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=-13.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FAKE_REPLY_C,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 BADC5C282DD for ; Tue, 7 Jan 2020 21:13:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8C3FD2077B for ; Tue, 7 Jan 2020 21:13:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578431627; bh=i1qhWJd/JIv/EvnYvOd+bBbFKX9FBjpyZH4/2g/2b4U=; h=Date:From:To:Cc:Subject:In-Reply-To:List-ID:From; b=SRUQ1TTb4gD72zlLVuMkVcHAZFSvDDXBkKdD8c1ck9LEk6wUyidooxKlt6xaxWPe0 aFplYq8t/4YX4MrzDsZT6z7Ch+qxKrOTOReqE3BGlb76ptDNjwOk0K9INVDOBnkvOs mYQh1APffJHUz5KNoYwEAkAG6kFB4mANo6iYOoq8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730089AbgAGVNq (ORCPT ); Tue, 7 Jan 2020 16:13:46 -0500 Received: from mail.kernel.org ([198.145.29.99]:45832 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729946AbgAGVNl (ORCPT ); Tue, 7 Jan 2020 16:13:41 -0500 Received: from localhost (mobile-166-170-223-177.mycingular.net [166.170.223.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 26725208C4; Tue, 7 Jan 2020 21:13:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578431620; bh=i1qhWJd/JIv/EvnYvOd+bBbFKX9FBjpyZH4/2g/2b4U=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=VuyNT0vx/XbudQ2Gbc0TGX2wUKpjZv8Weu0kKC6w8ql8rK+p+I6Zf+yC9SMZqgwCW Q1DVei+Qm4jH8R1L7n1tMnA3gUlctkjgB0K0EoYsaU8GWktZbT2H5WTEkzdUtHha2x qludjgYJgeEv42vJifBCoYC8egPNQv2is8kgOstI= Date: Tue, 7 Jan 2020 15:13:38 -0600 From: Bjorn Helgaas To: Logan Gunthorpe Cc: linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, Kit Chow , Benjamin Herrenschmidt , Nicholas Johnson , Mika Westerberg Subject: Re: [PATCH v4] PCI: Fix disabling of bridge BARs when assigning bus resources Message-ID: <20200107211338.GA31548@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200107190902.5093-1-logang@deltatee.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 07, 2020 at 12:09:02PM -0700, Logan Gunthorpe wrote: > One odd quirk of PLX switches is that their upstream bridge port has > 256K of space allocated behind its BAR0 (most other bridge > implementations do not report any BAR space). The lspci for such device > looks like: > > 04:00.0 PCI bridge: PLX Technology, Inc. PEX 8724 24-Lane, 6-Port PCI > Express Gen 3 (8 GT/s) Switch, 19 x 19mm FCBGA (rev ca) > (prog-if 00 [Normal decode]) > Physical Slot: 1 > Flags: bus master, fast devsel, latency 0, IRQ 30, NUMA node 0 > Memory at 90a00000 (32-bit, non-prefetchable) [size=256K] > Bus: primary=04, secondary=05, subordinate=0a, sec-latency=0 > I/O behind bridge: 00002000-00003fff > Memory behind bridge: 90000000-909fffff > Prefetchable memory behind bridge: 0000380000800000-0000380000bfffff > Kernel driver in use: pcieport > > It's not clear what the purpose of the memory at 0x90a00000 is, and > currently the kernel never actually uses it for anything. In most cases, > it's safely ignored and does not cause a problem. > > However, when the kernel assigns the resource addresses (with the > pci=realloc command line parameter, for example) it can inadvertently > disable the struct resource corresponding to the bar. When this happens, > lspci will report this memory as ignored: > > Region 0: Memory at (32-bit, non-prefetchable) [size=256K] > > This is because the kernel reports a zero start address and zero flags > in the corresponding sysfs resource file and in /proc/bus/pci/devices. > Investigation with 'lspci -x', however shows the bios-assigned address > will still be programmed in the device's BAR registers. > > It's clearly a bug that the kernel's view of the registers differs from > what's actually programmed in the BAR, but in most cases, this still > won't result in a visibile issue because nothing uses the memory, > so nothing is affected. However, a big problem shows up when an IOMMU > is in use: the IOMMU will not reserve this space in the IOVA because the > kernel no longer thinks the range is valid. (See > dmar_init_reserved_ranges() for the Intel implementation of this.) > > Without the proper reserved range, we have a situation where a DMA > mapping may occasionally allocate an IOVA which the PCI bus will actually > route to a BAR in the PLX switch. This will result in some random DMA > writes not actually writing to the RAM they are supposed to, or random > DMA reads returning all FFs from the PLX BAR when it's supposed to have > read from RAM. > > The problem is caused in pci_assign_unassigned_root_bus_resources(). > When any resource from a bridge device fails to get assigned, the code > sets the resource's flags to zero. This makes sense for bridge resources, > as they will be re-enabled later, but for regular BARs, it disables them > permanently. > > The code in question seems to indent to check if "dev->subordinate" is > zero to determine whether a device is a bridge, however this is not > likely valid as there might be a bridge without a subordinate bus due to > running out of bus numbers or other cases. > > To fix these issues we instead check that the idx is in the > PCI_BRIDGE_RESOURCES range which are only used for bridge windows and > thus is sufficient for the "dev->subordinate" check and will also > prevent the bug above from clobbering PLX devices' regular BARs. s/bios/BIOS/ s/bar/BAR/ s/visibile/visible/ s/indent/intend/ > Reported-by: Kit Chow > Fixes: da7822e5ad71 ("PCI: update bridge resources to get more big ranges when allocating space (again)") > Signed-off-by: Logan Gunthorpe > Cc: Bjorn Helgaas > --- > drivers/pci/setup-bus.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > This patch was last submitted back in June as part of a series. I've > dropped the first patch in the series as a similar patch from Nicholas > takes care of the bug. > > As a reminder, the previous discussion on this patch is here[1]. Per the > feedback, I've updated the patch to remove the check on > "dev->subordinate" entirely. > > The patch is based on v5.5-rc5 and a git branch is available here: > > https://github.com/sbates130272/linux-p2pmem pci_realloc_v4 > > [1] https://lore.kernel.org/linux-pci/20190617135307.GA13533@google.com/ > > diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c > index f279826204eb..23f6c95f3fd7 100644 > --- a/drivers/pci/setup-bus.c > +++ b/drivers/pci/setup-bus.c > @@ -1803,11 +1803,15 @@ void pci_assign_unassigned_root_bus_resources(struct pci_bus *bus) > /* Restore size and flags */ > list_for_each_entry(fail_res, &fail_head, list) { > struct resource *res = fail_res->res; > + int idx; > > res->start = fail_res->start; > res->end = fail_res->end; > res->flags = fail_res->flags; > - if (fail_res->dev->subordinate) > + > + idx = res - &fail_res->dev->resource[0]; > + if (idx >= PCI_BRIDGE_RESOURCES && > + idx <= PCI_BRIDGE_RESOURCE_END) > res->flags = 0; So I guess previously, for everything on the fail_head list, we restored flags/start/end *and* we cleared flags for every BAR and window of a bridge. Now we'll clear flags for only for bridge windows. I'm sure that was the original intent, but I don't see why we bother. The next thing we do is go back to "again", where we call __pci_bus_size_bridges(), where we immediately call pci_bridge_check_ranges(), which recomputes the flags. Is there actually any point in clearing res->flags, or could we just do this: res->start = fail_res->start; res->end = fail_res->end; res->flags = fail_res->flags; - if (fail_res->dev->subordinate) - res->flags = 0; } free_list(&fail_head);