From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexander Graf Subject: Re: [PATCHv3] kvmppc: Implement H_LOGICAL_CI_{LOAD,STORE} in KVM Date: Tue, 17 Mar 2015 02:44:00 -0400 Message-ID: <5507CD30.4060501@suse.de> References: <1423097605-2169-1-git-send-email-david@gibson.dropbear.id.au> <54D2BFE7.9070204@suse.de> <20150317014113.GL5741@voom.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: paulus@samba.org, aik@ozlabs.ru, kvm-ppc@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: David Gibson Return-path: In-Reply-To: <20150317014113.GL5741@voom.redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 16.03.15 21:41, David Gibson wrote: > On Thu, Feb 05, 2015 at 01:57:11AM +0100, Alexander Graf wrote: >> >> >> On 05.02.15 01:53, David Gibson wrote: >>> On POWER, storage caching is usually configured via the MMU - attributes >>> such as cache-inhibited are stored in the TLB and the hashed page table. >>> >>> This makes correctly performing cache inhibited IO accesses awkward when >>> the MMU is turned off (real mode). Some CPU models provide special >>> registers to control the cache attributes of real mode load and stores but >>> this is not at all consistent. This is a problem in particular for SLOF, >>> the firmware used on KVM guests, which runs entirely in real mode, but >>> which needs to do IO to load the kernel. >>> >>> To simplify this qemu implements two special hypercalls, H_LOGICAL_CI_LOAD >>> and H_LOGICAL_CI_STORE which simulate a cache-inhibited load or store to >>> a logical address (aka guest physical address). SLOF uses these for IO. >>> >>> However, because these are implemented within qemu, not the host kernel, >>> these bypass any IO devices emulated within KVM itself. The simplest way >>> to see this problem is to attempt to boot a KVM guest from a virtio-blk >>> device with iothread / dataplane enabled. The iothread code relies on an >>> in kernel implementation of the virtio queue notification, which is not >>> triggered by the IO hcalls, and so the guest will stall in SLOF unable to >>> load the guest OS. >>> >>> This patch addresses this by providing in-kernel implementations of the >>> 2 hypercalls, which correctly scan the KVM IO bus. Any access to an >>> address not handled by the KVM IO bus will cause a VM exit, hitting the >>> qemu implementation as before. >>> >>> Note that a userspace change is also required, in order to enable these >>> new hcall implementations with KVM_CAP_PPC_ENABLE_HCALL. >>> >>> Signed-off-by: David Gibson >> >> Thanks, applied to kvm-ppc-queue. > > Any news on when this might go up to mainline? I'm aiming for 4.1. Alex