At the moment the protection in VFIO MMIO mappings is forced to _PAGE_NON_IDEMPOTENT which means that write combining is not really available to the userspace even for prefetchable 64bit MMIO BARs. This replaces pgprot_noncached() with a platform specific phys_mem_access_prot() when available and depending on the platform the vm_page_prot may be set to _PAGE_TOLERANT allowing to exploit the write combining feature. The guest drivers still have to use _wc versions of the ioremap/pci_ioremap API to get write combininig working. Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx> --- This should allow DPDK and radix guests (x86, POWERPC, etc) to do write combining. POWERPC hash guests should not be affected by this change, it should work even without this. --- drivers/vfio/pci/vfio_pci.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c index f041b1a6cf66..014192b42724 100644 --- a/drivers/vfio/pci/vfio_pci.c +++ b/drivers/vfio/pci/vfio_pci.c @@ -1156,8 +1156,13 @@ static int vfio_pci_mmap(void *device_data, struct vm_area_struct *vma) } vma->vm_private_data = vdev; - vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); vma->vm_pgoff = (pci_resource_start(pdev, index) >> PAGE_SHIFT) + pgoff; +#ifdef __HAVE_PHYS_MEM_ACCESS_PROT + vma->vm_page_prot = phys_mem_access_prot(NULL, vma->vm_pgoff, + req_len, vma->vm_page_prot); +#else + vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); +#endif return remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff, req_len, vma->vm_page_prot); -- 2.11.0
