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    SubjectRe: [Patch v3 6/7] KVM: x86/mmu: Remove handle_changed_spte_dirty_log()
    On Fri, Feb 10, 2023 at 05:46:25PM -0800, Vipin Sharma wrote:
    > Remove handle_changed_spte_dirty_log() as there is no code flow which
    > sets 4KiB SPTE writable and hit this path. This function marks the page
    > dirty in a memslot only if new SPTE is 4KiB in size and writable.
    >
    > Current users of handle_changed_spte_dirty_log() are:
    > 1. set_spte_gfn() - Create only non writable SPTEs.
    > 2. write_protect_gfn() - Change an SPTE to non writable.
    > 3. zap leaf and roots APIs - Everything is 0.
    > 4. handle_removed_pt() - Sets SPTEs to REMOVED_SPTE
    > 5. tdp_mmu_link_sp() - Makes non leaf SPTEs.
    >
    > There is also no path which creates a writable 4KiB without going
    > through make_spte() and this functions takes care of marking SPTE dirty
    > in the memslot if it is PT_WRITABLE.
    >
    > Signed-off-by: Vipin Sharma <vipinsh@google.com>

    Aside from the comment suggestion,

    Reviewed-by: David Matlack <dmatlack@google.com>

    > ---
    > arch/x86/kvm/mmu/tdp_mmu.c | 22 ----------------------
    > 1 file changed, 22 deletions(-)
    >
    > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
    > index e50e869bf879..0c031319e901 100644
    > --- a/arch/x86/kvm/mmu/tdp_mmu.c
    > +++ b/arch/x86/kvm/mmu/tdp_mmu.c
    > @@ -345,24 +345,6 @@ static void handle_changed_spte_acc_track(u64 old_spte, u64 new_spte, int level)
    > kvm_set_pfn_accessed(spte_to_pfn(old_spte));
    > }
    >
    > -static void handle_changed_spte_dirty_log(struct kvm *kvm, int as_id, gfn_t gfn,
    > - u64 old_spte, u64 new_spte, int level)
    > -{
    > - bool pfn_changed;
    > - struct kvm_memory_slot *slot;
    > -
    > - if (level > PG_LEVEL_4K)
    > - return;
    > -
    > - pfn_changed = spte_to_pfn(old_spte) != spte_to_pfn(new_spte);
    > -
    > - if ((!is_writable_pte(old_spte) || pfn_changed) &&
    > - is_writable_pte(new_spte)) {
    > - slot = __gfn_to_memslot(__kvm_memslots(kvm, as_id), gfn);
    > - mark_page_dirty_in_slot(kvm, slot, gfn);
    > - }
    > -}
    > -
    > static void tdp_account_mmu_page(struct kvm *kvm, struct kvm_mmu_page *sp)
    > {
    > kvm_account_pgtable_pages((void *)sp->spt, +1);
    > @@ -614,8 +596,6 @@ static void handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
    > __handle_changed_spte(kvm, as_id, gfn, old_spte, new_spte, level,
    > shared);
    > handle_changed_spte_acc_track(old_spte, new_spte, level);
    > - handle_changed_spte_dirty_log(kvm, as_id, gfn, old_spte,
    > - new_spte, level);

    Please leave a comment somewhere in handle_changed_spte() to document
    why mark_page_dirty_in_slot() is not needed to help future readers and
    in case something changes in the future.

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