From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCH v5 00/12] KVM: introduce readonly memslot Date: Fri, 10 Aug 2012 15:14:22 -0300 Message-ID: <20120810181422.GA14892@amt.cnet> References: <5020E423.9080004@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Avi Kivity , LKML , KVM To: Xiao Guangrong Return-path: Content-Disposition: inline In-Reply-To: <5020E423.9080004@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Tue, Aug 07, 2012 at 05:47:15PM +0800, Xiao Guangrong wrote: > Changelog: > - introduce KVM_PFN_ERR_RO_FAULT instead of dummy page > - introduce KVM_HVA_ERR_BAD and optimize error hva indicators > > The test case can be found at: > http://lkml.indiana.edu/hypermail/linux/kernel/1207.2/00819/migrate-perf.tar.bz2 > > In current code, if we map a readonly memory space from host to guest > and the page is not currently mapped in the host, we will get a fault-pfn > and async is not allowed, then the vm will crash. > > As Avi's suggestion, We introduce readonly memory region to map ROM/ROMD > to the guest, read access is happy for readonly memslot, write access on > readonly memslot will cause KVM_EXIT_MMIO exit. Memory slots whose QEMU mapping is write protected is supported today, as long as there are no write faults. What prevents the use of mmap(!MAP_WRITE) to handle read-only memslots again? The initial objective was to fix a vm crash, can you explain that initial problem?