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From: Oliver Upton To: Ricardo Koller Subject: Re: [PATCH 2/4] KVM: arm64: Don't serialize if the access flag isn't set Message-ID: References: <20221129191946.1735662-1-oliver.upton@linux.dev> <20221129191946.1735662-3-oliver.upton@linux.dev> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT Cc: kvm@vger.kernel.org, Marc Zyngier , linux-kernel@vger.kernel.org, Catalin Marinas , kvmarm@lists.linux.dev, Will Deacon , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu Hi Ricardo, Thanks for having a look. On Tue, Nov 29, 2022 at 12:52:12PM -0800, Ricardo Koller wrote: > On Tue, Nov 29, 2022 at 07:19:44PM +0000, Oliver Upton wrote: [...] > > + ret = stage2_update_leaf_attrs(pgt, addr, 1, KVM_PTE_LEAF_ATTR_LO_S2_AF, 0, > > + &pte, NULL, 0); > > + if (!ret) > > + dsb(ishst); > > At the moment, the only reason for stage2_update_leaf_attrs() to not > update the PTE is if it's not valid: > > if (!kvm_pte_valid(pte)) > return 0; > > I guess you could check that as well: > > + if (!ret || kvm_pte_valid(pte)) > + dsb(ishst); Thanks for catching this. Instead of pivoting on the returned PTE value, how about we return -EAGAIN from the early return in stage2_attr_walker()? It would better match the pattern used elsewhere in the pgtable code. -- Thanks, Oliver _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out2.migadu.com (out2.migadu.com [188.165.223.204]) (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 8A2B0BA28 for ; Tue, 29 Nov 2022 21:15:27 +0000 (UTC) Date: Tue, 29 Nov 2022 21:15:21 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1669756525; 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=FtYFpXu5/fa0TaYiI4P0+GO9iWhqJmCXUsHphTqwjGw=; b=oE86JcLcGxsicJ5+/muPqhDr7FrTiNs6WD8LcTD34Qo6fvG4ULczduWra99AnJWXD8Xtg0 garTf7J0LX7RmBFNAhjKicG/NVDNgHM7JNlVsJIgPMT0ZyHg3SMpR3SR8h5DHbZkmS+wfD UYYEx/SftPydGa+lK+iguxXp2/OPh14= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Oliver Upton To: Ricardo Koller Cc: Marc Zyngier , James Morse , Alexandru Elisei , Suzuki K Poulose , Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/4] KVM: arm64: Don't serialize if the access flag isn't set Message-ID: References: <20221129191946.1735662-1-oliver.upton@linux.dev> <20221129191946.1735662-3-oliver.upton@linux.dev> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev 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 Message-ID: <20221129211521.domT0FWh7AhJfCbpFTU1LEQLuHF4vt9mfGMymwdqihE@z> Hi Ricardo, Thanks for having a look. On Tue, Nov 29, 2022 at 12:52:12PM -0800, Ricardo Koller wrote: > On Tue, Nov 29, 2022 at 07:19:44PM +0000, Oliver Upton wrote: [...] > > + ret = stage2_update_leaf_attrs(pgt, addr, 1, KVM_PTE_LEAF_ATTR_LO_S2_AF, 0, > > + &pte, NULL, 0); > > + if (!ret) > > + dsb(ishst); > > At the moment, the only reason for stage2_update_leaf_attrs() to not > update the PTE is if it's not valid: > > if (!kvm_pte_valid(pte)) > return 0; > > I guess you could check that as well: > > + if (!ret || kvm_pte_valid(pte)) > + dsb(ishst); Thanks for catching this. Instead of pivoting on the returned PTE value, how about we return -EAGAIN from the early return in stage2_attr_walker()? It would better match the pattern used elsewhere in the pgtable code. -- Thanks, Oliver