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 204CECA100C for ; Tue, 5 Sep 2023 21:09:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238246AbjIEVJv (ORCPT ); Tue, 5 Sep 2023 17:09:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60070 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234306AbjIEVJu (ORCPT ); Tue, 5 Sep 2023 17:09:50 -0400 Received: from mail-pf1-x44a.google.com (mail-pf1-x44a.google.com [IPv6:2607:f8b0:4864:20::44a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8CD8A1BB for ; Tue, 5 Sep 2023 14:09:40 -0700 (PDT) Received: by mail-pf1-x44a.google.com with SMTP id d2e1a72fcca58-68bec4380edso312365b3a.1 for ; Tue, 05 Sep 2023 14:09:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1693948180; x=1694552980; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=HxWd/JxgmSGajFF87A8h9wNUEFwW+sZa+eEy3CYAxpg=; b=Gc5STmxqUeIoxFwRhte5YyhM4UOJ5MIgSmqvewy6bq2GHf7MbfmQMHhHuuXHmX+AvO IW1K7oK+6n+uqRMwrhC678PeMiBvoab0nbvMazhOYnhl3iXPZQhGIn+sak//iT+M5kDe sCZxtDn2SFFlmvEbSfeQp2I+VmXKz7kzdWgJUcaU5O+kyXiWylSIS/D9VS12PJ/7QxH9 tXx3czKZK9VbYLc4LKgwOUUr1Hst52QypGDtfsEqbJduj7+a0mMOnApjZQhKBbw6V3Ai aAjHcRo4oO//Gp/4GFTsK9v/J6MofD8garwT7G0Lb3HNR7T4LB9WkzdP4uyA058xJZof NdKA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1693948180; x=1694552980; 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=HxWd/JxgmSGajFF87A8h9wNUEFwW+sZa+eEy3CYAxpg=; b=B8eGZfUPGxjnycue5hWd2WR+NV95B8+fOsP4aWcYt9SmOIMRzUmwoVm90nzez3/3IW OO00NHB3c3kLrO6eYG8EYUIB64bPiUZ8A+tHAk2Q9DF0Z3OcGT/x+ewnE2zBWgVulNxL BzbbhbxU/Ay47S0u9FSn8UQJuKb7f8cOcM8fIGVrAv1z6oyq9BwFV0EuHkd/ccVSHgqV OIO8QQqqI0pEVRFJI9JkMQLQdmp+95adYKGvcbFM6yPeX1/K8HJ/5eoRqEd+iX4xEDkZ LtiF7XWBD1QvinDNUD/Ys+wjWQRBjVGckD4JkSe4qjft1oz7hDzR2bQBJaGYtSvU4zSq rVdQ== X-Gm-Message-State: AOJu0YzQQberxs88+CEDUJXZpl36/f2iqgEivsjUBE5DoQkFPDm6aTlq nJVaH1/hFR4fA0iqW4twlPP8F2rGM4w= X-Google-Smtp-Source: AGHT+IGI+Vz9BgR1PXF97IznQmBHRaIcD4F8AI2rGPVPalycx2vl24NpJSXelSsFzyRf0WUSSrif3BRxw+k= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:6a00:2d0d:b0:68a:5937:ea87 with SMTP id fa13-20020a056a002d0d00b0068a5937ea87mr5398834pfb.3.1693948179970; Tue, 05 Sep 2023 14:09:39 -0700 (PDT) Date: Tue, 5 Sep 2023 14:09:38 -0700 In-Reply-To: <99cf9b5929418e8876e95a169d20ee26e126c51c.camel@intel.com> Mime-Version: 1.0 References: <20230902175431.2925-1-zeming@nfschina.com> <99cf9b5929418e8876e95a169d20ee26e126c51c.camel@intel.com> Message-ID: Subject: Re: [PATCH] x86/kvm/mmu: =?utf-8?Q?Remove_?= =?utf-8?B?dW5uZWNlc3Nhcnkg4oCYTlVMTOKAmQ==?= values from sptep From: Sean Christopherson To: Kai Huang Cc: "zeming@nfschina.com" , "x86@kernel.org" , "dave.hansen@linux.intel.com" , "bp@alien8.de" , "mingo@redhat.com" , "tglx@linutronix.de" , "kvm@vger.kernel.org" , "pbonzini@redhat.com" , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset="us-ascii" Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Sep 04, 2023, Kai Huang wrote: > On Fri, 2023-09-01 at 09:48 -0700, Sean Christopherson wrote: > > @@ -3447,6 +3447,14 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault) > > else > > sptep = fast_pf_get_last_sptep(vcpu, fault->addr, &spte); > > > > + /* > > + * It's entirely possible for the mapping to have been zapped > > + * by a different task, but the root page is should always be > > + * available as the vCPU holds a reference to its root(s). > > + */ > > + if (WARN_ON_ONCE(!sptep)) > > + spte = REMOVED_SPTE; > > If I recall correctly, REMOVED_SPTE is only used by TDP MMU code. Should we use > 0 (or initial SPTE value for case like TDX) instead of REMOVED_SPTE? I deliberately suggested REMOVED_SPTE in part because of TDX introducing "initial SPTE"; finding/remembering '0' initialization of SPTEs is hard. Though FWIW, '0' would be totally fine for TDX because the value is never exposed to hardware. I think it's totally fine to use REMOVED_SPTE like this in common code, I would be quite surprised if it causes confusion. Even though REMOVED_SPTE was introduced by the TDP MMU, its value/semantics are generic.