On Thu, Mar 19, 2015 at 06:17:46PM +0100, Denys Vlasenko wrote:
> PER_CPU_VAR(kernel_stack) was set up in a way where it points
> five stack slots below the top of stack.
>
> Presumably, it was done to avoid one "sub $5*8,%rsp"
> in syscall/sysenter code paths, where iret frame needs to be
> created by hand.
>
> Ironically, none of them benefits from this optimization,
> since all of them need to allocate additional data on stack
> (struct pt_regs), so they still have to perform subtraction.
>
> This patch eliminates KERNEL_STACK_OFFSET.
>
> PER_CPU_VAR(kernel_stack) now points directly to top of stack.
> pt_regs allocations are adjusted to allocate iret frame as well.
> Hopefully we can merge it later with 32-bit specific
> PER_CPU_VAR(cpu_current_top_of_stack) variable...
>
> Net result in generated code is that constants in several insns
> are changed.
>
> This change is necessary for changing struct pt_regs creation
> in SYSCALL64 code path from MOV to PUSH instructions.
>
> Signed-off-by: Denys Vlasenko <dvlas...@redhat.com>
> CC: Linus Torvalds <torva...@linux-foundation.org>
> CC: Steven Rostedt <rost...@goodmis.org>
> CC: Ingo Molnar <mi...@kernel.org>
> CC: Borislav Petkov <b...@alien8.de>
> CC: "H. Peter Anvin" <h...@zytor.com>
> CC: Andy Lutomirski <l...@amacapital.net>
> CC: Oleg Nesterov <o...@redhat.com>
> CC: Frederic Weisbecker <fweis...@gmail.com>
> CC: Alexei Starovoitov <a...@plumgrid.com>
> CC: Will Drewry <w...@chromium.org>
> CC: Kees Cook <keesc...@chromium.org>
> CC: x...@kernel.org
> CC: linux-kernel@vger.kernel.org
Acked-by: Borislav Petkov <b...@suse.de>
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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