 @@ static bool set_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, > > if (!is_shadow_present_pte(iter.old_spte)) > > continue; > > > > + if (iter.old_spte & shadow_dirty_mask) > > Same comment here. > > > + continue; > > + > > Unrelated to this patch, but it got me looking at the code: shouldn't > clear_dirty_pt_masked() clear the bit in @mask before checking whether or not > the spte needs to be modified? That way the early break kicks in after sptes > are checked, not necessarily written. E.g. > > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c > index 2650fa9fe066..d8eeae910cbf 100644 > --- a/arch/x86/kvm/mmu/tdp_mmu.c > +++ b/arch/x86/kvm/mmu/tdp_mmu.c > @@ -1010,21 +1010,21 @@ static void clear_dirty_pt_masked(struct kvm *kvm, struct kvm_mmu_page *root, > !(mask & (1UL << (iter.gfn - gfn)))) > continue; > > - if (wrprot || spte_ad_need_write_protect(iter.old_spte)) { > - if (is_writable_pte(iter.old_spte)) > - new_spte = iter.old_spte & ~PT_WRITABLE_MASK; > - else > - continue; > - } else { > - if (iter.old_spte & shadow_dirty_mask) > - new_spte = iter.old_spte & ~shadow_dirty_mask; > - else > - continue; > - } > - > - tdp_mmu_set_spte_no_dirty_log(kvm, &iter, new_spte); > - > mask &= ~(1UL << (iter.gfn - gfn)); > + > + if (wrprot || spte_ad_need_write_protect(iter.old_spte)) { > + if (is_writable_pte(iter.old_spte)) > + new_spte = iter.old_spte & ~PT_WRITABLE_MASK; > + else > + continue; > + } else { > + if (iter.old_spte & shadow_dirty_mask) > + new_spte = iter.old_spte & ~shadow_dirty_mask; > + else > + continue; > + } > + > + tdp_mmu_set_spte_no_dirty_log(kvm, &iter, new_spte); > } > } > Great point, that doesn't work as intended at all. I'll adopt your proposed fix and include it in a patch after this one in the next version of the series. > > > new_spte = iter.old_spte | shadow_dirty_mask; > > > > tdp_mmu_set_spte(kvm, &iter, new_spte); > > -- > > 2.30.0.284.gd98b1dd5eaa7-goog > >
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index 1987da0da66e..2650fa9fe066 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -882,6 +882,9 @@ static bool wrprot_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, !is_last_spte(iter.old_spte, iter.level)) continue; + if (!(iter.old_spte & PT_WRITABLE_MASK)) + continue; + new_spte = iter.old_spte & ~PT_WRITABLE_MASK; tdp_mmu_set_spte_no_dirty_log(kvm, &iter, new_spte); @@ -1079,6 +1082,9 @@ static bool set_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, if (!is_shadow_present_pte(iter.old_spte)) continue; + if (iter.old_spte & shadow_dirty_mask) + continue; + new_spte = iter.old_spte | shadow_dirty_mask; tdp_mmu_set_spte(kvm, &iter, new_spte);