x86: fix gart_iommu_init()

When the GART table is unmapped from the kernel direct mappings
during early bootup, make sure we have no leftover cachelines in it.

Note: the clflush done by set_memory_np() was not enough, because
clflush does not work on unmapped pages.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 9 insertions, 0 deletions

diff --git a/arch/x86/kernel/pci-gart_64.c b/arch/x86/kernel/pci-gart_64.c
index 65f6acb025c8..faf3229f8fb3 100644
--- a/arch/x86/kernel/pci-gart_64.c
+++ b/arch/x86/kernel/pci-gart_64.c
@@ -749,6 +749,15 @@ void __init gart_iommu_init(void)
          */
         set_memory_np((unsigned long)__va(iommu_bus_base),
                                 iommu_size >> PAGE_SHIFT);
+        /*
+         * Tricky. The GART table remaps the physical memory range,
+         * so the CPU wont notice potential aliases and if the memory
+         * is remapped to UC later on, we might surprise the PCI devices
+         * with a stray writeout of a cacheline. So play it sure and
+         * do an explicit, full-scale wbinvd() _after_ having marked all
+         * the pages as Not-Present:
+         */
+        wbinvd();
 
         /*
          * Try to workaround a bug (thanks to BenH)