From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f202.google.com (mail-pl1-f202.google.com [209.85.214.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 786482E0D8 for ; Thu, 15 Jun 2023 18:26:53 +0000 (UTC) Received: by mail-pl1-f202.google.com with SMTP id d9443c01a7336-1b500efc982so15378445ad.2 for ; Thu, 15 Jun 2023 11:26:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1686853612; x=1689445612; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=v5j0wCZPnfsM4/SjEwwVDfexZdOw0uK6iqseA0HQUzE=; b=pVetr2jEMF5lF1mCTvADonXqP6bFE0nxsdmxOn0ASTw2/bFTnBCX3GM5/ND7idJYcK WLJ9v5Jtgv7YkQ2t1A7zr6BtWjGAUd3nGNd07s8rKjBzK87V1SPxXbBBFz/A0h4/TJ+6 PGmBMXeXE9iwEFyxsQoXFCV8sBkm29Ah7+IBIGN34Rgv+Rsgl1RNt8i9bBt7KJ4b5QVP kObHHMIWjacSwTjfHlphojvQG6ZoJtxmutK76LuVb5zNph2otTKjSu6e9v7dG85CX5qp /ZUeWSJZa6+15VCNA95293lQnjitxNStYywqEhGfprGR2cMKGHH5r/UDSXD2EdD+dK2Z XA6g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1686853612; x=1689445612; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=v5j0wCZPnfsM4/SjEwwVDfexZdOw0uK6iqseA0HQUzE=; b=CmwJ/APn7Zg8UiaEhr5Z9foFiW1Nhy6xzI1mNxKEVo/vRrUi3b0vvOONdk7VTMMaxc COpNPWAKuB2TJ1KBfFNIGoIegUKutbWIwmc/4HWn6JTp1Ex5toDbkQ+jPOA46bZJPiLW GHuWiQPXe+d/vGrDq7P5foFxJdtE+i5zoJ6HEflyrSwoztqSgBc3pOBGUxtpGVO3GqcX LPz1upKtEz6dFeCj1XktjW13KWvuBqaTrY0Rr8MWmwEw7+4j59i4dXE8TH23ZpfAGzya Tn6ZzSm5ib/OhzpO/yT4JMyiL4plT0KpebhsvjhtwAhlcuutK6Y3VEOLLl1nKhMQN5Vl orFg== X-Gm-Message-State: AC+VfDwNdr/KAblvLKSgoH24MeQLItPebZgTj9FEQGceTYaoYlY5Tq3U ZmVuuGLNdf5BHWMe1LmAP2HzrNw2Vck= X-Google-Smtp-Source: ACHHUZ4XblfvtELYfPfTXYv/mZguDzYqVYK+D/wTZAy9MdyrQSECLLlB+UmOM8NMKOmXv6Fwf6a/c1+W5jI= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a17:902:a70f:b0:1b5:64:1862 with SMTP id w15-20020a170902a70f00b001b500641862mr893196plq.9.1686853612603; Thu, 15 Jun 2023 11:26:52 -0700 (PDT) Date: Thu, 15 Jun 2023 11:26:51 -0700 In-Reply-To: <20230526234435.662652-10-yuzhao@google.com> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20230526234435.662652-1-yuzhao@google.com> <20230526234435.662652-10-yuzhao@google.com> Message-ID: Subject: Re: [PATCH mm-unstable v2 09/10] kvm/x86: add kvm_arch_test_clear_young() From: Sean Christopherson To: Yu Zhao Cc: Andrew Morton , Paolo Bonzini , Alistair Popple , Anup Patel , Ben Gardon , Borislav Petkov , Catalin Marinas , Chao Peng , Christophe Leroy , Dave Hansen , Fabiano Rosas , Gaosheng Cui , Gavin Shan , "H. Peter Anvin" , Ingo Molnar , James Morse , "Jason A. Donenfeld" , Jason Gunthorpe , Jonathan Corbet , Marc Zyngier , Masami Hiramatsu , Michael Ellerman , Michael Larabel , Mike Rapoport , Nicholas Piggin , Oliver Upton , Paul Mackerras , Peter Xu , Steven Rostedt , Suzuki K Poulose , Thomas Gleixner , Thomas Huth , Will Deacon , Zenghui Yu , kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-trace-kernel@vger.kernel.org, x86@kernel.org, linux-mm@google.com Content-Type: text/plain; charset="us-ascii" On Fri, May 26, 2023, Yu Zhao wrote: > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c > index 08340219c35a..6875a819e007 100644 > --- a/arch/x86/kvm/mmu/tdp_mmu.c > +++ b/arch/x86/kvm/mmu/tdp_mmu.c > @@ -1232,6 +1232,40 @@ bool kvm_tdp_mmu_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range) > return kvm_tdp_mmu_handle_gfn(kvm, range, test_age_gfn); > } > > +bool kvm_arch_test_clear_young(struct kvm *kvm, struct kvm_gfn_range *range) > +{ > + struct kvm_mmu_page *root; > + int offset = ffs(shadow_accessed_mask) - 1; > + > + if (kvm_shadow_root_allocated(kvm)) This needs a comment. > + return true; > + > + rcu_read_lock(); > + > + list_for_each_entry_rcu(root, &kvm->arch.tdp_mmu_roots, link) { As requested in v1[1], please add a macro for a lockless walk. [1] https://lkml.kernel.org/r/Y%2Fed0XYAPx%2B7pukA%40google.com > + struct tdp_iter iter; > + > + if (kvm_mmu_page_as_id(root) != range->slot->as_id) > + continue; > + > + tdp_root_for_each_leaf_pte(iter, root, range->start, range->end) { > + u64 *sptep = rcu_dereference(iter.sptep); > + > + VM_WARN_ON_ONCE(!page_count(virt_to_page(sptep))); Hrm, I don't like adding this in KVM. The primary MMU might guarantee that this callback is invoked if and only if the SPTE is backed by struct page memory, but there's no reason to assume that's true in KVM. If we want the sanity check, then this needs to use kvm_pfn_to_refcounted_page(). And it should use KVM's MMU_WARN_ON(), which is a mess and effectively dead code, but I'm working on changing that[*], i.e. by the time this gets to Linus' tree, the sanity check should have a much cleaner implementation. [2] https://lore.kernel.org/all/20230511235917.639770-8-seanjc@google.com > + > + if (!(iter.old_spte & shadow_accessed_mask)) > + continue; > + > + if (kvm_should_clear_young(range, iter.gfn)) > + clear_bit(offset, (unsigned long *)sptep); If/when you rebase on https://github.com/kvm-x86/linux/tree/next, can you pull out the atomic bits of tdp_mmu_clear_spte_bits() and use that new helper? E.g. diff --git a/arch/x86/kvm/mmu/tdp_iter.h b/arch/x86/kvm/mmu/tdp_iter.h index fae559559a80..914c34518829 100644 --- a/arch/x86/kvm/mmu/tdp_iter.h +++ b/arch/x86/kvm/mmu/tdp_iter.h @@ -58,15 +58,18 @@ static inline u64 kvm_tdp_mmu_write_spte(tdp_ptep_t sptep, u64 old_spte, return old_spte; } +static inline u64 tdp_mmu_clear_spte_bits_atomic(tdp_ptep_t sptep, u64 mask) +{ + atomic64_t *sptep_atomic = (atomic64_t *)rcu_dereference(sptep); + + return (u64)atomic64_fetch_and(~mask, sptep_atomic); +} + static inline u64 tdp_mmu_clear_spte_bits(tdp_ptep_t sptep, u64 old_spte, u64 mask, int level) { - atomic64_t *sptep_atomic; - - if (kvm_tdp_mmu_spte_need_atomic_write(old_spte, level)) { - sptep_atomic = (atomic64_t *)rcu_dereference(sptep); - return (u64)atomic64_fetch_and(~mask, sptep_atomic); - } + if (kvm_tdp_mmu_spte_need_atomic_write(old_spte, level)) + return tdp_mmu_clear_spte_bits_atomic(sptep, mask); __kvm_tdp_mmu_write_spte(sptep, old_spte & ~mask); return old_spte;