From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH v3] KVM: x86 emulator: access GPRs on demand Date: Sun, 19 Aug 2012 12:32:36 +0300 Message-ID: <5030B2B4.8050100@redhat.com> References: <1345128889-29672-1-git-send-email-avi@redhat.com> <20120817172938.GA21708@amt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org To: Marcelo Tosatti Return-path: Received: from mx1.redhat.com ([209.132.183.28]:44730 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751358Ab2HSJcj (ORCPT ); Sun, 19 Aug 2012 05:32:39 -0400 Received: from int-mx01.intmail.prod.int.phx2.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q7J9WcYd007830 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Sun, 19 Aug 2012 05:32:38 -0400 In-Reply-To: <20120817172938.GA21708@amt.cnet> Sender: kvm-owner@vger.kernel.org List-ID: On 08/17/2012 08:29 PM, Marcelo Tosatti wrote: > On Thu, Aug 16, 2012 at 05:54:49PM +0300, Avi Kivity wrote: >> Instead of populating the the entire register file, read in registers >> as they are accessed, and write back only the modified ones. This >> saves a VMREAD and VMWRITE on Intel (for rsp, since it is not usually >> used during emulation), and a two 128-byte copies for the registers. >> > >> @@ -2715,14 +2764,17 @@ int emulator_task_switch(struct x86_emulate_ctxt *ctxt, >> { >> int rc; >> >> + invalidate_registers(ctxt); >> ctxt->_eip = ctxt->eip; >> ctxt->dst.type = OP_NONE; >> >> rc = emulator_do_task_switch(ctxt, tss_selector, idt_index, reason, >> has_error_code, error_code); >> >> - if (rc == X86EMUL_CONTINUE) >> + if (rc == X86EMUL_CONTINUE) { >> ctxt->eip = ctxt->_eip; >> + writeback_registers(ctxt); >> + } >> >> return (rc == X86EMUL_UNHANDLEABLE) ? EMULATION_FAILED : EMULATION_OK; >> } > > > No clear point when emulator register cache is active, when it is > not (AFAICS this patch does not invalidate registers on emulation start > (the above being one of the exceptions) does not clear valid bit on > writeback-to-vcpu-cache on emulation exit). It is cleared when emulation starts. For the non-insn-emulation entry points, there is an explicit invalidate. For the emulation entry point, there is a memset() that clears everything up to _regs, which includes the cache. This discrepancy isn't nice, but it preexists. I don't know whether we should decompose the memset() or not, it is rather efficient. > > Concern is that emulator can start with cached registers marked as valid > but in fact are invalid from previous emulation round. > > Maybe move invalidate() to init_emulate_ctxt? > See the memset() in init_decode_cache(). -- error compiling committee.c: too many arguments to function