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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 40071C27C75 for ; Tue, 11 Jun 2024 16:52:59 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id CE6EA6B009E; Tue, 11 Jun 2024 12:52:58 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C97376B009F; Tue, 11 Jun 2024 12:52:58 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B852B6B00A0; Tue, 11 Jun 2024 12:52:58 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 9AF8E6B009E for ; Tue, 11 Jun 2024 12:52:58 -0400 (EDT) Received: from smtpin15.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 1B6D0A13D3 for ; Tue, 11 Jun 2024 16:52:58 +0000 (UTC) X-FDA: 82219202436.15.6B01A3B Received: from mail-qt1-f173.google.com (mail-qt1-f173.google.com [209.85.160.173]) by imf05.hostedemail.com (Postfix) with ESMTP id 5135B10000B for ; Tue, 11 Jun 2024 16:52:56 +0000 (UTC) Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=google.com header.s=20230601 header.b=V2ZoPiWU; spf=pass (imf05.hostedemail.com: domain of jthoughton@google.com designates 209.85.160.173 as permitted sender) smtp.mailfrom=jthoughton@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1718124776; a=rsa-sha256; cv=none; b=y6WCzdgp2++dWcxmFDhE/CErXTyJ/JJ4NwrNFZst6fzp3X74Q6NS3l+E0jjWKCshqy1RqO sKaTHackcummrElYZnToxG+ixsSnF+innrTVvigdmtylZ2wrPvuaMuU9qtOE0aiOPsS12v yoF7EdaNRgwnF6q+WrVSptXhIdaA9S4= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=google.com header.s=20230601 header.b=V2ZoPiWU; spf=pass (imf05.hostedemail.com: domain of jthoughton@google.com designates 209.85.160.173 as permitted sender) smtp.mailfrom=jthoughton@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1718124776; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=dNrvkbjbmCuGBxHxb5OVsA/4jQBqGMp/CsGTWofpaJ8=; b=F2CJOHSV5dUrm1zmbzhzlbfWNbLAlLcibbBpqkkEVtlidIF8YRROyqJLdw1/rbR5TablaR /iIjdiaJYUmHxmgEfII1kCfFMnjQTGdUx6JR3UihK4SiD5EfeTPFHCNrma2e0xmtIMYi9E 2MyrreDh2jzmYPZSbnP8agddbpJ9kPg= Received: by mail-qt1-f173.google.com with SMTP id d75a77b69052e-44056f72257so141cf.0 for ; Tue, 11 Jun 2024 09:52:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1718124775; x=1718729575; darn=kvack.org; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=dNrvkbjbmCuGBxHxb5OVsA/4jQBqGMp/CsGTWofpaJ8=; b=V2ZoPiWUVwfUT6H9Db+2n6JctsNn5EMHdbOFUDhMWrsX40FLIaBf7K3PCRNE6bqTVW +02o8Xk751ZZu0H9Um7ZFAvbbeZdbhzlNFwVxDoXsMJ53SLJAskFdng22uYs27JYC/q/ 4GM2apBM5UVIsyoA+Nj6dXKljS6AToljapRsRkk4LHJu2akQzR7dZ+qovEva+mehNQ2q PBNSWfERBYzfLQVx3lcgMQ6LXdaOFpR3Oaa5tetBGweMXL6UcM2znIUoru7m/Tzv/ydT kivqlZ21p4wtE3xpOjduoL+ZgNDMKgAEQ8oT7yV5monBFKXgf+wXrVehmH4r6l9CKftH VYIw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1718124775; x=1718729575; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=dNrvkbjbmCuGBxHxb5OVsA/4jQBqGMp/CsGTWofpaJ8=; b=sYaYICgirFCwIyLmkcLYXySGIJ9q5uwci643LpSLPhgBJ9AGN9bBAZy92kOQPgB5lh MxLYNDoIzEXUwNLVMoMfDJ7bXkxIv49VoJ28Rlsyh76Dc6oJrSA8kL0GjFvWjgmodL+H 6ZdNSnNuoT1y+rLILLCN9ZeIOtYEGY0RTTxRfe/TxNRhGnfBGF6JOZx5WPCie/fxzzxe 1y0gEQxUzyozZ59KGiQt6v4dfooZ1vsAA1rIjtAu+y0GA1y3k51BzRLRpWh6u4PtF5VI 8t62n7JpcjohRZuki5SI2efyScVW6U2rFiNvyuwVEt/lS1cBYoPKTFsi0Hn/r78TgRyt B0pw== X-Forwarded-Encrypted: i=1; AJvYcCUfDS5JlUdm1NMXy1ujpHhML1xV7l50m3naXsGi/PI6Wb911+j0jc6MOFHQ1VsWjwFububY8ULVWXiRHO80gESZv1I= X-Gm-Message-State: AOJu0YwgIItPLDbsl5YlDViTinqjGS46fmDQQprSGDTi8sxaf5IuVX9e QiIZwT92JmtD5y2rDRVVNTcYCA7Pjyi3x2mEBz0HPUQ+EIiDT7xpUJY+CEoetlDZ3kcrutYJHIk p14onQIn7LB+D+CaYoJBJTQIdKSxoUj2wj8z6 X-Google-Smtp-Source: AGHT+IETSJr/vthLSu4M/9Ufm7UR5Sik6z7Xo2T1/mUMxnuXtcmtqz9kCiAXEk/F0m7s9fStq+7fFskXaiSQE2MAAyQ= X-Received: by 2002:a05:622a:550d:b0:441:3c01:d0fa with SMTP id d75a77b69052e-4414798d3c1mr3642241cf.23.1718124775151; Tue, 11 Jun 2024 09:52:55 -0700 (PDT) MIME-Version: 1.0 References: <20240611002145.2078921-1-jthoughton@google.com> <20240611002145.2078921-4-jthoughton@google.com> In-Reply-To: From: James Houghton Date: Tue, 11 Jun 2024 09:52:17 -0700 Message-ID: Subject: Re: [PATCH v5 3/9] KVM: arm64: Relax locking for kvm_test_age_gfn and kvm_age_gfn To: Oliver Upton Cc: Andrew Morton , Paolo Bonzini , Ankit Agrawal , Axel Rasmussen , Catalin Marinas , David Matlack , David Rientjes , James Morse , Jonathan Corbet , Marc Zyngier , Raghavendra Rao Ananta , Ryan Roberts , Sean Christopherson , Shaoqin Huang , Suzuki K Poulose , Wei Xu , Will Deacon , Yu Zhao , 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: qcwt6x5n4gdufqniezicksbyzynm8hsr X-Rspamd-Queue-Id: 5135B10000B X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1718124776-721263 X-HE-Meta: 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 rOW8WvLU e+cDCYf4SwTQI0x5Ll4UR52uYrpoGC72ay/5aR/jOQEy7MgxMz/6BmUJWTAsmCM5cG7UJnDdxse09RJiV8RzhuV9Q22X+bDfoBt2CozSlmFY/z4RxCXoHO2ArlHMwBMX4Kh6FnD0/ocbgtSr/xbb9pWI7q629W3VcZLd0BypkF7oK2PPnVB/csJlQCWfinRiZCT2RAwxj7N9RNA8= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jun 10, 2024 at 10:58=E2=80=AFPM Oliver Upton wrote: > > On Tue, Jun 11, 2024 at 12:21:39AM +0000, James Houghton wrote: > > Replace the MMU write locks (taken in the memslot iteration loop) for > > read locks. > > > > Grabbing the read lock instead of the write lock is safe because the > > only requirement we have is that the stage-2 page tables do not get > > deallocated while we are walking them. The stage2_age_walker() callback > > is safe to race with itself; update the comment to reflect the > > synchronization change. > > > > Signed-off-by: James Houghton > > --- > > arch/arm64/kvm/Kconfig | 1 + > > arch/arm64/kvm/hyp/pgtable.c | 15 +++++++++------ > > arch/arm64/kvm/mmu.c | 26 ++++++++++++++++++++------ > > 3 files changed, 30 insertions(+), 12 deletions(-) > > > > diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig > > index 58f09370d17e..7a1af8141c0e 100644 > > --- a/arch/arm64/kvm/Kconfig > > +++ b/arch/arm64/kvm/Kconfig > > @@ -22,6 +22,7 @@ menuconfig KVM > > select KVM_COMMON > > select KVM_GENERIC_HARDWARE_ENABLING > > select KVM_GENERIC_MMU_NOTIFIER > > + select KVM_MMU_NOTIFIER_YOUNG_LOCKLESS > > select HAVE_KVM_CPU_RELAX_INTERCEPT > > select KVM_MMIO > > select KVM_GENERIC_DIRTYLOG_READ_PROTECT > > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.= c > > index 9e2bbee77491..b1b0f7148cff 100644 > > --- a/arch/arm64/kvm/hyp/pgtable.c > > +++ b/arch/arm64/kvm/hyp/pgtable.c > > @@ -1319,10 +1319,10 @@ static int stage2_age_walker(const struct kvm_p= gtable_visit_ctx *ctx, > > data->young =3D true; > > > > /* > > - * stage2_age_walker() is always called while holding the MMU loc= k for > > - * write, so this will always succeed. Nonetheless, this delibera= tely > > - * follows the race detection pattern of the other stage-2 walker= s in > > - * case the locking mechanics of the MMU notifiers is ever change= d. > > + * This walk may not be exclusive; the PTE is permitted to change > > s/may not/is not/ Will fix. > > > + * from under us. If there is a race to update this PTE, then the > > + * GFN is most likely young, so failing to clear the AF is likely > > + * to be inconsequential. > > */ > > if (data->mkold && !stage2_try_set_pte(ctx, new)) > > return -EAGAIN; > > @@ -1345,10 +1345,13 @@ bool kvm_pgtable_stage2_test_clear_young(struct= kvm_pgtable *pgt, u64 addr, > > struct kvm_pgtable_walker walker =3D { > > .cb =3D stage2_age_walker, > > .arg =3D &data, > > - .flags =3D KVM_PGTABLE_WALK_LEAF, > > + .flags =3D KVM_PGTABLE_WALK_LEAF | > > + KVM_PGTABLE_WALK_SHARED, > > }; > > + int r; > > > > - WARN_ON(kvm_pgtable_walk(pgt, addr, size, &walker)); > > + r =3D kvm_pgtable_walk(pgt, addr, size, &walker); > > + WARN_ON(r && r !=3D -EAGAIN); > > I could've been more explicit last time around, could you please tone > this down to WARN_ON_ONCE() as well? Will do, thanks. > > > return data.young; > > } > > > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > > index 8bcab0cc3fe9..a62c27a347ed 100644 > > --- a/arch/arm64/kvm/mmu.c > > +++ b/arch/arm64/kvm/mmu.c > > @@ -1773,25 +1773,39 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struc= t kvm_gfn_range *range) > > bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range) > > { > > u64 size =3D (range->end - range->start) << PAGE_SHIFT; > > + bool young =3D false; > > + > > + read_lock(&kvm->mmu_lock); > > > > if (!kvm->arch.mmu.pgt) > > return false; > > I'm guessing you meant to have 'goto out' here, since this early return > fails to drop the mmu_lock. Ah sorry! Thanks for catching this.