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Mon, 27 Apr 2020 17:49:49 +0100 MIME-Version: 1.0 Date: Mon, 27 Apr 2020 17:49:49 +0100 From: Marc Zyngier To: =?UTF-8?Q?Andr=C3=A9_Przywara?= Subject: Re: [PATCH][kvmtool] kvm: Request VM specific limits instead of system-wide ones In-Reply-To: References: <20200427141738.285217-1-maz@kernel.org> Message-ID: <3886cae6b5e7e1fc9ab821f1d734036f@kernel.org> X-Sender: maz@kernel.org User-Agent: Roundcube Webmail/1.3.10 X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: andre.przywara@arm.com, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, will@kernel.org, ardb@kernel.org, Alexandru.Elisei@arm.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Cc: kvm@vger.kernel.org, Ard Biesheuvel , Will Deacon , kvmarm@lists.cs.columbia.edu 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-Transfer-Encoding: base64 Content-Type: text/plain; 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Mon, 27 Apr 2020 16:49:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588006191; bh=jQ0KWWZhLYMByhegFoIiVPOZdGk0Lzl4q7rMMcBmaew=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=mOIirCPKrFvI4awGm7xtERC/1d+1IFdK9FBuJhvAwXVySQ6LtQOVV3941dL88nHln oPon4b0PTqtO0zEbbez/LxcvR5zQJZEss/YQkxoUjDL4VVdWlJ5sHqC5/9CyDhSBvL AY2QX+K9rJ4UMv2Vu2x1pstXgUgGx3aJduDVdEj8= Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1jT6x3-006mzt-Ds; Mon, 27 Apr 2020 17:49:49 +0100 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Date: Mon, 27 Apr 2020 17:49:49 +0100 From: Marc Zyngier To: =?UTF-8?Q?Andr=C3=A9_Przywara?= Cc: kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, James Morse , Julien Thierry , Suzuki K Poulose , Will Deacon , Ard Biesheuvel , Alexandru Elisei Subject: Re: [PATCH][kvmtool] kvm: Request VM specific limits instead of system-wide ones In-Reply-To: References: <20200427141738.285217-1-maz@kernel.org> Message-ID: <3886cae6b5e7e1fc9ab821f1d734036f@kernel.org> X-Sender: maz@kernel.org User-Agent: Roundcube Webmail/1.3.10 X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: andre.przywara@arm.com, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, will@kernel.org, ardb@kernel.org, Alexandru.Elisei@arm.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 2020-04-27 16:37, André Przywara wrote: > On 27/04/2020 15:17, Marc Zyngier wrote: > Hi, > >> On arm64, the maximum number of vcpus is constrained by the type >> of interrupt controller that has been selected (GICv2 imposes a >> limit of 8 vcpus, while GICv3 currently has a limit of 512). >> >> It is thus important to request this limit on the VM file descriptor >> rather than on the one that corresponds to /dev/kvm, as the latter >> is likely to return something that doesn't take the constraints into >> account. > > That sounds reasonable, but I fail to find any distinction in the > kernel > code. We don't make any difference between the VM or the system FD in > the ioctl handler for those two extensions. For arm64 we always return > max. 512 (max VCPUs on GICv3), and number of online host cores for the > recommended value. For arm there was a distinction between GICv3 > support > compiled in or not, but otherwise the same constant values returned. > Quickly tested on Juno and N1SDP, the ioctls return the same expected > values, regardless of sys_fd vs vm_fd. > > So what am I missing here? Is this for some older or even newer > kernels? You're missing this: https://lore.kernel.org/kvm/20200427141507.284985-1-maz@kernel.org/ which adds the missing bits to the kernel. Thanks, M. -- Jazz is not dead. It just smells funny...