From 2992e545ea006992ec9dc91c4fa996ce1e15f921 Mon Sep 17 00:00:00 2001 From: Suresh Siddha Date: Mon, 26 Oct 2009 13:21:32 -0800 Subject: [PATCH] x86/PCI/PAT: return EINVAL for pci mmap WC request for !pat_enabled Thomas Schlichter reported: > X.org uses libpciaccess which tries to mmap with write combining enabled via > /sys/bus/pci/devices/*/resource0_wc. Currently, when PAT is not enabled, the > kernel does fall back to uncached mmap. Then libpciaccess thinks it succeeded > mapping with write combining enabled and does not set up suited MTRR entries. > ;-( Instead of silently mapping pci mmap region as UC minus in the case of !pat_enabled and wc request, we can return error. Eric Anholt mentioned that caller (like X) typically follows up with UC minus pci mmap request and if there is a free mtrr slot, caller will manage adding WC mtrr. Jesse Barnes says: > Older versions of libpciaccess will behave better if we do it that way > (iirc it only allocates an MTRR if the resource_wc file doesn't exist or > fails to get mapped). Reported-by: Thomas Schlichter Signed-off-by: Thomas Schlichter Signed-off-by: Suresh Siddha Acked-by: Eric Anholt Acked-by: Jesse Barnes Signed-off-by: Jesse Barnes --- arch/x86/pci/i386.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/x86/pci/i386.c b/arch/x86/pci/i386.c index a70a85de5e8..52e656f1778 100644 --- a/arch/x86/pci/i386.c +++ b/arch/x86/pci/i386.c @@ -280,6 +280,15 @@ int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma, return -EINVAL; prot = pgprot_val(vma->vm_page_prot); + + /* + * Return error if pat is not enabled and write_combine is requested. + * Caller can followup with UC MINUS request and add a WC mtrr if there + * is a free mtrr slot. + */ + if (!pat_enabled && write_combine) + return -EINVAL; + if (pat_enabled && write_combine) prot |= _PAGE_CACHE_WC; else if (pat_enabled || boot_cpu_data.x86 > 3)