From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0A4C3ECAAD8 for ; Wed, 31 Aug 2022 03:18:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230511AbiHaDSU (ORCPT ); Tue, 30 Aug 2022 23:18:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55696 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229775AbiHaDSE (ORCPT ); Tue, 30 Aug 2022 23:18:04 -0400 Received: from out0-148.mail.aliyun.com (out0-148.mail.aliyun.com [140.205.0.148]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ED4EA4D245; Tue, 30 Aug 2022 20:18:02 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R171e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018047204;MF=houwenlong.hwl@antgroup.com;NM=1;PH=DS;RN=14;SR=0;TI=SMTPD_---.P3zI0Md_1661915879; Received: from localhost(mailfrom:houwenlong.hwl@antgroup.com fp:SMTPD_---.P3zI0Md_1661915879) by smtp.aliyun-inc.com; Wed, 31 Aug 2022 11:17:59 +0800 Date: Wed, 31 Aug 2022 11:17:59 +0800 From: "Hou Wenlong" To: Sean Christopherson Cc: kvm@vger.kernel.org, Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] KVM: x86: Return emulator error if RDMSR/WRMSR emulation failed Message-ID: <20220831031759.GA130753@k08j02272.eu95sqa> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 31, 2022 at 02:44:08AM +0800, Sean Christopherson wrote: > On Thu, Jul 28, 2022, Hou Wenlong wrote: > > The return value of emulator_{get|set}_mst_with_filter() > > is confused, since msr access error and emulator error > > are mixed. Although, KVM_MSR_RET_* doesn't conflict with > > X86EMUL_IO_NEEDED at present, it is better to convert > > msr access error to emulator error if error value is > > needed. > > > > Signed-off-by: Hou Wenlong > > --- > > arch/x86/kvm/x86.c | 22 ++++++++++++---------- > > 1 file changed, 12 insertions(+), 10 deletions(-) > > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > index 5366f884e9a7..8df89b9c212f 100644 > > --- a/arch/x86/kvm/x86.c > > +++ b/arch/x86/kvm/x86.c > > @@ -7908,11 +7908,12 @@ static int emulator_get_msr_with_filter(struct x86_emulate_ctxt *ctxt, > > int r; > > > > r = kvm_get_msr_with_filter(vcpu, msr_index, pdata); > > - > > - if (r && kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_RDMSR, 0, > > - complete_emulated_rdmsr, r)) { > > - /* Bounce to user space */ > > - return X86EMUL_IO_NEEDED; > > + if (r) { > > + if (kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_RDMSR, 0, > > + complete_emulated_rdmsr, r)) > > + r = X86EMUL_IO_NEEDED; > > + else > > + r = X86EMUL_UNHANDLEABLE; > > This should be X86EMUL_PROPAGATE_FAULT, X86EMUL_UNHANDLEABLE is used to indicate > that KVM needs to bail all the way to userspace. > > I definitely like the idea of converting to X86EMUL_* here instead of spreading > it across these helpers and the emulator, but in that case should convert _all_ > types. > > And I think it makes sense to opportunistically handle "r < 0" in the get helper. > KVM may not return -errno today, but assuming that will always hold true is > unnecessarily risking. I agree. The original commit 7dffecaf4eab wanted to report negative values to userspace, but the emulator actually didn't propagate -errno to the caller. So handling "r < 0" in the set helper is better, then only X86EMUL_* is returned. > > E.g. what about: > > > static int emulator_get_msr_with_filter(struct x86_emulate_ctxt *ctxt, > u32 msr_index, u64 *pdata) > { > struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt); > int r; > > r = kvm_get_msr_with_filter(vcpu, msr_index, pdata); > if (r < 0) > return X86EMUL_UNHANDLEABLE; > > if (r) { > if (kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_RDMSR, 0, > complete_emulated_rdmsr, r)) > return X86EMUL_IO_NEEDED; > else > return X86EMUL_PROPAGATE_FAULT; > } > > return X86EMUL_CONTINUE; > } > > static int emulator_set_msr_with_filter(struct x86_emulate_ctxt *ctxt, > u32 msr_index, u64 data) > { > struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt); > int r; > > r = kvm_set_msr_with_filter(vcpu, msr_index, data); > if (r < 0) > return X86EMUL_UNHANDLEABLE; > > if (r) { > if (kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_WRMSR, data, > complete_emulated_msr_access, r)) > return X86EMUL_IO_NEEDED; > else > return X86EMUL_PROPAGATE_FAULT; > } > > return X86EMUL_CONTINUE; > } > I'll take this in the v2. Thanks. > > Or maybe even add a helper to do the translation? Can't tell if this is a net > positive or not. It's a bit gratuitous, but it does ensure consistent behavior > for RDMSR vs. WRMSR. > > static int emulator_handle_msr_return(struct kvm_vcpu *vcpu *, int r, > u32 msr, u64 data, u32 exit_reason, > int (*comp)(struct kvm_vcpu *vcpu)) > { > if (r < 0) > return X86EMUL_UNHANDLEABLE; > > if (r) { > if (kvm_msr_user_space(vcpu, msr, exit_reason, data, comp, r)) > return X86EMUL_IO_NEEDED; > else > return X86EMUL_UNHANDLEABLE; > } > > return X86EMUL_CONTINUE; > } > > static int emulator_get_msr_with_filter(struct x86_emulate_ctxt *ctxt, > u32 msr_index, u64 *pdata) > { > struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt); > int r; > > r = kvm_get_msr_with_filter(vcpu, msr_index, pdata); > return emulator_handle_msr_return(vcpu, r, msr_index, 0, > KVM_EXIT_X86_RDMSR, > complete_emulated_rdmsr); > } > > static int emulator_set_msr_with_filter(struct x86_emulate_ctxt *ctxt, > u32 msr_index, u64 data) > { > struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt); > int r; > > r = kvm_set_msr_with_filter(vcpu, msr_index, data); > return emulator_handle_msr_return(vcpu, r, msr_index, data, > KVM_EXIT_X86_WRMSR, > complete_emulated_msr_access); > } > > > And then the emulator side of things can be: > > static int em_wrmsr(struct x86_emulate_ctxt *ctxt) > { > u64 msr_index = reg_read(ctxt, VCPU_REGS_RCX); > u64 msr_data; > int r; > > msr_data = (u32)reg_read(ctxt, VCPU_REGS_RAX) > | ((u64)reg_read(ctxt, VCPU_REGS_RDX) << 32); > r = ctxt->ops->set_msr_with_filter(ctxt, msr_index, msr_data); > > if (r == X86EMUL_PROPAGATE_FAULT) > return emulate_gp(ctxt, 0); > > return r; > } > > static int em_rdmsr(struct x86_emulate_ctxt *ctxt) > { > u64 msr_index = reg_read(ctxt, VCPU_REGS_RCX); > u64 msr_data; > int r; > > r = ctxt->ops->get_msr_with_filter(ctxt, msr_index, &msr_data); > > if (r == X86EMUL_PROPAGATE_FAULT) > return emulate_gp(ctxt, 0); > > if (r == X86EMUL_CONTINUE) { > *reg_write(ctxt, VCPU_REGS_RAX) = (u32)msr_data; > *reg_write(ctxt, VCPU_REGS_RDX) = msr_data >> 32; > } > return r; > }