From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 538F8EB64DB for ; Thu, 15 Jun 2023 18:26:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229730AbjFOS0z (ORCPT ); Thu, 15 Jun 2023 14:26:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38654 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229648AbjFOS0y (ORCPT ); Thu, 15 Jun 2023 14:26:54 -0400 Received: from mail-pl1-x64a.google.com (mail-pl1-x64a.google.com [IPv6:2607:f8b0:4864:20::64a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3301B1FD4 for ; Thu, 15 Jun 2023 11:26:53 -0700 (PDT) Received: by mail-pl1-x64a.google.com with SMTP id d9443c01a7336-1b516cb26c9so7792935ad.0 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=JHYGwo5oswm6+lFtg/cYykPpb7bnluTdHnfOTMH9iJ6U1Tq3pZrLoTjClnQ3C96jJU 616caZcCOy2rXGqgqd27slv3Yq+LA+pAD/PBwDZXohmtlYjFTLdUmkoep1uiKxeS39rB DbrxkiNdC4AkGkl4MuLM9JtsfbOk6BKpRoh4S4SiXZjeFHfTP2NK2Oy69jvs+CpT7ORu AzcA6heUf5fE3HW3ahAikOVRyQ3jhpkTT18vvXZWSRTENLlr+0IhSxwBjogP0F7PNMVw VtdjD4CfJj8/FMOdoJFtxAcr+FeTcH0XiVbX8SKmQEMuVhK2ju6H7sF06PHlFNqzgw8X 5z9w== X-Gm-Message-State: AC+VfDyKFyrWaSgNnxXyMLNcX0hQlrVy9jDb5WRWE2lnKPR7df/45A3o iGA7l6BSaLeTsABWhOyluxumUo/QLyI= 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> 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" Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org 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;