From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xiao Guangrong Subject: Re: [PATCH] KVM: x86: fix missed memory synchronization when patch hypercall Date: Sun, 09 Jun 2013 17:08:34 +0800 Message-ID: <51B44612.6080704@gmail.com> References: <51B2A1D9.6060306@gmail.com> <20130609084526.GH4725@redhat.com> <51B4434A.2010402@gmail.com> <20130609085937.GJ4725@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Paolo Bonzini , Marcelo Tosatti , LKML , KVM To: Gleb Natapov Return-path: In-Reply-To: <20130609085937.GJ4725@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 06/09/2013 04:59 PM, Gleb Natapov wrote: > On Sun, Jun 09, 2013 at 04:56:42PM +0800, Xiao Guangrong wrote: >> On 06/09/2013 04:45 PM, Gleb Natapov wrote: >>> On Sat, Jun 08, 2013 at 11:15:37AM +0800, Xiao Guangrong wrote: >>>> From: Xiao Guangrong >>>> >>>> Currently, memory synchronization is missed in emulator_fix_hypercall, >>>> please see the commit 758ccc89b83 >>>> (KVM: x86: drop calling kvm_mmu_zap_all in emulator_fix_hypercall) >>>> >>>> This patch fixes it by introducing kvm_vcpus_hang_on_page_start() and >>>> kvm_vcpus_hang_on_page_end which unmap the patched page from guest >>>> and use kvm_flush_remote_tlbs() as the serializing instruction to >>>> ensure the memory coherence >>>> [ The SDM said that INVEPT, INVVPID and MOV (to control register, with >>>> the exception of MOV CR8) are the serializing instructions. ] >>>> >>>> The mmu-lock is held during host patches the page so that it stops vcpus >>>> to fix its further page fault >>>> >>> I have a patch to implement is much simple and in generic way, not >>> relying on MMU internals. >> >> I have considered this way but it seems not simple - it needs a new type of >> request and it forces all vcpus to hang when host is patching the page. >> >> My approach is just reusing the mmu code and requires vcpus to hang only when >> the patched page is bing accessed. > > That's very rare, no point to optimize this code path. Fine to me. I do not have strong opinion on that, please apply your patch instead. ;)