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 B00ABEB64DA for ; Wed, 28 Jun 2023 22:57:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231645AbjF1W5S (ORCPT ); Wed, 28 Jun 2023 18:57:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54542 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230326AbjF1W5O (ORCPT ); Wed, 28 Jun 2023 18:57:14 -0400 Received: from mail-yw1-x1149.google.com (mail-yw1-x1149.google.com [IPv6:2607:f8b0:4864:20::1149]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4B72226B9 for ; Wed, 28 Jun 2023 15:57:12 -0700 (PDT) Received: by mail-yw1-x1149.google.com with SMTP id 00721157ae682-565ba5667d5so538557b3.0 for ; Wed, 28 Jun 2023 15:57:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1687993031; x=1690585031; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=hwgSA/+Q3RwZ/y/YZJGoooMBAh627PahKu/KzBnos0s=; b=Oskss3t+pC064I6YCeM23QPiq/UnvLj6LANVC7YxVDbWHJUnifSzqz29R96QnU+IdF wye1IcGLqykZvDZMmi8yOmpioxKLnKtiOrvp6LAw3PWIisM/3TMlr5OwTXiuq74MV7lF HZKIpqx/pjlhrjmmFTC2IsMbMD73e1rrEvyFi1KX996EXXw8/ci2mFWs9UKERmrvNeba 79KN777V5kWTkiHBKFKzDMLFwwKsKt+ldSLBrgKrBL/C+xL6BeRFk9iU1LRTtMRhN/A7 GBXSgjol6OyCKtuQaO2VyklYLzCuWI2VipFHkvD+LANt04oUTKjv3eQHmRVJwlB1ufrL efeQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1687993031; x=1690585031; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=hwgSA/+Q3RwZ/y/YZJGoooMBAh627PahKu/KzBnos0s=; b=ecYwHmoLFiOyKtw3UlBs9di+X2X99A518i0RLK/pMlq6ah7fcDNAj73w71d2iWkEQ6 ThSjiZAhNtEkJeYx/qY0poyoTrivTO5y4hqk7pkvk3tCglqbzr6zleycJFm0fEK1/Uvv gKUVZ6VMR433aLQ5f3D4j+Gr0xmnWlDG2TfT56uKGkrVa7ihFBJsszTwIRMjKzMYv/mf h+Pce9FzAwGS0ZQ9bCXaHILs2AbpV9Z2X1y8E++VWv7WC7XF8u+Ixw8ibiZSr1+47nIC wOO660Crpz8b2QsFN0Mud8u9Q61vA4Fr47RZKKsuj5meqi2NxqTMttzzPjvaEkfKGwTb /wJw== X-Gm-Message-State: AC+VfDwHIgO04innhjF3LKIll82X9Z7vLvL0D2jRlXB6zaQkgCIBat8I l1d9q45cQahhWjFw7UvciBDDQyfuha0= X-Google-Smtp-Source: ACHHUZ7zCOG9RSK63m/viGHrTVnLManN+Bek2z4NKfPkzS1lEk61765VeWfKqH5jp32gijPhHUu9Ay6Hn6U= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a81:b1c5:0:b0:570:b1:ca37 with SMTP id p188-20020a81b1c5000000b0057000b1ca37mr14108433ywh.5.1687993031424; Wed, 28 Jun 2023 15:57:11 -0700 (PDT) Date: Wed, 28 Jun 2023 15:57:09 -0700 In-Reply-To: <20230616023858.7503-1-yan.y.zhao@intel.com> Mime-Version: 1.0 References: <20230616023101.7019-1-yan.y.zhao@intel.com> <20230616023858.7503-1-yan.y.zhao@intel.com> Message-ID: Subject: Re: [PATCH v3 08/11] KVM: x86: move vmx code to get EPT memtype when CR0.CD=1 to x86 common code From: Sean Christopherson To: Yan Zhao Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, chao.gao@intel.com, kai.huang@intel.com, robert.hoo.linux@gmail.com Content-Type: text/plain; charset="us-ascii" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 16, 2023, Yan Zhao wrote: > Move code in vmx.c to get cache disabled memtype when non-coherent DMA > present to x86 common code. > > This is the preparation patch for later implementation of fine-grained gfn > zap for CR0.CD toggles when guest MTRRs are honored. > > No functional change intended. > > Signed-off-by: Yan Zhao > --- > arch/x86/kvm/mtrr.c | 19 +++++++++++++++++++ > arch/x86/kvm/vmx/vmx.c | 10 +++++----- > arch/x86/kvm/x86.h | 1 + > 3 files changed, 25 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c > index 3ce58734ad22..b35dd0bc9cad 100644 > --- a/arch/x86/kvm/mtrr.c > +++ b/arch/x86/kvm/mtrr.c > @@ -721,3 +721,22 @@ bool kvm_mtrr_check_gfn_range_consistency(struct kvm_vcpu *vcpu, gfn_t gfn, > > return type == mtrr_default_type(mtrr_state); > } > + > +void kvm_mtrr_get_cd_memory_type(struct kvm_vcpu *vcpu, u8 *type, bool *ipat) Hmm, I'm not convinced that this logic is subtle enough to warrant a common helper with out params (I *really* don't like out params :-) ). UC, or more specifically CR0.CD=1 on VMX without the quirk, is a super special case, because to faithfully emulatee "No Fill" mode, KVM needs to ignore guest PAT (stupid WC). I don't love having the same logic/assumptions in multiple places, but the CR0.CD=1 behavior is so rigidly tied to what KVM must do to that I think trying to provide a common helper makes the code more complex than it needs to be. If we open code the logic in the MTRR helper, than I think it can be distilled down to: struct kvm_mtrr *mtrr_state = &vcpu->arch.mtrr_state; bool mtrr_enabled = mtrr_is_enabled(mtrr_state); u8 default_type; /* * Faithfully emulating CR0.CD=1 on VMX requires ignoring guest PAT, as * WC in the PAT overrides UC in the MTRRs. Zap all SPTEs so that KVM * will once again start honoring guest PAT. */ if (!kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_CD_NW_CLEARED)) return kvm_mtrr_zap_gfn_range(vcpu, gpa_to_gfn(0), gpa_to_gfn(~0ULL)); default_type = mtrr_enabled ? mtrr_default_type(mtrr_state) : mtrr_disabled_type(vcpu); if (default_type != MTRR_TYPE_WRBACK) return kvm_mtrr_zap_gfn_range(vcpu, gpa_to_gfn(0), gpa_to_gfn(~0ULL)); if (mtrr_enabled) { if (gather_non_wb_fixed_mtrrs(vcpu, MTRR_TYPE_WRBACK)) goto fail; if (gather_non_wb_var_mtrrs(vcpu, MTRR_TYPE_WRBACK)) goto fail; kvm_zap_or_wait_mtrrs(vcpu->kvm); } and this patch goes away. > +{ > + /* > + * this routine is supposed to be called when guest mtrrs are honored > + */ > + if (unlikely(!kvm_mmu_honors_guest_mtrrs(vcpu->kvm))) { I don't think this is worth checking, e.g. this would be WARN-worthy if it weren't for an otherwise benign race with device (un)assignment. > + *type = MTRR_TYPE_WRBACK; > + *ipat = true; > + } else if (unlikely(!kvm_check_has_quirk(vcpu->kvm, Eh, drop the "unlikely()" annotations. AIUI, they almost never provide actual performance benefits, and I dislike unnecessarily speculating on what userspace is doing when it comes to code (though I 100% agree that this definitely unlikely)