Messages in this thread | | | From | Linus Torvalds <> | Date | Wed, 17 Jan 2018 11:26:08 -0800 | Subject | Re: [PATCH v3 8/9] x86: use __uaccess_begin_nospec and ASM_IFENCE in get_user paths |
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On Wed, Jan 17, 2018 at 6:17 AM, Alan Cox <alan@linux.intel.com> wrote: > > Can we kill off the remaining users of set_fs() ?
I would love to, but it's not going to happen short-term. If ever.
Some could be removed today: the code in arch/x86/net/bpf_jit_comp.c seems to be literally the ramblings of a diseased mind. There's no reason for the set_fs(), there's no reason for the flush_icache_range() (it's a no-op on x86 anyway), and the smp_wmb() looks bogus too.
I have no idea how that braindamage happened, but I assume it got copied from some broken source.
But there are about ~100 set_fs() calls in generic code, and some of those really are pretty fundamental. Doing things like "kernel_read()" without set_fs() is basically impossible.
We've had set_fs() since the beginning. The naming is obviously very historical. We have it for a very good reason, and I don't really see that reason going away.
So realistically, we want to _minimize_ set_fs(), and we might want to make sure that it's done only in limited settings (it might, for example, be a good idea and a realistic goal to make sure that drivers and modules can't do it, and use proper helper functions like that "read_kernel()").
But getting rid of the concept entirely? Doesn't seem likely.
Linus
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