From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: kvm_regs vs kvm_sregs? Date: Sun, 18 Mar 2007 07:13:17 +0200 Message-ID: <45FCCA6D.3070207@qumranet.com> References: <1174057254.22955.13.camel@basalt> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: Hollis Blanchard Return-path: In-reply-to: <1174057254.22955.13.camel@basalt> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Hollis Blanchard wrote: > What is the distinction between kvm_regs and kvm_sregs? As far as I can > see, kvm_regs is only used when emulating IO, emulating MMIO, and > emulating CPUID, where guest GPRs are directly modified. kvm_sregs is > only used for full CPU state save (for later restore). > After the userspace interface changes, neither of them are used except for migration, savevm/loadvm, and debugging. Theoretically they could be unified, practically SET_SREGS is a dangerous operation on Intel cpus due to kvm's very imperfect real mode support. > When the kernel had to use copy_to_user() to transfer state to userland, > I can see that this split resulted in less memory copying. However, now > that userland can directly map register state without a copy, why not > combine the two structures? > We don't map the register state as that would require us to sync it on every exit. > I guess it takes longer to copy state out of the VMCS into kvm_sregs, so > why bother if userspace isn't going to use it? > When it's needed, it's really needed. Or did I misunderstand the question? -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV