From patchwork Fri Jul 31 12:39:25 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Paul Durrant X-Patchwork-Id: 11694881 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 76D2E912 for ; Fri, 31 Jul 2020 12:40:13 +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 526F721744 for ; Fri, 31 Jul 2020 12:40:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=xen.org header.i=@xen.org header.b="QgyL/2yv" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 526F721744 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=xen.org 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 1k1UJy-0007T5-1L; Fri, 31 Jul 2020 12:39:34 +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 1k1UJw-0007SZ-4K for xen-devel@lists.xenproject.org; Fri, 31 Jul 2020 12:39:32 +0000 X-Inumbo-ID: e13c6308-d32a-11ea-abab-12813bfff9fa Received: from mail.xenproject.org (unknown [104.130.215.37]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id e13c6308-d32a-11ea-abab-12813bfff9fa; Fri, 31 Jul 2020 12:39:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xen.org; s=20200302mail; h=Content-Transfer-Encoding:Content-Type:MIME-Version: References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From:Sender:Reply-To: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=z2IY39FopPNWgEDc6LGpyAvx8fgxPmSJFUs3X+CwziI=; b=QgyL/2yvdHMIT/RvS5+x0seXrH jkEXLIHDeIgKtoc0gHI/Lx4mj+nsTsK3PZw4CkHP6Ih56vM5Q/RL6YROl6omiQfgGa6Dsein+2gEa 9JtcTfIFllo6Xi0HJO8qh74OYSyMsN6aEqoiN1ISiyULsP0eN8bL2O1atcQePU9E0HHY=; Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1k1UJu-0001A8-Gz; Fri, 31 Jul 2020 12:39:30 +0000 Received: from host86-143-223-30.range86-143.btcentralplus.com ([86.143.223.30] helo=u2f063a87eabd5f.home) by xenbits.xenproject.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1k1UJu-0007EP-9l; Fri, 31 Jul 2020 12:39:30 +0000 From: Paul Durrant To: xen-devel@lists.xenproject.org Subject: [PATCH v2 1/2] x86/hvm: set 'ipat' in EPT for special pages Date: Fri, 31 Jul 2020 13:39:25 +0100 Message-Id: <20200731123926.28970-2-paul@xen.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200731123926.28970-1-paul@xen.org> References: <20200731123926.28970-1-paul@xen.org> MIME-Version: 1.0 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: Andrew Cooper , Paul Durrant , Wei Liu , Jan Beulich , =?utf-8?q?Roger_Pau_Monn=C3=A9?= Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" From: Paul Durrant All non-MMIO ranges (i.e those not mapping real device MMIO regions) that map valid MFNs are normally marked MTRR_TYPE_WRBACK and 'ipat' is set. Hence when PV drivers running in a guest populate the BAR space of the Xen Platform PCI Device with pages such as the Shared Info page or Grant Table pages, accesses to these pages will be cachable. However, should IOMMU mappings be enabled be enabled for the guest then these accesses become uncachable. This has a substantial negative effect on I/O throughput of PV devices. Arguably PV drivers should bot be using BAR space to host the Shared Info and Grant Table pages but it is currently commonplace for them to do this and so this problem needs mitigation. Hence this patch makes sure the 'ipat' bit is set for any special page regardless of where in GFN space it is mapped. NOTE: Clearly this mitigation only applies to Intel EPT. It is not obvious that there is any similar mitigation possible for AMD NPT. Downstreams such as Citrix XenServer have been carrying a patch similar to this for several releases though. Signed-off-by: Paul Durrant Reviewed-by: Jan Beulich --- Cc: Andrew Cooper Cc: Wei Liu Cc: "Roger Pau Monné" --- xen/arch/x86/hvm/mtrr.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/xen/arch/x86/hvm/mtrr.c b/xen/arch/x86/hvm/mtrr.c index 511c3be1c8..3ad813ed15 100644 --- a/xen/arch/x86/hvm/mtrr.c +++ b/xen/arch/x86/hvm/mtrr.c @@ -830,7 +830,8 @@ int epte_get_entry_emt(struct domain *d, unsigned long gfn, mfn_t mfn, return MTRR_TYPE_UNCACHABLE; } - if ( !is_iommu_enabled(d) && !cache_flush_permitted(d) ) + if ( (!is_iommu_enabled(d) && !cache_flush_permitted(d)) || + is_special_page(mfn_to_page(mfn)) ) { *ipat = 1; return MTRR_TYPE_WRBACK;