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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 0DE76C433E0 for ; Fri, 29 May 2020 14:34:34 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id DB0452073B for ; Fri, 29 May 2020 14:34:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DB0452073B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jeg5X-0008In-0c; Fri, 29 May 2020 14:34:23 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jeg5V-0008Ie-TA for xen-devel@lists.xenproject.org; Fri, 29 May 2020 14:34:21 +0000 X-Inumbo-ID: 7bad2dbc-a1b9-11ea-a8c9-12813bfff9fa Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 7bad2dbc-a1b9-11ea-a8c9-12813bfff9fa; Fri, 29 May 2020 14:34:20 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id AAE7DB001; Fri, 29 May 2020 14:34:19 +0000 (UTC) Subject: Re: [PATCH] x86/svm: do not try to handle recalc NPT faults immediately To: Igor Druzhinin References: <1590712553-7298-1-git-send-email-igor.druzhinin@citrix.com> From: Jan Beulich Message-ID: Date: Fri, 29 May 2020 16:34:19 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <1590712553-7298-1-git-send-email-igor.druzhinin@citrix.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: xen-devel@lists.xenproject.org, roger.pau@citrix.com, george.dunlap@citrix.com, wl@xen.org, andrew.cooper3@citrix.com Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 29.05.2020 02:35, Igor Druzhinin wrote: > A recalculation NPT fault doesn't always require additional handling > in hvm_hap_nested_page_fault(), moreover in general case if there is no > explicit handling done there - the fault is wrongly considered fatal. > > Instead of trying to be opportunistic - use safer approach and handle > P2M recalculation in a separate NPT fault by attempting to retry after > making the necessary adjustments. This is aligned with Intel behavior > where there are separate VMEXITs for recalculation and EPT violations > (faults) and only faults are handled in hvm_hap_nested_page_fault(). > Do it by also unifying do_recalc return code with Intel implementation > where returning 1 means P2M was actually changed. > > This covers a specific case of migration with vGPU assigned on AMD: > global log-dirty is enabled and causes immediate recalculation NPT > fault in MMIO area upon access. To be honest, from this last paragraph I still can't really derive what goes wrong exactly why, before this change. > Signed-off-by: Igor Druzhinin > --- > This is a safer alternative to: > https://lists.xenproject.org/archives/html/xen-devel/2020-05/msg01662.html > and more correct approach from my PoV. Indeed - I was about to reply there, but then I thought I'd first look at this patch, in case it was a replacement. > --- a/xen/arch/x86/hvm/svm/svm.c > +++ b/xen/arch/x86/hvm/svm/svm.c > @@ -2923,9 +2923,10 @@ void svm_vmexit_handler(struct cpu_user_regs *regs) > v->arch.hvm.svm.cached_insn_len = vmcb->guest_ins_len & 0xf; > rc = vmcb->exitinfo1 & PFEC_page_present > ? p2m_pt_handle_deferred_changes(vmcb->exitinfo2) : 0; > - if ( rc >= 0 ) > + if ( rc == 0 ) > + /* If no recal adjustments were being made - handle this fault */ > svm_do_nested_pgfault(v, regs, vmcb->exitinfo1, vmcb->exitinfo2); > - else > + else if ( rc < 0 ) So from going through the code and judging by the comment in finish_type_change() (which btw you will need to update, to avoid it becoming stale) the >= here was there just in case, without there actually being any case where a positive value would be returned. It that's also the conclusion you've drawn, then I think it would help mentioning this in the description. It is also desirable to mention finish_type_change() not being affected, as already dealing with the > 0 case. > --- a/xen/arch/x86/mm/p2m-pt.c > +++ b/xen/arch/x86/mm/p2m-pt.c > @@ -340,7 +340,7 @@ static int do_recalc(struct p2m_domain *p2m, unsigned long gfn) > unsigned long gfn_remainder = gfn; > unsigned int level = 4; > l1_pgentry_t *pent; > - int err = 0; > + int err = 0, rc = 0; > > table = map_domain_page(pagetable_get_mfn(p2m_get_pagetable(p2m))); > while ( --level ) > @@ -402,6 +402,8 @@ static int do_recalc(struct p2m_domain *p2m, unsigned long gfn) > clear_recalc(l1, e); > err = p2m->write_p2m_entry(p2m, gfn, pent, e, level + 1); > ASSERT(!err); > + > + rc = 1; > } > } > unmap_domain_page((void *)((unsigned long)pent & PAGE_MASK)); > @@ -448,12 +450,14 @@ static int do_recalc(struct p2m_domain *p2m, unsigned long gfn) > clear_recalc(l1, e); > err = p2m->write_p2m_entry(p2m, gfn, pent, e, level + 1); > ASSERT(!err); > + > + rc = 1; > } > > out: > unmap_domain_page(table); > > - return err; > + return err ? err : rc; Typically we write this as "err ?: rc". I'd like to ask that "rc" also be renamed, to something like "recalc_done", and then to become bool. Jan