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Tue, 09 Mar 2021 11:36:06 +0000 Received: from mail.kernel.org ([198.145.29.99]) by desiato.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1lJaed-004L4Y-13 for linux-arm-kernel@lists.infradead.org; Tue, 09 Mar 2021 11:36:01 +0000 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 5BB9F651D1; Tue, 9 Mar 2021 11:35:57 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94) (envelope-from ) id 1lJaeZ-000WmM-Cq; Tue, 09 Mar 2021 11:35:55 +0000 Date: Tue, 09 Mar 2021 11:35:54 +0000 Message-ID: <87o8fsy2xx.wl-maz@kernel.org> From: Marc Zyngier To: Will Deacon Cc: kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, James Morse , Julien Thierry , Suzuki K Poulose , Alexandru Elisei , kernel-team@android.com Subject: Re: [PATCH] KVM: arm64: Cap default IPA size to the host's own size In-Reply-To: <20210309112658.GA28025@willie-the-truck> References: <20210308174643.761100-1-maz@kernel.org> <20210309112658.GA28025@willie-the-truck> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: will@kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, alexandru.elisei@arm.com, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210309_113559_762302_9994DF2F X-CRM114-Status: GOOD ( 30.18 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, 09 Mar 2021 11:26:59 +0000, Will Deacon wrote: > > On Mon, Mar 08, 2021 at 05:46:43PM +0000, Marc Zyngier wrote: > > KVM/arm64 has forever used a 40bit default IPA space, partially > > due to its 32bit heritage (where the only choice is 40bit). > > > > However, there are implementations in the wild that have a *cough* > > much smaller *cough* IPA space, which leads to a misprogramming of > > VTCR_EL2, and a guest that is stuck on its first memory access > > if userspace dares to ask for the default IPA setting (which most > > VMMs do). > > > > Instead, cap the default IPA size to what the host can actually > > do, and spit out a one-off message on the console. The boot warning > > is turned into a more meaningfull message, and the new behaviour > > is also documented. > > > > Although this is a userspace ABI change, it doesn't really change > > much for userspace: > > > > - the guest couldn't run before this change, while it now has > > a chance to if the memory range fits the reduced IPA space > > > > - a memory slot that was accepted because it did fit the default > > IPA space but didn't fit the HW constraints is now properly > > rejected > > > > The other thing that's left doing is to convince userspace to > > actually use the IPA space setting instead of relying on the > > antiquated default. > > Is there a way for userspace to discover the default IPA size, or does > it have to try setting values until it finds one that sticks? Yes, since 233a7cb23531 ("kvm: arm64: Allow tuning the physical address size for VM"). The VMM can issue a KVM_CAP_ARM_VM_IPA_SIZE ioctl(), and get in return the maximum IPA size (I have a patch for kvmtool that does this). M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel