From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-173.mta0.migadu.com (out-173.mta0.migadu.com [91.218.175.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8FCA669DF7 for ; Fri, 31 May 2024 19:18:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717183106; cv=none; b=pBnA/SObIfeihc2/MUxyvlIabdjGHKgvzzKbyHq60d207gjowkIXmgtRqhSY1t7Odl2gi8bJOrYyOlXbShZ8GVXbATnO1/5ARKNSlWom2I5df93KgXLw5f+VCnKalFvylA5NYcHzPUmF7jEmxJHEQY9s6SexnyH2UiK7N/QlwE4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717183106; c=relaxed/simple; bh=8HZ1n1s6qKTPU9KH0f7lccCKB3kfMQ8uzpkLiQlx0XM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=bg2O3geoKyXg0oHk2u2z7Z6tZ3nVN3w2yyvlMC82VAcBQSmGc+POM3g8yf1MdtuT/Lubqxk0mr6Q8Ngd8+6xU14v1bENbY9nMS7oPCEsivPl3NVUi7Av21/qzOiTArrZD/FBBbvTDfxlzQPeLp8s46NxzLPJxl3xfOiMnKTYR6o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=OL//CPF3; arc=none smtp.client-ip=91.218.175.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="OL//CPF3" X-Envelope-To: jthoughton@google.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1717183102; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=2PNxbejm0F++LAZR/c3kykM2MBahftMSuulGipIjRRI=; b=OL//CPF3OaxDLNyUcF7L7kyNMf3VPjTvzSryLUW5C3BaNJ8N7qvdo+GYUTIaqfYoH8qbo6 hUFuWYcFNlSydh5QitAFxaO+uiSO8irmL6Dy7FoK51VSXO1IpH+zzZd24unXmg4kvPBA2e eDLUrnlpHUL5vYjUk6kginvv7JlKt2g= X-Envelope-To: akpm@linux-foundation.org X-Envelope-To: pbonzini@redhat.com X-Envelope-To: aou@eecs.berkeley.edu X-Envelope-To: ankita@nvidia.com X-Envelope-To: anup@brainfault.org X-Envelope-To: atishp@atishpatra.org X-Envelope-To: axelrasmussen@google.com X-Envelope-To: maobibo@loongson.cn X-Envelope-To: catalin.marinas@arm.com X-Envelope-To: dmatlack@google.com X-Envelope-To: rientjes@google.com X-Envelope-To: chenhuacai@kernel.org X-Envelope-To: james.morse@arm.com X-Envelope-To: corbet@lwn.net X-Envelope-To: maz@kernel.org X-Envelope-To: mpe@ellerman.id.au X-Envelope-To: npiggin@gmail.com X-Envelope-To: palmer@dabbelt.com X-Envelope-To: paul.walmsley@sifive.com X-Envelope-To: rananta@google.com X-Envelope-To: ryan.roberts@arm.com X-Envelope-To: seanjc@google.com X-Envelope-To: shahuang@redhat.com X-Envelope-To: shuah@kernel.org X-Envelope-To: suzuki.poulose@arm.com X-Envelope-To: zhaotianrui@loongson.cn X-Envelope-To: will@kernel.org X-Envelope-To: yuzhao@google.com X-Envelope-To: yuzenghui@huawei.com X-Envelope-To: kvm-riscv@lists.infradead.org X-Envelope-To: kvm@vger.kernel.org X-Envelope-To: kvmarm@lists.linux.dev X-Envelope-To: linux-arm-kernel@lists.infradead.org X-Envelope-To: linux-doc@vger.kernel.org X-Envelope-To: linux-kernel@vger.kernel.org X-Envelope-To: linux-kselftest@vger.kernel.org X-Envelope-To: linux-mips@vger.kernel.org X-Envelope-To: linux-mm@kvack.org X-Envelope-To: linux-riscv@lists.infradead.org X-Envelope-To: linuxppc-dev@lists.ozlabs.org X-Envelope-To: loongarch@lists.linux.dev Date: Fri, 31 May 2024 12:18:11 -0700 X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Oliver Upton To: James Houghton Cc: Andrew Morton , Paolo Bonzini , Albert Ou , Ankit Agrawal , Anup Patel , Atish Patra , Axel Rasmussen , Bibo Mao , Catalin Marinas , David Matlack , David Rientjes , Huacai Chen , James Morse , Jonathan Corbet , Marc Zyngier , Michael Ellerman , Nicholas Piggin , Palmer Dabbelt , Paul Walmsley , Raghavendra Rao Ananta , Ryan Roberts , Sean Christopherson , Shaoqin Huang , Shuah Khan , Suzuki K Poulose , Tianrui Zhao , Will Deacon , Yu Zhao , Zenghui Yu , kvm-riscv@lists.infradead.org, kvm@vger.kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, loongarch@lists.linux.dev Subject: Re: [PATCH v4 6/7] KVM: arm64: Relax locking for kvm_test_age_gfn and kvm_age_gfn Message-ID: References: <20240529180510.2295118-1-jthoughton@google.com> <20240529180510.2295118-7-jthoughton@google.com> Precedence: bulk X-Mailing-List: linux-mips@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT On Fri, May 31, 2024 at 12:11:33PM -0700, Oliver Upton wrote: > On Wed, May 29, 2024 at 06:05:09PM +0000, James Houghton wrote: > > [...] > > > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > > index 9e2bbee77491..eabb07c66a07 100644 > > --- a/arch/arm64/kvm/hyp/pgtable.c > > +++ b/arch/arm64/kvm/hyp/pgtable.c > > @@ -1319,10 +1319,8 @@ static int stage2_age_walker(const struct kvm_pgtable_visit_ctx *ctx, > > data->young = true; > > > > /* > > - * stage2_age_walker() is always called while holding the MMU lock for > > - * write, so this will always succeed. Nonetheless, this deliberately > > - * follows the race detection pattern of the other stage-2 walkers in > > - * case the locking mechanics of the MMU notifiers is ever changed. > > + * This walk may not be exclusive; the PTE is permitted to change > > + * from under us. > > */ > > if (data->mkold && !stage2_try_set_pte(ctx, new)) > > return -EAGAIN; > > It is probably worth mentioning that if there was a race to update the > PTE then the GFN is most likely young, so failing to clear AF probably > isn't even consequential. Oh, and the WARN_ON() in kvm_pgtable_stage2_test_clear_young() is bogus now. Maybe demote it to: r = kvm_pgtable_walk(...); WARN_ON_ONCE(r && r != -EAGAIN); -- Thanks, Oliver