From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yw1-f202.google.com (mail-yw1-f202.google.com [209.85.128.202]) (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 01EA17B for ; Wed, 15 Feb 2023 17:07:46 +0000 (UTC) Received: by mail-yw1-f202.google.com with SMTP id 00721157ae682-50e79ffba49so221594957b3.9 for ; Wed, 15 Feb 2023 09:07:46 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=I40PJrFRqn61VwCmmZvurXKna/KGPzaaS+rQHZXZvn0=; b=l8u1qpGgi11tT4E8pv9pTuFXHM/7WY2MCiv2bszlJ1zxeExjqm25IM6hph3zf0n+GH ysvNzeo91bE0dHqERdOSLN9nkAhwpdM8rvp4LDTHjt0IYdwmbCUNot0/sh9QF2e0g+4Z iXxjc61Os8fGMeChQfy7xU38ALBiYCz8AYDCwTG4waTH3d1iDkVZc0yYh5UNBmH9BNIC 4s4k2LCWdlix0TbeFAYqhetPtDE28k4vgwnqcFslAgOyUWGhqcYIEmTs3P2wcstRRrmQ ULTCsPbzrtYJpit4Rb6KoytvdVRvTJo64CyT87HR+oXbZKIrYwa+Kqzs6Ne5vw5YvgZQ r+vg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; 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=I40PJrFRqn61VwCmmZvurXKna/KGPzaaS+rQHZXZvn0=; b=XA+EqMVVH6omC95XRmbZBxzR0qCRyalKT64VE1gL6JQ39wCMm3qJsthyyHwhu5zS1R U3frxTBSkx4w5DRThWpe1pRmXq32vbxF5k++JOcVnA00LdDUk7Eb3qVv0ckiY1ws2qrV 6mpSd9EHzdx8gALGvaXoFK2ks7rwM5489Wym0+P1Mg9+oL+NVG/IZHFV/ELnYkB0pUWQ 4ZT9JXp+zQaO/7MhRH3nLn4fyHxeJsiUeJu2JqdYmfOWC+XzMjYFRW4ecWhk0LJGDVQT rM3MlQ3V3ORgGZ/1Srlt85qbuJ3rbTlseY7PEQVPxuOwjKNx8XhDEBt/G8XVQzmlnW4h V+WQ== X-Gm-Message-State: AO0yUKUiliQiHe452pNFnMRXfjRRIvSn7+94jMw9MbMZ1ljj49SzfQX7 c7ShAk5qEJUBxtjcmxGtPJx1c/ory1E= X-Google-Smtp-Source: AK7set/bKyGjjQSPDfHloXqvYliTaSoAw87YpPgzxpVLEYaD/uIjcgxZV0daIcoU5fiuPAjFav357tj93Iw= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:6902:2c2:b0:920:2b79:84b4 with SMTP id w2-20020a05690202c200b009202b7984b4mr349239ybh.386.1676480865897; Wed, 15 Feb 2023 09:07:45 -0800 (PST) Date: Wed, 15 Feb 2023 09:07:44 -0800 In-Reply-To: <87mt5fz5g6.wl-maz@kernel.org> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20230215011614.725983-1-amoorthy@google.com> <20230215011614.725983-6-amoorthy@google.com> <87mt5fz5g6.wl-maz@kernel.org> Message-ID: Subject: Re: [PATCH 5/8] kvm: Add cap/kvm_run field for memory fault exits From: Sean Christopherson To: Marc Zyngier Cc: Anish Moorthy , Paolo Bonzini , Oliver Upton , James Houghton , Ben Gardon , David Matlack , Ricardo Koller , Chao Peng , Axel Rasmussen , kvm@vger.kernel.org, kvmarm@lists.linux.dev Content-Type: text/plain; charset="us-ascii" On Wed, Feb 15, 2023, Marc Zyngier wrote: > On Wed, 15 Feb 2023 01:16:11 +0000, Anish Moorthy wrote: > > 8. Other capabilities. > > ====================== > > > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > > index 109b18e2789c4..9352e7f8480fb 100644 > > --- a/include/linux/kvm_host.h > > +++ b/include/linux/kvm_host.h > > @@ -801,6 +801,9 @@ struct kvm { > > bool vm_bugged; > > bool vm_dead; > > > > + rwlock_t mem_fault_nowait_lock; > > + bool mem_fault_nowait; > > A full-fat rwlock to protect a single bool? What benefits do you > expect from a rwlock? Why is it preferable to an atomic access, or a > simple bitop? There's no need to have any kind off dedicated atomicity. The only readers are in vCPU context, just disallow KVM_CAP_MEM_FAULT_NOWAIT after vCPUs are created.