On Tue, Feb 28, 2023 at 5:40 AM <kirill@xxxxxxxxxxxxx> wrote: > > On Wed, Feb 08, 2023 at 03:00:59PM -0800, Jiaqi Yan wrote: > > On Wed, Feb 8, 2023 at 3:45 AM Alexander Potapenko <glider@xxxxxxxxxx> wrote: > > > > > > On Tue, Feb 7, 2023 at 7:20 PM Jiaqi Yan <jiaqiyan@xxxxxxxxxx> wrote: > > > > > > > > Pinging KMSAN experts, for the general guidance of > > > > kmsan_copy_page_meta vs kmsan_unpoison_memory > > > > > > Oh, sorry, I've missed the previous email. > > > > NP, thanks for jumping in :) > > > > > > > > copy_mc_user_highpage() is expected to copy data from the user page, > > > for which no metadata is ever allocated. > > > Therefore we just initialize the destination shadow with zeros instead > > > of copying anything. > > > > > > kmsan_copy_page_meta() is used when the metadata is copied between two > > > kernel pages, therefore it handles the cases when page->kmsan_shadow > > > is NULL for the source and destination pages. > > > > > > It might be a good idea to use kmsan_copy_page_meta() in both cases, > > > but to do that I want to better understand what happens when > > > kmap_local_page(from) is called in copy_mc_user_highpage(). > > > Where does the corresponding struct page come from? > > > > Kirill can correct me, but I think khugepaged always copies user pages > > because it is trying to convert raw pages to THP for better userspace > > application performance. Therefore khugepaged should only need > > copy_mc_user_highpage(), for both file-backed and anonymous memory > > pages. > > > > However, copy_mc_user_highpage() needs both vaddr and vma, so it is a > > little bit hard to use it in collapse_file (i.e. in the file-backed > > case): > > 1. vma is not carried over to collapse_file from khugepaged_scan_mm_slot > > 2. collapse_file is not directly iterating with vaddrs of pages to be copied > > > > (Although both vaddr and vma are unused auguments in > > copy_mc_user_highpage, I think for cleanness, the caller e.g. > > khugepaged should feed valid values). > > It is not unused for !copy_mc_to_kernel case (basically everything but x86 > and power). And it is used to flush caches. The fact that you don't have > it in your implementation *may* indicate a problem. ah, I agree this looks problematic. Maybe I should give up on unifying the copying routine used by anon and file memory: * for anon, switch to copy_mc_user_highpage, which "works" for all architectures, but #MC is only recoverable on x86 and powerpc. * for shmem, extend copy_highpage to copy_mc_highpage, like how Tony makes copy_mc_user_highpage. > > > So my patchset uses copy_mc_page(and kmsan_copy_page_meta) for both > > file-backed and anon memory pages. I guess as long as > > kmsan_copy_page_meta doesn't do anything unexpected for user pages (at > > least from my reading), we are good? > > > > -- > Kiryl Shutsemau / Kirill A. Shutemov
