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 X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2580AC433DF for ; Sat, 23 May 2020 07:59:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F350D206C3 for ; Sat, 23 May 2020 07:59:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alien8.de header.i=@alien8.de header.b="ZLEXWPqM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387756AbgEWH7c (ORCPT ); Sat, 23 May 2020 03:59:32 -0400 Received: from mail.skyhub.de ([5.9.137.197]:57804 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387627AbgEWH7b (ORCPT ); Sat, 23 May 2020 03:59:31 -0400 Received: from zn.tnic (p200300ec2f1b96004c59f332ede330a0.dip0.t-ipconnect.de [IPv6:2003:ec:2f1b:9600:4c59:f332:ede3:30a0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 215841EC0338; Sat, 23 May 2020 09:59:30 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1590220770; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=PIo+t2JcI6yVRedmlgz10X421O+M066c0hltaVL112k=; b=ZLEXWPqMrm4G0DwJpbs8Xgi9xF4kgV5KjgjmvT9VK9gOBCLZtVjao6/GkCbl6+4X+V5fwU RC9EWJFZV06I1nR899eptspZxrdViE5apbzfahsF0PgTl3LX1V8HCCJUtgslfPsCUj9YUS /PGarM2WPPCDvyJoyVnqQyWd5w4+ROU= Date: Sat, 23 May 2020 09:59:24 +0200 From: Borislav Petkov To: Joerg Roedel Cc: x86@kernel.org, hpa@zytor.com, Andy Lutomirski , Dave Hansen , Peter Zijlstra , Thomas Hellstrom , Jiri Slaby , Dan Williams , Tom Lendacky , Juergen Gross , Kees Cook , David Rientjes , Cfir Cohen , Erdem Aktas , Masami Hiramatsu , Mike Stunes , Joerg Roedel , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCH v3 47/75] x86/sev-es: Add Runtime #VC Exception Handler Message-ID: <20200523075924.GB27431@zn.tnic> References: <20200428151725.31091-1-joro@8bytes.org> <20200428151725.31091-48-joro@8bytes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200428151725.31091-48-joro@8bytes.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 28, 2020 at 05:16:57PM +0200, Joerg Roedel wrote: > diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c > index a4fa7f351bf2..bc3a58427028 100644 > --- a/arch/x86/kernel/sev-es.c > +++ b/arch/x86/kernel/sev-es.c > @@ -10,6 +10,7 @@ > #include /* For show_regs() */ > #include > #include > +#include > #include > #include > #include > @@ -25,7 +26,7 @@ > #include > #include > #include > -#include > +#include > #include > > /* For early boot hypervisor communication in SEV-ES enabled guests */ > @@ -46,10 +47,26 @@ struct sev_es_runtime_data { > > /* Physical storage for the per-cpu IST stacks of the #VC handler */ > struct vmm_exception_stacks vc_stacks __aligned(PAGE_SIZE); > + > + /* Reserve on page per CPU as backup storage for the unencrypted GHCB */ one > + struct ghcb backup_ghcb; I could use some text explaining what those backups are for? > + /* > + * Mark the per-cpu GHCBs as in-use to detect nested #VC exceptions. > + * There is no need for it to be atomic, because nothing is written to > + * the GHCB between the read and the write of ghcb_active. So it is safe > + * to use it when a nested #VC exception happens before the write. > + */ Looks liks that is that text... support for nested #VC exceptions. I'm sure this has come up already but why do we even want to support nested #VCs? IOW, can we do without them first or are they absolutely necessary? I'm guessing VC exceptions inside the VC handler but what are the sensible use cases? Thx. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette