On Wed, 2022-10-12 at 14:18 +0200, Florian Weimer wrote: > * Rick P. Edgecombe: > > > On Mon, 2022-10-10 at 12:56 +0200, Florian Weimer wrote: > > > > + /* Only support enabling/disabling one feature at a time. > > > > */ > > > > + if (hweight_long(features) > 1) > > > > + return -EINVAL; > > > > > > This means we'll soon need three extra system calls for x86-64 > > > process > > > start: SHSTK, IBT, and switching off vsyscall emulation. (The > > > latter > > > does not need any special CPU support.) > > > > > > Maybe we can do something else instead to make the strace output > > > a > > > little bit cleaner? > > > > In previous versions it supported enabling multiple features in a > > single syscall. Thomas Gleixner pointed out that (this was on the > > LAM > > patchset that shared the interface at the time) it makes the > > behavior > > of what to do when one feature fails to enable complicated: > > > > https://lore.kernel.org/lkml/87zgjjqico.ffs@tglx/ > > Can we return the bits for the features that were actually enabled? Actually that specific option is covered in that thread as well. I was thinking we would need to pass a struct in an out to do a batch operation. Thomas suggested it could be added later and to start with a simpler option. Is an extra syscall or two at startup really a big problem? > Those three don't have cross-dependencies in the sense that you would > only use X & Y together, but not X or Y alone. I don't fully follow this, but WRSS does actually depend on SHSTK.
