On 2024/2/28 10:10, Matthew Wilcox wrote: > On Wed, Feb 28, 2024 at 09:55:24AM +0800, mawupeng wrote: >> On 2024/2/27 21:15, David Hildenbrand wrote: >>> On 27.02.24 14:00, David Hildenbrand wrote: >>>> On 27.02.24 13:28, Wupeng Ma wrote: >>>>> We find that a warn will be produced during our test, the detail log is >>>>> shown in the end. >>>>> >>>>> The core problem of this warn is that the first pfn of this pfnmap vma is >>>>> cleared during memory-failure. Digging into the source we find that this >>>>> problem can be triggered as following: >>>>> >>>>> // mmap with MAP_PRIVATE and specific fd which hook mmap >>>>> mmap(MAP_PRIVATE, fd) >>>>> __mmap_region >>>>> remap_pfn_range >>>>> // set vma with pfnmap and the prot of pte is read only >>>>> >>>> >>>> Okay, so we get a MAP_PRIVATE VM_PFNMAP I assume. >>>> >>>> What fd is that exactly? Often, we disallow private mappings in the >>>> mmap() callback (for a good reason). >> >> just a device fd with device-specify mmap which use remap_pfn_range to assign memory. > > But what meaning do you want MAP_PRIVATE of this fd to have? Does it > make sense to permit this, or should you rather just return -EINVAL if > somebody tries to mmap() with MAP_PRIVATE set? I think return -EINVAL if somebody tries to mmap() with MAP_PRIVATE and MAP_MAYWRITE is reasonable to me. Read to this pfnmap vma will not trigger fault. >
