From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.136]:40176 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751852AbdDQVgu (ORCPT ); Mon, 17 Apr 2017 17:36:50 -0400 Subject: [PATCH v11 3/7] PCI: Add pcibios_default_alignment() for arch-specific alignment control From: Bjorn Helgaas To: Yongji Xie Cc: zhong@linux.vnet.ibm.com, Alexey Kardashevskiy , linux-pci@vger.kernel.org, Gavin Shan , Alex Williamson , Paul Mackerras , Michael Ellerman , Benjamin Herrenschmidt , linuxppc-dev@lists.ozlabs.org Date: Mon, 17 Apr 2017 16:36:46 -0500 Message-ID: <20170417213646.21092.24262.stgit@bhelgaas-glaptop.roam.corp.google.com> In-Reply-To: <20170417212705.21092.90222.stgit@bhelgaas-glaptop.roam.corp.google.com> References: <20170417212705.21092.90222.stgit@bhelgaas-glaptop.roam.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Sender: linux-pci-owner@vger.kernel.org List-ID: From: Yongji Xie When VFIO passes through a PCI device to a guest, it does not allow the guest to mmap BARs that are smaller than PAGE_SIZE unless it can reserve the rest of the page (see vfio_pci_probe_mmaps()). This is because a page might contain several small BARs for unrelated devices and a guest should not be able to access all of them. VFIO emulates guest accesses to non-mappable BARs, which is functional but slow. On systems with large page sizes, e.g., PowerNV with 64K pages, BARs are more likely to share a page and performance is more likely to be a problem. Add a weak function to set default alignment for all PCI devices. An arch can override it to force the PCI core to place memory BARs on their own pages. Signed-off-by: Yongji Xie Signed-off-by: Bjorn Helgaas --- drivers/pci/pci.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index 679af2a253ad..a2d1f144c94f 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -4947,6 +4947,11 @@ void pci_ignore_hotplug(struct pci_dev *dev) } EXPORT_SYMBOL_GPL(pci_ignore_hotplug); +resource_size_t __weak pcibios_default_alignment(struct pci_dev *dev) +{ + return 0; +} + #define RESOURCE_ALIGNMENT_PARAM_SIZE COMMAND_LINE_SIZE static char resource_alignment_param[RESOURCE_ALIGNMENT_PARAM_SIZE] = {0}; static DEFINE_SPINLOCK(resource_alignment_lock); @@ -4962,14 +4967,15 @@ static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev) { int seg, bus, slot, func, align_order, count; unsigned short vendor, device, subsystem_vendor, subsystem_device; - resource_size_t align = 0; + resource_size_t align = pcibios_default_alignment(dev); char *p; spin_lock(&resource_alignment_lock); p = resource_alignment_param; - if (!*p) + if (!*p && !align) goto out; if (pci_has_flag(PCI_PROBE_ONLY)) { + align = 0; pr_info_once("PCI: Ignoring requested alignments (PCI_PROBE_ONLY)\n"); goto out; }