On Sat, Apr 27, 2019 at 10:47 PM Mike Rapoport <rppt@xxxxxxxxxxxxx> wrote: > > On Fri, Apr 26, 2019 at 09:42:23AM +0200, Peter Zijlstra wrote: > > On Fri, Apr 26, 2019 at 12:45:52AM +0300, Mike Rapoport wrote: > > > If a system call runs in isolated context, it's accesses to kernel code and > > > data will be verified by SCI susbsytem. > > > > > > Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx> > > > --- > > > arch/x86/mm/fault.c | 28 ++++++++++++++++++++++++++++ > > > 1 file changed, 28 insertions(+) > > > > There's a distinct lack of touching do_double_fault(). It appears to me > > that you'll instantly trigger #DF when you #PF, because the #PF handler > > itself will not be able to run. > > The #PF handler is able to run. On interrupt/error entry the cr3 is > switched to the full kernel page tables, pretty much like PTI does for > user <-> kernel transitions. It's in the patch 3. > > PeterZ meant page_fault, not do_page_fault. In your patch, page_fault and some of error_entry run before that magic switchover happens. If they're not in the page tables, you double-fault. And don't even try to do SCI magic in the double-fault handler. As I understand it, the SDM and APM aren't kidding when they say that #DF is an abort, not a fault. There is a single case in the kernel where we recover from #DF, and it was vetted by microcode people.
