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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 B8821C43334 for ; Thu, 6 Sep 2018 13:50:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 73BA220844 for ; Thu, 6 Sep 2018 13:50:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 73BA220844 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730058AbeIFS0V (ORCPT ); Thu, 6 Sep 2018 14:26:21 -0400 Received: from mga03.intel.com ([134.134.136.65]:46434 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726926AbeIFS0V (ORCPT ); Thu, 6 Sep 2018 14:26:21 -0400 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 06 Sep 2018 06:50:41 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.53,338,1531810800"; d="scan'208";a="86534589" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.20]) by fmsmga004.fm.intel.com with ESMTP; 06 Sep 2018 06:50:41 -0700 Date: Thu, 6 Sep 2018 06:50:41 -0700 From: Sean Christopherson To: Borislav Petkov Cc: Brijesh Singh , x86@kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Tom Lendacky , Thomas Gleixner , "H. Peter Anvin" , Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= Subject: Re: [PATCH v5 5/5] x86/kvm: Avoid dynamic allocation of pvclock data when SEV is active Message-ID: <20180906135041.GB32336@linux.intel.com> References: <1536234182-2809-1-git-send-email-brijesh.singh@amd.com> <1536234182-2809-6-git-send-email-brijesh.singh@amd.com> <20180906122423.GA11144@zn.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180906122423.GA11144@zn.tnic> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 06, 2018 at 02:24:23PM +0200, Borislav Petkov wrote: > On Thu, Sep 06, 2018 at 06:43:02AM -0500, Brijesh Singh wrote: > > Currently, the per-cpu pvclock data is allocated dynamically when > > cpu > HVC_BOOT_ARRAY_SIZE. The physical address of this variable is > > shared between the guest and the hypervisor hence it must be mapped as > > unencrypted (ie. C=0) when SEV is active. > > > > When SEV is active, we will be wasting fairly sizeable amount of memory > > since each CPU will be doing a separate 4k allocation so that it can clear > > C-bit. Let's define few extra static page sized array of pvclock data. > > In the preparatory stage of CPU hotplug, use the element of this static > > array to avoid the dynamic allocation. This array will be put in > > the .data..decrypted section so that its mapped with C=0 during the boot. > > > > In non-SEV case, this static page will unused and free'd by the > > free_decrypted_mem(). > > > > Signed-off-by: Brijesh Singh > > Suggested-by: Sean Christopherson > > Cc: Tom Lendacky > > Cc: kvm@vger.kernel.org > > Cc: Thomas Gleixner > > Cc: Borislav Petkov > > Cc: "H. Peter Anvin" > > Cc: linux-kernel@vger.kernel.org > > Cc: Paolo Bonzini > > Cc: Sean Christopherson > > Cc: kvm@vger.kernel.org > > Cc: "Radim Krčmář" > > --- > > arch/x86/include/asm/mem_encrypt.h | 4 ++++ > > arch/x86/kernel/kvmclock.c | 22 +++++++++++++++++++--- > > arch/x86/kernel/vmlinux.lds.S | 3 +++ > > arch/x86/mm/init.c | 3 +++ > > arch/x86/mm/mem_encrypt.c | 10 ++++++++++ > > 5 files changed, 39 insertions(+), 3 deletions(-) > > > > diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h > > index 802b2eb..aa204af 100644 > > --- a/arch/x86/include/asm/mem_encrypt.h > > +++ b/arch/x86/include/asm/mem_encrypt.h > > @@ -48,11 +48,13 @@ int __init early_set_memory_encrypted(unsigned long vaddr, unsigned long size); > > > > /* Architecture __weak replacement functions */ > > void __init mem_encrypt_init(void); > > +void __init free_decrypted_mem(void); > > > > bool sme_active(void); > > bool sev_active(void); > > > > #define __decrypted __attribute__((__section__(".data..decrypted"))) > > +#define __decrypted_hvclock __attribute__((__section__(".data..decrypted_hvclock"))) > > So are we going to be defining a decrypted section for every piece of > machinery now? > > That's a bit too much in my book. > > Why can't you simply free everything in .data..decrypted on !SVE guests? That would prevent adding __decrypted to existing declarations, e.g. hv_clock_boot, which would be ugly in its own right. A more generic solution would be to add something like __decrypted_exclusive to mark data that is used if and only if SEV is active, and then free the SEV-only data when SEV is disabled. Originally, my thought was that this would be a one-off case and the array could be freed directly in kvmclock_init(), e.g.: static struct pvclock_vsyscall_time_info hv_clock_aux[HVC_AUX_ARRAY_SIZE] __decrypted __aligned(PAGE_SIZE); ... void __init kvmclock_init(void) { u8 flags; if (!sev_active()) free_init_pages("unused decrypted", (unsigned long)hv_clock_aux, (unsigned long)hv_clock_aux + sizeof(hv_clock_aux)); > > -- > Regards/Gruss, > Boris. > > SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) > --