On 11/10/2017 02:06 PM, Andy Lutomirski wrote: > On Thu, Nov 9, 2017 at 10:31 PM, Dave Hansen > <dave.hansen@xxxxxxxxxxxxxxx> wrote: >> On 11/09/2017 06:25 PM, Andy Lutomirski wrote: >>> Here are two proposals to address this without breaking vsyscalls. >>> >>> 1. Set NX on low mappings that are _PAGE_USER. Don't set NX on high >>> mappings but, optionally, warn if you see _PAGE_USER on any address >>> that isn't the vsyscall page. >>> >>> 2. Ignore _PAGE_USER entirely and just mark the EFI mm as special so >>> KAISER doesn't muck with it. >> >> These are totally doable. But, what's the big deal with breaking native >> vsyscall? We can still do the emulation so nothing breaks: it is just slow. > > I have nothing against disabling native. I object to breaking the > weird binary tracing behavior in the emulation mode, especially if > it's tangled up with KAISER. I got all kinds of flak in an earlier > version of the vsyscall emulation patches when I broke that use case. > KAISER may get very widely backported -- let's not make changes that > are already known to break things. Is the thing that broke a "user mode program that actually looks at the vsyscall page"? Like Linus is referring to here: > http://lkml.kernel.org/r/CA+55aFyijHb4WnDMKgeXekTZHYT8pajqSAu2peo3O4EKiZbYPA@xxxxxxxxxxxxxx -- 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>
