From mboxrd@z Thu Jan 1 00:00:00 1970 From: Borislav Petkov Subject: Re: [PATCH 6/6] x86: Use clwb in drm_clflush_virt_range Date: Thu, 13 Nov 2014 18:11:33 +0100 Message-ID: <20141113171133.GD14070@pd.tnic> References: <1415731396-19364-1-git-send-email-ross.zwisler@linux.intel.com> <1415731396-19364-7-git-send-email-ross.zwisler@linux.intel.com> <5464220D.6090204@amacapital.net> <20141113112017.GA14416@pd.tnic> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: Received: from mail.skyhub.de (mail.skyhub.de [78.46.96.112]) by gabe.freedesktop.org (Postfix) with ESMTP id 461526E9F0 for ; Thu, 13 Nov 2014 09:11:43 -0800 (PST) Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" To: Andy Lutomirski Cc: intel-gfx@lists.freedesktop.org, X86 ML , "linux-kernel@vger.kernel.org" , DRI , Ingo Molnar , Ross Zwisler , H Peter Anvin , Thomas Gleixner List-Id: dri-devel@lists.freedesktop.org T24gVGh1LCBOb3YgMTMsIDIwMTQgYXQgMDg6Mzg6MjNBTSAtMDgwMCwgQW5keSBMdXRvbWlyc2tp IHdyb3RlOgo+IE9uIE5vdiAxMywgMjAxNCAzOjIwIEFNLCAiQm9yaXNsYXYgUGV0a292IiA8YnBA YWxpZW44LmRlPiB3cm90ZToKPiA+Cj4gPiBPbiBXZWQsIE5vdiAxMiwgMjAxNCBhdCAwNzoxNDoy MVBNIC0wODAwLCBBbmR5IEx1dG9taXJza2kgd3JvdGU6Cj4gPiA+IE9uIDExLzExLzIwMTQgMTA6 NDMgQU0sIFJvc3MgWndpc2xlciB3cm90ZToKPiA+ID4gPiBJZiBjbHdiIGlzIGF2YWlsYWJsZSBv biB0aGUgc3lzdGVtLCB1c2UgaXQgaW4gZHJtX2NsZmx1c2hfdmlydF9yYW5nZS4KPiA+ID4gPiBJ ZiBjbHdiIGlzIG5vdCBhdmFpbGFibGUsIGZhbGwgYmFjayB0byBjbGZsdXNob3B0IGlmIHlvdSBj YW4uCj4gPiA+ID4gSWYgY2xmbHVzaG9wdCBpcyBub3Qgc3VwcG9ydGVkLCBmYWxsIGFsbCB0aGUg d2F5IGJhY2sgdG8gY2xmbHVzaC4KPiA+ID4KPiA+ID4gSSBkb24ndCBrbm93IGV4YWN0bHkgd2hh dCBkcm1fY2xmbHVzaF92aXJ0X3JhbmdlIChhbmQgdGhlIG90aGVyCj4gPiA+IGZ1bmN0aW9ucyB5 b3UncmUgbW9kaWZ5aW5nIHNpbWlsYXJseSkgYXJlIGZvciwgYnV0IGl0IHNlZW1zIHBsYXVzaWJs ZSB0bwo+ID4gPiBtZSB0aGF0IHRoZXkncmUgdXNlZCBiZWZvcmUgcmVhZHMgdG8gbWFrZSBzdXJl IHRoYXQgbm9uLWNvaGVyZW50IG1lbW9yeQo+ID4gPiBzZWVzIHVwZGF0ZWQgZGF0YS4gIElmIHRo YXQncyB0cnVlLCB0aGVuIHRoaXMgd2lsbCBicmVhayBpdC4KPiA+Cj4gPiBXaHkgd291bGQgaXQg YnJlYWsgaXQ/IFRoZSB1cGRhdGVkIGNhY2hlbGluZXMgd2lsbCBiZSBpbiBtZW1vcnkgYW5kCj4g PiBzdWJzZXF1ZW50IHJlYWRzIHdpbGwgYmUgc2VydmljZWQgZnJvbSB0aGUgY2FjaGUgaW5zdGVh ZCBmcm9tIGdvaW5nIHRvCj4gPiBtZW1vcnkgYXMgaXQgaXMgbm90IGludmFsaWRhdGVkIGFzIGl0 IHdvdWxkIGJlIGJ5IENMRkxVU0guCj4gPgo+ID4gL21lIGlzIHB1enpsZWQuCj4gCj4gU3VwcG9z ZSB5b3UgbWFwIHNvbWUgZGV2aWNlIG1lbW9yeSBXQiwgYW5kIHRoZW4gdGhlIGRldmljZQo+IG5v bi1jb2hlcmVudGx5IHVwZGF0ZXMuICBJZiB5b3Ugd2FudCB0aGUgQ1BVIHRvIHNlZSBpdCwgeW91 IG5lZWQKPiBjbGZsdXNoIG9yIGNsZmx1c2hvcHQuICBTb21lIGFyY2hpdGVjdHVyZXMgbWlnaHQg ZG8gdGhpcyBmb3IKPiBkbWFfc3luY19zaW5nbGVfZm9yX2NwdSB3aXRoIERNQV9GUk9NX0RFVklD RS4KCkFoLCB5b3UncmUgdGFsa2luZyBhYm91dCB0aGUgb3RoZXIgd2F5IGFyb3VuZCAtIHRoZSBk ZXZpY2UgZG9lcyB0aGUKd3JpdGVzLiBXZWxsLCB0aGUgdXNhZ2Ugc2l0ZXMgYXJlIGFsbCBpbiBp OTE1KiwgbWF5YmUgd2Ugc2hvdWxkIGFzawp0aGVtIC0gaXQgbG9va3MgdG8gbWUgbGlrZSB0aGlz IGlzIG9ubHkgdGhlIENQVSBtYWtpbmcgc3R1ZmYgdmlzaWJsZSBpbgp0aGUgc2hhcmVkIGJ1ZmZl ciBidXQgSSBkb24ndCBrbm93IHRoYXQgY29kZS4uLiBpbnRlbC1nZnggQ0NlZCBhbHRob3VnaApk cmktZGV2ZWwgaXMgYWxyZWFkeSBvbiBDQy4KCi0tIApSZWdhcmRzL0dydXNzLAogICAgQm9yaXMu CgpTZW50IGZyb20gYSBmYXQgY3JhdGUgdW5kZXIgbXkgZGVzay4gRm9ybWF0dGluZyBpcyBmaW5l LgotLQpfX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fXwpkcmkt ZGV2ZWwgbWFpbGluZyBsaXN0CmRyaS1kZXZlbEBsaXN0cy5mcmVlZGVza3RvcC5vcmcKaHR0cDov L2xpc3RzLmZyZWVkZXNrdG9wLm9yZy9tYWlsbWFuL2xpc3RpbmZvL2RyaS1kZXZlbAo= From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933480AbaKMRLo (ORCPT ); Thu, 13 Nov 2014 12:11:44 -0500 Received: from mail.skyhub.de ([78.46.96.112]:56684 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933132AbaKMRLl (ORCPT ); Thu, 13 Nov 2014 12:11:41 -0500 Date: Thu, 13 Nov 2014 18:11:33 +0100 From: Borislav Petkov To: Andy Lutomirski Cc: DRI , Ross Zwisler , X86 ML , Thomas Gleixner , David Airlie , H Peter Anvin , Ingo Molnar , "linux-kernel@vger.kernel.org" , intel-gfx@lists.freedesktop.org Subject: Re: [PATCH 6/6] x86: Use clwb in drm_clflush_virt_range Message-ID: <20141113171133.GD14070@pd.tnic> References: <1415731396-19364-1-git-send-email-ross.zwisler@linux.intel.com> <1415731396-19364-7-git-send-email-ross.zwisler@linux.intel.com> <5464220D.6090204@amacapital.net> <20141113112017.GA14416@pd.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 13, 2014 at 08:38:23AM -0800, Andy Lutomirski wrote: > On Nov 13, 2014 3:20 AM, "Borislav Petkov" wrote: > > > > On Wed, Nov 12, 2014 at 07:14:21PM -0800, Andy Lutomirski wrote: > > > On 11/11/2014 10:43 AM, Ross Zwisler wrote: > > > > If clwb is available on the system, use it in drm_clflush_virt_range. > > > > If clwb is not available, fall back to clflushopt if you can. > > > > If clflushopt is not supported, fall all the way back to clflush. > > > > > > I don't know exactly what drm_clflush_virt_range (and the other > > > functions you're modifying similarly) are for, but it seems plausible to > > > me that they're used before reads to make sure that non-coherent memory > > > sees updated data. If that's true, then this will break it. > > > > Why would it break it? The updated cachelines will be in memory and > > subsequent reads will be serviced from the cache instead from going to > > memory as it is not invalidated as it would be by CLFLUSH. > > > > /me is puzzled. > > Suppose you map some device memory WB, and then the device > non-coherently updates. If you want the CPU to see it, you need > clflush or clflushopt. Some architectures might do this for > dma_sync_single_for_cpu with DMA_FROM_DEVICE. Ah, you're talking about the other way around - the device does the writes. Well, the usage sites are all in i915*, maybe we should ask them - it looks to me like this is only the CPU making stuff visible in the shared buffer but I don't know that code... intel-gfx CCed although dri-devel is already on CC. -- Regards/Gruss, Boris. Sent from a fat crate under my desk. Formatting is fine. --