Re: [PATCH 26/28] KVM: x86/mmu: Zap only TDP MMU leafs in kvm_zap_gfn_range()

Ben Gardon
2021-11-23T19:58:39Z

On Fri, Nov 19, 2021 at 8:51 PM Sean Christopherson <seanjc@google.com> wrote:
>
> Zap only leaf SPTEs in the TDP MMU's zap_gfn_range(), and rename various
> functions according. When removing mappings for functional correctness
> (except for the stupid VFIO GPU passthrough memslots bug), zapping the
> leaf SPTEs is sufficient as the paging structures themselves do not point
> at guest memory and do not directly impact the final translation (in the
> TDP MMU).
>
> Note, this aligns the TDP MMU with the legacy/full MMU, which zaps only
> the rmaps, a.k.a. leaf SPTEs, in kvm_zap_gfn_range() and
> kvm_unmap_gfn_range().
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Ben Gardon <bgardon@google.com>

> ---
> arch/x86/kvm/mmu/mmu.c | 4 ++--
> arch/x86/kvm/mmu/tdp_mmu.c | 41 ++++++++++----------------------------
> arch/x86/kvm/mmu/tdp_mmu.h | 8 +-------
> 3 files changed, 14 insertions(+), 39 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index e3cd330c9532..ef689b8bab12 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -5796,8 +5796,8 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
>
> if (is_tdp_mmu_enabled(kvm)) {
> for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++)
> - flush = kvm_tdp_mmu_zap_gfn_range(kvm, i, gfn_start,
> - gfn_end, flush);
> + flush = kvm_tdp_mmu_zap_leafs(kvm, i, gfn_start,
> + gfn_end, true, flush);
> }
>
> if (flush)
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 926e92473e92..79a52717916c 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -834,10 +834,8 @@ bool kvm_tdp_mmu_zap_sp(struct kvm *kvm, struct kvm_mmu_page *sp)
> }
>
> /*
> - * 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 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
> @@ -845,18 +843,11 @@ bool kvm_tdp_mmu_zap_sp(struct kvm *kvm, struct kvm_mmu_page *sp)
> * the caller must ensure it does not supply too large a GFN range, or the
> * operation can cause a soft lockup.
> */
> -static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
> - gfn_t start, gfn_t end, bool can_yield, bool flush)
> +static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root,
> + gfn_t start, gfn_t end, bool can_yield, bool flush)
> {
> - bool zap_all = (start == 0 && end >= tdp_mmu_max_gfn_host());
> struct tdp_iter iter;
>
> - /*
> - * No need to try to step down in the iterator when zapping all SPTEs,
> - * zapping the top-level non-leaf SPTEs will recurse on their children.
> - */
> - int min_level = zap_all ? root->role.level : PG_LEVEL_4K;
> -
> end = min(end, tdp_mmu_max_gfn_host());
>
> lockdep_assert_held_write(&kvm->mmu_lock);
> @@ -864,24 +855,14 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
> rcu_read_lock();
>
> for_each_tdp_pte_min_level(iter, root->spt, root->role.level,
> - min_level, start, end) {
> + PG_LEVEL_4K, start, end) {
> if (can_yield &&
> tdp_mmu_iter_cond_resched(kvm, &iter, flush, false)) {
> flush = false;
> continue;
> }
>
> - if (!is_shadow_present_pte(iter.old_spte))
> - continue;
> -
> - /*
> - * If this is a non-last-level SPTE that covers a larger range
> - * than should be zapped, continue, and zap the mappings at a
> - * lower level, except when zapping all SPTEs.
> - */
> - if (!zap_all &&
> - (iter.gfn < start ||
> - iter.gfn + KVM_PAGES_PER_HPAGE(iter.level) > end) &&
> + if (!is_shadow_present_pte(iter.old_spte) ||
> !is_last_spte(iter.old_spte, iter.level))
> continue;
>
> @@ -899,13 +880,13 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
> * SPTEs have been cleared and a TLB flush is needed before releasing the
> * MMU lock.
> */
> -bool __kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, int as_id, gfn_t start,
> - gfn_t end, bool can_yield, bool flush)
> +bool kvm_tdp_mmu_zap_leafs(struct kvm *kvm, int as_id, gfn_t start, gfn_t end,
> + bool can_yield, bool flush)
> {
> struct kvm_mmu_page *root;
>
> for_each_tdp_mmu_root_yield_safe(kvm, root, as_id, false)
> - flush = zap_gfn_range(kvm, root, start, end, can_yield, flush);
> + flush = tdp_mmu_zap_leafs(kvm, root, start, end, can_yield, false);
>
> return flush;
> }
> @@ -1147,8 +1128,8 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> bool kvm_tdp_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range,
> bool flush)
> {
> - return __kvm_tdp_mmu_zap_gfn_range(kvm, range->slot->as_id, range->start,
> - range->end, range->may_block, flush);
> + return kvm_tdp_mmu_zap_leafs(kvm, range->slot->as_id, range->start,
> + range->end, range->may_block, flush);
> }
>
> typedef bool (*tdp_handler_t)(struct kvm *kvm, struct tdp_iter *iter,
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
> index 8ad1717f4a1d..6e7c32170608 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.h
> +++ b/arch/x86/kvm/mmu/tdp_mmu.h
> @@ -24,14 +24,8 @@ __must_check static inline bool kvm_tdp_mmu_get_root(struct kvm_mmu_page *root)
> void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root,
> bool shared);
>
> -bool __kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, int as_id, gfn_t start,
> +bool kvm_tdp_mmu_zap_leafs(struct kvm *kvm, int as_id, gfn_t start,
> gfn_t end, bool can_yield, bool flush);
> -static inline bool kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, int as_id,
> - gfn_t start, gfn_t end, bool flush)
> -{
> - return __kvm_tdp_mmu_zap_gfn_range(kvm, as_id, start, end, true, flush);
> -}
> -
> bool kvm_tdp_mmu_zap_sp(struct kvm *kvm, struct kvm_mmu_page *sp);
> void kvm_tdp_mmu_zap_all(struct kvm *kvm);
> void kvm_tdp_mmu_invalidate_all_roots(struct kvm *kvm,
> --
> 2.34.0.rc2.393.gf8c9666880-goog
>