KVM, x86/mmu: Fix the comment around kvm_tdp_mmu_zap_leafs()

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2119111



commit 7edc3a68
Author: Kai Huang <kai.huang@intel.com>
Date:   Thu Jul 28 15:04:52 2022 +1200

    KVM, x86/mmu: Fix the comment around kvm_tdp_mmu_zap_leafs()

    Now kvm_tdp_mmu_zap_leafs() only zaps leaf SPTEs but not any non-root
    pages within that GFN range anymore, so the comment around it isn't
    right.

    Fix it by shifting the comment from tdp_mmu_zap_leafs() instead of
    duplicating it, as tdp_mmu_zap_leafs() is static and is only called by
    kvm_tdp_mmu_zap_leafs().

    Opportunistically tweak the blurb about SPTEs being cleared to (a) say
    "zapped" instead of "cleared" because "cleared" will be wrong if/when
    KVM allows a non-zero value for non-present SPTE (i.e. for Intel TDX),
    and (b) to clarify that a flush is needed if and only if a SPTE has been
    zapped since MMU lock was last acquired.

    Fixes: f47e5bbb ("KVM: x86/mmu: Zap only TDP MMU leafs in zap range and mmu_notifier unmap")
Suggested-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Kai Huang <kai.huang@intel.com>
    Message-Id: <20220728030452.484261-1-kai.huang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>

arch/x86/kvm/mmu/tdp_mmu.c

@@ -924,9 +924,6 @@ bool kvm_tdp_mmu_zap_sp(struct kvm *kvm, struct kvm_mmu_page *sp)
 }
 
 /*
- * Zap leafs SPTEs for the range of gfns, [start, end). Returns true if SPTEs
- * have been cleared and a TLB flush is needed before releasing the MMU lock.
- *
  * If can_yield is true, will release the MMU lock and reschedule if the
  * scheduler needs the CPU or there is contention on the MMU lock. If this
  * function cannot yield, it will not release the MMU lock or reschedule and
@@ -969,10 +966,9 @@ static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root,
 }
 
 /*
- * Tears down the mappings for the range of gfns, [start, end), and frees the
- * non-root pages mapping GFNs strictly within that range. Returns true if
- * SPTEs have been cleared and a TLB flush is needed before releasing the
- * MMU lock.
+ * Zap leaf SPTEs for the range of gfns, [start, end), for all roots. Returns
+ * true if a TLB flush is needed before releasing the MMU lock, i.e. if one or
+ * more SPTEs were zapped since the MMU lock was last acquired.
  */
 bool kvm_tdp_mmu_zap_leafs(struct kvm *kvm, int as_id, gfn_t start, gfn_t end,
 			   bool can_yield, bool flush)