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Message-ID: <87lewuo4ge.fsf@redhat.com>
Date: Mon, 28 Mar 2022 10:40:17 +0200
From: Vitaly Kuznetsov <vkuznets@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>
Cc: Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, Ben Gardon <bgardon@...gle.com>
Subject: Re: [PATCH] KVM: x86/mmu: Zap only TDP MMU leafs in zap range and
mmu_notifier unmap
Sean Christopherson <seanjc@...gle.com> 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 <vkuznets@...hat.com>
> Cc: Ben Gardon <bgardon@...gle.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
> 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
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