From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Maydell Subject: Re: [PATCH 4/4] arm/arm64: KVM: use kernel mapping to perform invalidation on page fault Date: Thu, 8 Jan 2015 15:21:50 +0000 Message-ID: References: <1420718349-24152-1-git-send-email-marc.zyngier@arm.com> <1420718349-24152-5-git-send-email-marc.zyngier@arm.com> <54AE811F.4020104@arm.com> <54AE9D0F.3060002@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: Christoffer Dall , kvm-devel , "kvmarm@lists.cs.columbia.edu" To: Marc Zyngier Return-path: Received: from mail-lb0-f176.google.com ([209.85.217.176]:51912 "EHLO mail-lb0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756696AbbAHPWM (ORCPT ); Thu, 8 Jan 2015 10:22:12 -0500 Received: by mail-lb0-f176.google.com with SMTP id p9so3414491lbv.7 for ; Thu, 08 Jan 2015 07:22:10 -0800 (PST) In-Reply-To: <54AE9D0F.3060002@arm.com> Sender: kvm-owner@vger.kernel.org List-ID: On 8 January 2015 at 15:06, Marc Zyngier wrote: > On 08/01/15 13:16, Peter Maydell wrote: >>> ASID cached VIVT icaches are also VMID tagged. It is thus impossible for >>> stale cache lines to come with a new page. And if by synchronizing the >>> caches you obtain a different instruction stream, it means you've >>> restored the wrong page. >> >> ...is that true even if the dirty data in the dcache comes from >> the userspace process doing DMA or writing the initial boot >> image or whatever? > > We perform this on a page that is being brought in stage-2. Two cases: > > - This is a page is mapped for the first time: the icache should be > invalid for this page (the guest should have invalidated it the first > place), If this is the first instruction in the guest (ie we've just (warm) reset the VM and are running the kernel as loaded into the guest by QEMU/kvmtool) then the guest can't have invalidated the icache, and QEMU can't do the invalidate because it doesn't have the vaddr and VMID of the guest. > - This is a page that we bring back from swap: the page must match the > one that has been swapped out. If it has been DMA'ed in in the meantime, > then the guest surely has flushed its icache if it intends to branch to > it, hasn't it? I agree that for the DMA case the guest will have done the invalidate. -- PMM