From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-x244.google.com (mail-pg0-x244.google.com [IPv6:2607:f8b0:400e:c05::244]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3w1pgd6YVDzDqFn for ; Mon, 10 Apr 2017 22:01:33 +1000 (AEST) Received: by mail-pg0-x244.google.com with SMTP id 79so25504515pgf.0 for ; Mon, 10 Apr 2017 05:01:33 -0700 (PDT) From: Yongji Xie To: bhelgaas@google.com Cc: linux-pci@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, alex.williamson@redhat.com, gwshan@linux.vnet.ibm.com, aik@ozlabs.ru, benh@kernel.crashing.org, mpe@ellerman.id.au, paulus@samba.org, zhong@linux.vnet.ibm.com Subject: [PATCH v10 2/4] PCI: Add pcibios_default_alignment() for arch-specific alignment control Date: Mon, 10 Apr 2017 19:58:12 +0800 Message-Id: <1491825494-19331-3-git-send-email-elohimes@gmail.com> In-Reply-To: <1491825494-19331-1-git-send-email-elohimes@gmail.com> References: <1491825494-19331-1-git-send-email-elohimes@gmail.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 --- 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 7904d02..02f1255 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; } -- 1.7.9.5