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 0AD47E7AD76 for ; Tue, 3 Oct 2023 16:07:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240285AbjJCQHS (ORCPT ); Tue, 3 Oct 2023 12:07:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42552 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239239AbjJCQHQ (ORCPT ); Tue, 3 Oct 2023 12:07:16 -0400 Received: from mgamail.intel.com (mgamail.intel.com [134.134.136.100]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3409FAB; Tue, 3 Oct 2023 09:07:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1696349233; x=1727885233; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=wymdIEl8VVVgMijc78DcYYzoGVblxaV2STsFsGMfpf0=; b=WD70Xu6mpjkvjxwRuh3sdyOcRYLY0dCZ/UxXUP2mkil5cmMDy1D3aKL4 2JRkvCGeeAdRqWvj6CvXL4stU9w/XGUir7wXAggW/mUhCo/IQupyoxMj2 Y6dyWPHgWsUT8ZeREieu6TgHr8FXvYvqxwPd603kVFOkJ6PeXc4gLPPWo 873iI3OC+587oDMZactzBPnEyE5iW8yBcIiM9pdQbT9E75kyMx/e5n9pv WIReMUpLcHSiJtuCm4MxYE4bC3vdcGJvTvlOt+JtW44xubDgEHgdBFf9I bnp+HYMFKjLuDi3xhaZs5/cqSH7vtJb4J+WcHvtH1gdrfJeekDFiflLKm Q==; X-IronPort-AV: E=McAfee;i="6600,9927,10852"; a="449406312" X-IronPort-AV: E=Sophos;i="6.03,197,1694761200"; d="scan'208";a="449406312" Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Oct 2023 09:07:07 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10852"; a="700760945" X-IronPort-AV: E=Sophos;i="6.03,197,1694761200"; d="scan'208";a="700760945" Received: from ddiaz-mobl4.amr.corp.intel.com (HELO [10.209.57.36]) ([10.209.57.36]) by orsmga003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Oct 2023 09:07:07 -0700 Message-ID: Date: Tue, 3 Oct 2023 09:07:06 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Subject: Re: [PATCH] arch/x86: Set XSS while handling #VC intercept for CPUID Content-Language: en-US To: Jinank Jain , seanjc@google.com, pbonzini@redhat.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, jinankjain@microsoft.com, thomas.lendacky@amd.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: wei.liu@kernel.org, tiala@microsoft.com References: <20231003092835.18974-1-jinankjain@linux.microsoft.com> From: Dave Hansen In-Reply-To: <20231003092835.18974-1-jinankjain@linux.microsoft.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/3/23 02:28, Jinank Jain wrote: ... > diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c > index 2eabccde94fb..92350a24848c 100644 > --- a/arch/x86/kernel/sev-shared.c > +++ b/arch/x86/kernel/sev-shared.c > @@ -880,6 +880,9 @@ static enum es_result vc_handle_cpuid(struct ghcb *ghcb, > if (snp_cpuid_ret != -EOPNOTSUPP) > return ES_VMM_ERROR; > > + if (regs->ax == 0xD && regs->cx == 0x1) > + ghcb_set_xss(ghcb, 0); The spec talks about leaf 0xD, but not the subleaf: > XSS is only required to besupplied when a request forCPUID 0000_000D > is made andthe guest supports the XSS MSR(0x0000_0DA0). Why restrict this to subleaf (regx->cx) 1? Second, XCR0 is being supplied regardless of the CPUID leaf. Why should XSS be restricted to 0xD while XCR0 is universally supplied? Third, why is it OK to supply a garbage (0) value? If the GHCB field is required it's surely because the host *NEEDS* the value to do something. Won't a garbage value potentially confuse the host?