Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753070AbbFKOpC (ORCPT ); Thu, 11 Jun 2015 10:45:02 -0400 Received: from casper.infradead.org ([85.118.1.10]:40588 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752697AbbFKOo7 (ORCPT ); Thu, 11 Jun 2015 10:44:59 -0400 Message-ID: <1434033896.3907.61.camel@infradead.org> Subject: Re: [PATCH 2/4] iommu/vt-d: Don't consider copied context entries as present From: David Woodhouse To: Joerg Roedel Cc: Joerg Roedel , iommu@lists.linux-foundation.org, zhen-hual@hp.com, bhe@redhat.com, linux-kernel@vger.kernel.org Date: Thu, 11 Jun 2015 15:44:56 +0100 In-Reply-To: <20150611142554.GG16345@suse.de> References: <1434030463-942-1-git-send-email-joro@8bytes.org> <1434030463-942-3-git-send-email-joro@8bytes.org> <1434031622.3907.40.camel@infradead.org> <20150611142554.GG16345@suse.de> Content-Type: multipart/signed; micalg="sha-1"; protocol="application/x-pkcs7-signature"; boundary="=-WqEiEi+jbsH7tnWlp6o/" X-Mailer: Evolution 3.16.2.1 (3.16.2.1-2.fc22) Mime-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 11550 Lines: 197 --=-WqEiEi+jbsH7tnWlp6o/ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2015-06-11 at 16:25 +0200, Joerg Roedel wrote: > On Thu, Jun 11, 2015 at 03:07:02PM +0100, David Woodhouse wrote: > > On Thu, 2015-06-11 at 15:47 +0200, Joerg Roedel wrote: > > > From: Joerg Roedel > > >=20 > > > Hide the copied context entries from the IOMMU driver by > > > considering them as non-present. This is implemented by > > > setting the first AVL bit (bit 67) in the context entry to > > > one. If this bit is set, the context_present() function > > > returns false. > > >=20 > > > Signed-off-by: Joerg Roedel > >=20 > > In the extended context entry, bit 67 is the PGE bit. There are no bits > > which are available to software, to my knowledge. >=20 > Okay, reading the VT-d spec again, the extended context-entry table seem > to exist in parallel to the current context-entry table, right? So this > patch should still work, even with extended entries present. No, the extended context-entry exists *instead* of the legacy context-entry. Note that all the bits in the legacy context-entry are present in precisely the same place in the extended context-entry. It's just that the extended context-entry defines meanings for more of them. When you enable the DMA_RTADDR_RTT bit in the Root Table Address register, the context-entries magically double in size. It used to look like this: Root Table Address Register | V Root Table (struct root_entry) Context Table (struct context_entry) ------------------------------ ------------------------------------ 0x00: Context-table pointer -----> Context entry for 00:00.0 0x08: unused Context entry for 00:00.1=20 0x10: unused Context entry for 00:00.2 ... ... ... 0xff8:... Context entry for ff:1f.7 Now it looks like this Root Table Address Register | V Root Table (struct root_entry) Context Table (struct context_entry) ------------------------------ ------------------------------------ 0x00: Context-table ptr #1 -----> Context entry for 00:00.0: lo 0x08: Context-table ptr #2 --, Context entry for 00:00.0: hi 0x10: unused | Context entry for 00:00.1: lo ... ... | ... 0xff8:... | Context entry for 7f:1f.7: hi | | | Context Table (struct context_entry) --> ------------------------------------ 0x00: Context entry for 80:00.0: lo 0x08: Context entry for 80:00.1: hi ... ... 0xff8: Context entry for ff:1f.7: hi This was implemented in http://git.kernel.org/linus/03ecc32c52 but *all* that patch did was allocate the second page of context-table, fill in the appropriate new pointer in the root table, and adjust the way we calculate the *location* of a context-entry. In 4.1 we're still only using the same old bits of the context-entry, which as noted are in the same place in both cases. Even the mapping from the old 2-bit T field to the new 3-bit TT field works out that way, for now. --=20 dwmw2 --=-WqEiEi+jbsH7tnWlp6o/ Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIISjjCCBicw ggUPoAMCAQICAw3vNzANBgkqhkiG9w0BAQUFADCBjDELMAkGA1UEBhMCSUwxFjAUBgNVBAoTDVN0 YXJ0Q29tIEx0ZC4xKzApBgNVBAsTIlNlY3VyZSBEaWdpdGFsIENlcnRpZmljYXRlIFNpZ25pbmcx ODA2BgNVBAMTL1N0YXJ0Q29tIENsYXNzIDEgUHJpbWFyeSBJbnRlcm1lZGlhdGUgQ2xpZW50IENB MB4XDTE1MDUwNTA5NDM0MVoXDTE2MDUwNTA5NTMzNlowQjEcMBoGA1UEAwwTZHdtdzJAaW5mcmFk ZWFkLm9yZzEiMCAGCSqGSIb3DQEJARYTZHdtdzJAaW5mcmFkZWFkLm9yZzCCASIwDQYJKoZIhvcN AQEBBQADggEPADCCAQoCggEBAMkbm9kPbx1j/X4RVyf/pPKSYwelcco69TvnQQbKM8m8xkWjXJI1 jpJ1jMaGUZGFToINMSZi7lZawUozudWbXSKy1SikENSTJHffsdRAIlsp+hR8vWvjsKUry6sEdqPG doa5RY7+N4WRusWZDYW/RRWE6i9EL9qV86CVPYqw22UBOUw4/j/HVGCV6TSB8yE5iEwhk/hUuzRr 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