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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id g16-20020a05600c4ed000b0038ceb0b21b4sm9028325wmq.24.2022.03.28.01.40.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Mar 2022 01:40:18 -0700 (PDT) From: Vitaly Kuznetsov To: Sean Christopherson , Paolo Bonzini Cc: Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Ben Gardon Subject: Re: [PATCH] KVM: x86/mmu: Zap only TDP MMU leafs in zap range and mmu_notifier unmap In-Reply-To: <20220325230348.2587437-1-seanjc@google.com> References: <20220325230348.2587437-1-seanjc@google.com> Date: Mon, 28 Mar 2022 10:40:17 +0200 Message-ID: <87lewuo4ge.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Sean Christopherson writes: > Re-introduce zapping only leaf SPTEs in kvm_zap_gfn_range() and > kvm_tdp_mmu_unmap_gfn_range(), this time without losing a pending TLB > flush when processing multiple roots (including nested TDP shadow roots). > Dropping the TLB flush resulted in random crashes when running Hyper-V > Server 2019 in a guest with KSM enabled in the host (or any source of > mmu_notifier invalidations, KSM is just the easiest to force). > > This effectively revert commits 873dd122172f8cce329113cfb0dfe3d2344d80c0 > and fcb93eb6d09dd302cbef22bd95a5858af75e4156, and thus restores commit > cf3e26427c08ad9015956293ab389004ac6a338e, plus this delta on top: > > bool kvm_tdp_mmu_zap_leafs(struct kvm *kvm, int as_id, gfn_t start, gfn_t end, > struct kvm_mmu_page *root; > > for_each_tdp_mmu_root_yield_safe(kvm, root, as_id) > - flush = tdp_mmu_zap_leafs(kvm, root, start, end, can_yield, false); > + flush = tdp_mmu_zap_leafs(kvm, root, start, end, can_yield, flush); > > return flush; > } > I confirm this fixes the issue I was seeing, thanks! Tested-by: Vitaly Kuznetsov > Cc: Ben Gardon > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/mmu/mmu.c | 4 +-- > arch/x86/kvm/mmu/tdp_mmu.c | 57 +++++++++++--------------------------- > arch/x86/kvm/mmu/tdp_mmu.h | 8 +----- > 3 files changed, 19 insertions(+), 50 deletions(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 1361eb4599b4..a7cb877f3784 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -5842,8 +5842,8 @@ 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 b3b6426725d4..c4333efb9e9c 100644 > --- a/arch/x86/kvm/mmu/tdp_mmu.c > +++ b/arch/x86/kvm/mmu/tdp_mmu.c > @@ -906,10 +906,8 @@ 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 > @@ -917,44 +915,25 @@ 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. > - * Do not do it above the 1GB level, to avoid making tdp_mmu_set_spte's > - * recursion too expensive and allow yielding. > - */ > - int min_level = zap_all ? PG_LEVEL_1G : PG_LEVEL_4K; > - > end = min(end, tdp_mmu_max_gfn_host()); > > lockdep_assert_held_write(&kvm->mmu_lock); > > rcu_read_lock(); > > - for_each_tdp_pte_min_level(iter, root, min_level, start, end) { > + for_each_tdp_pte_min_level(iter, root, 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; > > @@ -962,17 +941,13 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, > flush = true; > } > > + rcu_read_unlock(); > + > /* > - * Need to flush before releasing RCU. TODO: do it only if intermediate > - * page tables were zapped; there is no need to flush under RCU protection > - * if no 'struct kvm_mmu_page' is freed. > + * Because this flow zaps _only_ leaf SPTEs, the caller doesn't need > + * to provide RCU protection as no 'struct kvm_mmu_page' will be freed. > */ > - if (flush) > - kvm_flush_remote_tlbs_with_address(kvm, start, end - start); > - > - rcu_read_unlock(); > - > - return false; > + return flush; > } > > /* > @@ -981,13 +956,13 @@ 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) > - flush = zap_gfn_range(kvm, root, start, end, can_yield, flush); > + flush = tdp_mmu_zap_leafs(kvm, root, start, end, can_yield, flush); > > return flush; > } > @@ -1235,8 +1210,8 @@ 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 5e5ef2576c81..54bc8118c40a 100644 > --- a/arch/x86/kvm/mmu/tdp_mmu.h > +++ b/arch/x86/kvm/mmu/tdp_mmu.h > @@ -15,14 +15,8 @@ __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); > > base-commit: 19164ad08bf668bca4f4bfbaacaa0a47c1b737a6 -- Vitaly