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authorSuresh Siddha <suresh.b.siddha@intel.com>2009-10-26 13:21:32 -0800
committerJesse Barnes <jbarnes@virtuousgeek.org>2009-11-04 08:47:22 -0800
commit2992e545ea006992ec9dc91c4fa996ce1e15f921 (patch)
tree5e3760376716e96d97e7533c01ffb52c4fb66d31 /arch/x86/pci/i386.c
parent9a007b3791cdba3601d835ea10e68c14115b9afb (diff)
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 <thomas.schlichter@web.de> Signed-off-by: Thomas Schlichter <thomas.schlichter@web.de> Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com> Acked-by: Eric Anholt <eric@anholt.net> Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org> Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Diffstat (limited to 'arch/x86/pci/i386.c')
-rw-r--r--arch/x86/pci/i386.c9
1 files changed, 9 insertions, 0 deletions
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)