On Mon, Oct 16, 2017 at 4:55 AM, Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote: > On Sat, Oct 14, 2017 at 01:19:08PM -0400, Brian Gerst wrote: >> From what we've seen with the TLB flush rework, having potential >> garbage in the page tables that speculative reads can see can cause >> bad things like machine checks. It would be best to have a second >> temporary page just for the page table (and properly cleared). > > Hm. Interesting. Is there a place where I can read more about this? I believe this thread was where it was first reported: https://lkml.org/lkml/2017/9/5/152 >> The trampoline also needs its own stack, in case the stack pointer was >> above 4G. > > You are right, we need new stack. I've missed that. > >> That could be at the end of the code page, since you only need 8 bytes. > > When I wrote about 8 bytes, I referred the usage of page table, not code. > We use more than 8 bytes of code, but this should enough in the page. What I meant was, on one page, have the code at the start of the page, and the stack at the end. You only need 8 bytes of stack to push the far pointer to return to 64-bit mode. The page table would be on the second page. -- Brian Gerst -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
